agronomy
Article
Optimisation of Charcoal and Sago (Metroxylon sagu) Bark Ash
to Improve Phosphorus Availability in Acidic Soils
Prisca Divra Johan 1, Osumanu Haruna Ahmed 1,2,3,*, Ali Maru 4, Latifah Omar 1,2 and Nur Aainaa Hasbullah 5
1 Department of Crop Science, Faculty of Agricultural Science and Forestry, Bintulu Sarawak Campus,
Universiti Putra Malaysia, Bintulu 97008, Malaysia; prisca.divra@gmail.com (P.D.J.);
latifahomar@upm.edu.my (L.O.)
2 Institute Ekosains Borneo (IEB), Faculty of Agriculture and Forestry Sciences, Bintulu Sarawak Campus,
Universiti Putra Malaysia, Bintulu 97008, Malaysia
3 Institute of Tropical Agriculture, Universiti Putra Malaysia (ITAFoS), Seri Kembangan 43000, Malaysia
4 School of Agriculture, SIREC, CBAS, University of Ghana, Legon, Accra 23321, Ghana; alimaru53@gmail.com
5 Faculty of Sustainable Agriculture, Sandakan Campus, Universiti Malaysia Sabah, Sandakan 90509, Malaysia;
aainaa.hasbullah@ums.edu.my
* Correspondence: osumanu@upm.edu.my; Tel.: +60-19-3695095
Abstract: Soil acidity is an important soil factor affecting crop growth and development. This
ultimately limits crop productivity and the profitability of farmers. Soil acidity increases the toxicity
of Al, Fe, H, and Mn. The abundance of Al and Fe ions in weathered soils has been implicated in P
fixation. To date, limited research has attempted to unravel the use of charcoal with the incorporation
of sago (Metroxylon sagu) bark ash to reduce P fixation. Therefore, an incubation study was conducted
in the Soil Science Laboratory of Universiti Putra Malaysia Bintulu Sarawak Campus, Malaysia for
90 days to determine the optimum amounts of charcoal and sago bark ash that could be used to



 improve the P availability of a mineral acidic soil. Charcoal and sago bark ash rates varied by


25%, whereas Egypt rock phosphate (ERP) rate was fixed at 100% of the recommendation rate.
Citation: Johan, P.D.; Ahmed, O.H.; Soil available P was determined using the Mehlich 1 method, soil total P was extracted using the
Maru, A.; Omar, L.; Hasbullah, N.A. aqua regia method, and inorganic P was fractionated using the sequential extraction method based
Optimisation of Charcoal and Sago on its relative solubility. Other selected soil chemical properties were determined using standard
(Metroxylon sagu) Bark Ash to
procedures. The results reveal that co-application of charcoal, regardless of rate, substantially
Improve Phosphorus Availability in
increased soil total carbon. In addition, application of 75% sago bark ash increased soil pH and at the
Acidic Soils. Agronomy 2021, 11, 1803.
https://doi.org/10.3390/ same time, it reduced exchangeable acidity, Al
3+, and Fe2+. Additionally, amending acidic soils with
agronomy11091803 both charcoal and sago bark ash positively enhanced the availability of K, Ca, Mg, and Na. Although
there was no significant improvement in soil Mehlich-P with or without charcoal and sago bark
Received: 29 April 2021 ash, the application of these amendments altered inorganic P fractions in the soil. Calcium-bound
Accepted: 3 June 2021 phosphorus was more pronounced compared with Al-P and Fe-P for the soil with ERP, charcoal, and
Published: 8 September 2021 sago bark ash. The findings of this study suggest that as soil pH decreases, P fixation by Al and Fe
can be minimised using charcoal and sago bark ash. This is because of the alkalinity of sago bark ash
Publisher’s Note: MDPI stays neutral and the high affinity of charcoal for Al and Fe ions to impede Al and Fe hydrolysis to produce more
with regard to jurisdictional claims in H+. Thus, the optimum rates of charcoal and sago bark ash to increase P availability are 75% sago
published maps and institutional affil- bark ash with 75%, 50%, and 25% charcoal because these rates significantly reduced soil exchangeable
iations. acidity, Al3+, and Fe2+.
Keywords: phosphorus fixation; inorganic phosphorus speciation; waste management; liming
materials; carbon; functional groups; organic acids
Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and 1. Introduction
conditions of the Creative Commons
Attribution (CC BY) license (https:// Phosphorus is an essential nutrient which serves as a component of many key plant
creativecommons.org/licenses/by/ structural compounds and as a catalyst in the conversion of numerous biochemical re-
4.0/). actions in plants. It induces the development of reproductive organs in plants, pro-
Agronomy 2021, 11, 1803. https://doi.org/10.3390/agronomy11091803 https://www.mdpi.com/journal/agronomy
Agronomy 2021, 11, 1803 2 of 28
motes root growth, and enhances crop quality and maturation through accretion, transfer,
and release of energy in several cellular metabolic processes during degradation and
biosynthesis [1–3]. Phosphorus availability is limited in soils, especially in acidic soils
such as highly weathered ultisols and oxisols. This limitation is mainly because of the
abundance of Al and Fe resulting from high weathering of the soils’ minerals [4,5]. These
acidic cations tend to convert P in the soil solution to water-insoluble Fe-P and Al-P. These
water insoluble Fe-P and Al-P compounds are not readily available for plant uptake [6,7].
Orthophosphates in soil solution react with Fe and Al species to form amorphous Fe-P
and Al-P compounds, and these reactions can decrease P availability [8,9]. Phosphorus
is mostly accessible to plants at a soil pH of between slightly acidic and neutral (6.5 to
7) [10,11]. The total soil P content usually ranges from 50 to 3000 mg kg−1 (existing in
organic and inorganic forms). However, only a small proportion of the total P (usually
<1%) is available for plant uptake [10,12]. This is because in acidic soils, P is fixed by the
active forms of Al and Fe oxides and hydroxides, whereas in alkaline soils, P reacts with
Ca to form insoluble phosphate compounds [13,14].
As a solution for P fixation, farmers tend to apply a large amount of P fertilisers to
saturate the capacity of P sorption and to also ensure that there is sufficient available P
for plant uptake [15]. Excessive use of P fertilisers is not only uneconomical, but it also
has adverse effects on the environment. First, P fertilisers are largely derived from rock
phosphate, which is a non-renewable resource and major deposits are only found in a
few countries [16,17]. Second, applications of P fertilisers to soils with high P sorption
capacity can be inefficient because P largely accumulates in the soil in sparingly soluble
forms [18]. Third, when soils are saturated with P, the excess P has a greater potential to
enter water bodies through soil erosion [19], surface runoff, and leaching [20]. The losses of
P through these processes lead to eutrophication and water quality deterioration [21,22]. To
this end, studies have been conducted to improve P availability using lime [23–25]. Liming
is the conventional method to improve soil pH so as to solubilise Al and Fe to release fixed
P [26,27]. However, liming is an expensive soil conditioning approach because it is not
practical for farmers to apply higher rates of lime frequently. Furthermore, over-liming
causes calcium phosphate formation [28], a reaction which also causes P to be fixed or
makes P unavailable for optimum plant use.
In developing countries, the forestry and agricultural sectors play important roles
in their socio-economic development. This has resulted in the exponential production of
wood residues. As an example, the Malaysian timber industry generates approximately
3.4 million m3 of annual wood residues, such as sawdust, wood chips, bark, slab, and other
raw materials, with a standard 55% recovery rate [29]. Approximately 43% of the total tree
volume remains in the forest during logging operations, 13% of the sawdust is produced in
the sawmill industry and 53% of the logs are discarded as waste during processing into
plywood [30]. Therefore, the timber industry typically converts these wastes into charcoal,
briquettes, or pellets.
Furthermore, Sarawak, Malaysia is currently one of the largest exporters of sago
products in the world, with annual exports of approximately 25,000 to 40,000 tonnes to
Peninsular Malaysia, Japan, Taiwan, and Singapore [31,32]. Nevertheless, it is expected
that this value will increase every year, corresponding to the global demand, and will
consequently increase the amount of waste produced. During the processing of sago
starch, three major by-products are generated, namely sago trunk bark, fibrous pith residue,
also known as hampas, and wastewater. It is estimated that for every tonne of sago flour
produced, 0.75 tonnes of sago bark waste are created [33]. Sago bark waste is commonly
incinerated for power generation in sago mills, deposited directly into nearby rivers, or left
for natural degradation outside sago mills [34]. Annually, approximately 20,000 tonnes of
sago bark are discarded from Malaysia’s sago industry [35].
To ameliorate P fixation and to maximise the exploitation of agro-industrial waste as
higher value-added products, charcoal and sago bark ash can be used as soil amendments.
The application of soil amendments such as biochar, compost, and manures have been
Agronomy 2021, 11, 1803 3 of 28
reported to improve soil chemical properties and particularly enhancing P availability
via a reduction in P sorption sites [36–38]. Addition of these amendments to soils can
promote soil fertility and crop productivity, improve soil aggregation and structure, increase
pH buffering capacity, cation exchange capacity, soil water retention, bioavailability of
immobile nutrients, and carbon sequestration [39–41].
The highly porous structure of charcoal is resilient to biotic degradation, and this
enables it to serve as a carbon storage medium in ecosystems for a long time [42,43]. The
abundance of pores in charcoals enable air retention, hence creating an aerobic condition in
the soil [44]. Moreover, these pores are able to adsorb toxic substances such as phenolics,
Al, and Fe ions, thus avoiding the inhibition of fine roots and hyphae of arbuscular
mycorrhizae and ectomycorrhizae development [45–48]. In addition, the pores indirectly
improve nutrient retention through adsorbing and holding water [49–51]. Charcoal can
also neutralise soil pH, which is essential for crop production in acidic soils [46,50,52].
Similarly, ash can neutralise the acidity of soils because of the presence of neutralising
compounds such as calcite (CaCO3), fairchildite (K2Ca(CO3)2), lime (CaO), and magnesium
oxide (MgO) [53,54]. Demeyer et al. [55] specified that high concentrations of P, Ca, Mg, and
K in wood ash is valuable for soils which are naturally low in nutrients. In addition, wood
ash increases basic cation saturation in forest soils [56–58]. Ferriero et al. [59] found that
the concentrations of trace elements such as Mn, Zn, and B increased with the application
of wood ash. Moreover, ash is reported to enhance microbial activity in the soil, which may
favour nutrient availability [55].
It was hypothesised that combined application of charcoal and sago bark ash at the
correct amount will be able to increase P availability, at the same time fixing Al and Fe
ions. The research question to be addressed in this study is how much charcoal and sago
bark ash are needed to unlock fixed P by Al and Fe ions. The implications of including
charcoal and sago bark ash as soil amendments is not only an attempt to develop new
practices that could put agro-industrial wastes to good use, but also to provide a deeper
understanding on the mechanism involves in mitigating high P fixation of acidic soils.
A holistic understanding of the relationships and interactions of the various P pools in
soils and the numerous factors that influence P availability is essential for optimising
P management and improving P use efficiency. Therefore, this study was focused on
optimising charcoal and sago bark ash to increase P availability in acidic soils.
2. Materials and Methods
2.1. Soil Sampling, Preparation, and Selected Physico-Chemical Analyses
The soil (Bekenu Series, Typic Paleudults) used in this study was taken from an unculti-
vated secondary forest of Universiti Putra Malaysia Bintulu Sarawak Campus (UPMKB)
on geographical coordinate of 3◦12′20′′ N, 113◦04′20′′ E (Figure 1). This soil was selected
because it is commonly cultivated with different crops in Malaysia although it is charac-
terised by high P-fixing because of high Al and Fe contents. The area has an elevation of
27.3 m, an annual rainfall of 2993 mm, a mean temperature of 27 ◦C, and a relative hu-
midity of approximately 80%. The soil was randomly sampled with specifications of
1 m length × 1 m width at depth of 0–20 cm using a shovel. Ten sacks of soil were sampled,
each containing approximately 10 kg of soil. Thereafter, the soil was air-dried, crushed
manually, and sieved through a 2 mm sieve.
The soil was analysed for soil bulk density using the coring method [60]. Soil texture
was determined using the hydrometer method [61]. Soil pH in water and KCl and electrical
conductivity (EC) were determined at a ratio of 1:2.5 (soil:distilled water/KCl) using a
digital pH meter and EC meter [62]. Soil total carbon was calculated as 58% of the organic
matter determined using the loss on ignition method [63]. Total N was determined using
the Kjeldhal method [64]. The soil cation exchange capacity (CEC) was determined using
the leaching method [65] followed by steam distillation [64]. Soil exchangeable acidity, H+,
and Al3+ were determined using the acid-base titration method [66].
Agronomy 2021, 11, 1803 4 of 28
Agronomy 2021, 11, x  4 of 28 
 
 
Figure 1. Aerial view of location where soil was sampled for incubation study in Universiti Putra Malaysia Bintulu Sara-
wak CampFuigsu, Mrea1la. yAsiear.i al view of location where soil was sampled for incubation study in Universiti Putra
Malaysia Bintulu Sarawak Campus, Malaysia.
The soil was analysed for soil bulk density using the coring method [60]. Soil texture 
Soil total Pwwasa sdeetxetrrmacitneedd uussiinngg tthhee hayqduraormeegtiear mmeetthhoodd [[6617]].. STohile paHq uina wreagtiear saonldu KtioCnl and electri-
was prepared bcyalm coinxidnugctcivointyce (nEtCra) twedereH dCeltearnmdinceodn acet na trraattieod ofH 1N:2.O5 3(saotila:drisattiiloledo fw3a:1te.rA/KCl) using a 
2 g sample of dsoigilitawl apsHw meeitgehr eadnda EnCd mpleatceer d[62in].t Sooial t2o5ta0l mcaLrbocon nwicaasl cafllacsukla, teadft ears 5w8%hi cohf the organic 
20 mL of aqua rmegatiatesr odleutteiromniwneads uasdindge dth. eT lhoesrse oanft eigr,ntihtieons umseptehnosdi o[6n3w]. aTsothael aNte wdaosn daetheormt ined using 
plate until the tshoel uKtjieolndhtaulr mneedthcolde a[6r.4]T. Thhees suosipl ecantsioionn exwcahsanfiglete craepdacuistyin (gCEinCt)o waa1s 0d0etmerLmined using 
volumetric flaskthaen ledadchiliuntge md etothtohde [r6e5q] ufoirlleodwveodl ubym setewamith ddisitsiltliallteiodnw [6a4t]e.r S. oSiol ielxacvhaainlgabealeblPe acidity, H+, 
and exchangeable cations (K+, Ca2+ 2+ + 2+ 2+and Al3+ were determ,inMegd us, iNnga th, Me ancid,-baansde Ftietrat)iowne mreeethxtorda c[t6e6d]. using the
Mehlich No.1 doublSeoailc tiodtaml ePt hwoads [e6x8tr]a. cTthede udsoiunbg ltehaec aidqusao lruegtiioan m(methixotdu r[6e7o].f T0h.0e5 aMquHa Crelgia solution 
and 0.025 M H2wSOas4 )pwreapsaprerdep bayr emdixbiyngm cioxnincgen4t.r1a2temd LHoCfl caonndc ecnotnrcaetnedtraHteCdl HwNithO31 a.4t0 am raLtioo fof 3:1. A 2 g 
concentrated H2sSaOm4plien oaf1 s0o0i0l wmaLs vwoeliugmheedtr aicnflda pslkacaendd idnitlou ate 2d5t0o mthLe croenqiucairle fdlavsko,l uamfteer wihthich 20 mL of 
distilled water. aAqu5ag rseagmiap sloeluotfiosoni wl wasa sadwdeeidg.h Tehdearenadftperla, cthede siunstopeanpsiloanst wicavsi ahle,aatfetder own ha ihchot plate until 
20 mL of doubtlheea scoildutsionlu ttuiornedw calseaard. Tdheed s.uAspfetenrswioanr wdsa,s tfhiletesrueds puesninsgio intow aa 1s0s0h makLe vnolautmetric flask 
180 rpm for 10amndi nd.iluTthede tsou tshpee rnesqiuoinrewd avsolfiulmteer wedithin dtoistaillpedla wstaictevr.i Saol iul asivnagilafiblltee Pr  apnadp erx.changeable 
Series of extractcaantitosnws e(Kre+,u Csae2d+, tMo gfr2a+,c Ntioa+n, aMtenp2+o, aonlsdo Ffei2n+)o wrgearne iecxPtrafoctlleodw uisnigngt hthees eMqeuhelnicthia Nl o.1 double 
extraction methaocidd dmeescthriobde d[68b]y. TKhueo d[o6u9b].leL aocoisde slyolsuotilounb l(emPix(tSuorel- Pof) 0w.0a5s Mre mHoCvl eadndu s0i.n0g25 M H2SO4) 
1 M NH4Cl. Alwumasi pnriuepma-rbedo ubnyd mPix(iAngl- 4P.1)2w masL soefp caornacteendtrfartoemd HirColn w-bitohu 1n.4d0P m(LF eo-fP c)ouncseingtrated H2SO4 
0.5 M NH4F at ainp aH 10o0f08 m.2,Lt hveonluFmee-Ptriwc falsasrke manodv eddilutseidn gto0 t.1heM reNquaiOreHd. vRoeludmucet awnitths odliusbtilleled water. A 
P (Red-P) was e5x tgr ascatmedplues oinf gso0il. 3wMas swodeiiguhmedc iatnradt epl(aNcaed3C in6Hto5 aO p7l)a,s1tiMc vsiaold, iauftmerb wichaircbho 2n0a mteL of double 
(NaHCO3), andacsiodd sioulumtiodnit hwiaosn adtede(Nd.a A2Sft2eOrw4)a.rdCsa, ltchieu msu-sbpoeunnsidonP w(Casa -sPh)akwenas aet x1t8r0a crptemd for 10 min. 
using 0.25 M HT2ShOe 4s,uwspheenrseiaosn fworaso fcicltleurdeedd inPto( Oa cpclla-sPti)c,  0v.i1alM usNinagO fiHltewr paaspuesre. dSe. ries of extractants were 
Soil total Pu, Msedeh tloic fhr-aPc,tiaonndatien oprogoalns iocfP incoorngcaennitcr aPt ifoonllowweirnegd tehtee rsmeqinueedntuiasli nexgtrUaVct-iVonIS method de-
Spectrophotomsecterirb(ePde rbkyi nKEuolm [6e9r]L. aLmoobsdelay2 s5o,lWuballet hPa (mSo, lM-PA) ,wUaSs Are)matov88ed2  numsinwg a1v Mele NngHth4Cl. Alumin-
after a blue coloiuumr w-baosudndev Pe l(oApl-ePd) uwsaisn gsetphaeramteodl yfrbodmen iruomn-bboluuendm Pe t(hFoed-P[)7 u0s]i.nAg c0i.d5 Mm oNlyHb4-F at a pH of 
date stock solut8io.2n, t(hReena gFeen-Pt wA)asa nredmaosvcoedrb uicsiancgi d0.s1t Moc kNsaoOluHt.i oRned(Ruectaagnetn stoBlu)bwlee Pre (Rperedp-Par) ewdas extracted 
for the blue coluosuirngd e0v.3e Mlop smodeinutmp criotrcaetde u(Nrea.3AC6Hst5aOn7d),a 1r dMP sosodliuutmio bnic(asrtabnondaatred (NsoalHutCioOn3)1, )and sodium 
and standard sdolituhtiioonna2te w(Neare2Sp2Ore4)p. aCraeldciuamnd-buosuendd tPo (pCrae-pP)a wreaws eoxrtkrainctgedso ulsuitnigo n0s.2r5a Mng Hin2SgO4, whereas 
from 0 to 0.6 ppfomr .ocIcnluthdiesdp Pr o(Ocecscsl-,P1),t 0o.16 Mm LNaoOf Hst awnadsa urdsesdo. lution 2 was pipetted into a
50 mL volumetric flaSsokil ctoontatla iPn, iMngeh8lmichL-Po,f aRneda gineonrtgBanainc dPd cioluntceednttroattihoen rweqeurei rdedetevromluinmede  using UV-
with distilled wVaItSe rS.pAecfttreorpwhaortdosm, e8temr L(PoefrkRinea EglemnetrB Lawmabsdpai p2e5t, tWedalitnhtaoma, dMifAfe, rUenSAt 5) 0atm 88L2 nm wave-
volumetric flaskle, nagfttehr awftheirc ah bthluees caomlopuler wwaass daedvdeeldopdeedp uensidnign gthoe nmtohleybindteennusimty bolfueth me ebtlhuoed [70]. Acid 
colour to be demveolloypbedda.teT shtoecsko sluoltuiotinonw (aRsedagileuntte dA)t and ascorbic acid stock solution (Reagent B) were prepared for the blue colour developmoetnhte preroqcueidreudrev. oAl usmtanedwaritdh Pd issotliullteiodn (standard 
water. Soil exchsaonlugteioabnl 1e) caantdio sntsanwdearred dsoeltuertimonin 2e wd eursei npgreaptaormedi canabds uosrepdt itoon psrpepeactrreo wmoertkriyng solutions 
(AAS) (Analystr8a0n0g,iPnegr fkrionmE 0lm toe r0, .N6 porpwma. lIkn, CthTis,  UprSoAce).ssT,h 1e tpo h6y msiLco o-cf hsteamndicaarldp sroolpuetriotine s2 owf as pipetted 
the soil used initnhtios ap r5e0s emnLt  svtoulduymweterirce fwlaistkh icnonthtaeinrainngg e8 rmepLo ortfe RdebaygePnat rBa manadn adniltuhtaend [t7o1 ]t,he required 
except for soil tevxotluurme.eT whieths edliescttielldedp whyastiecro. -Achfteemrwicaarldps,r o8 pmeLrt ioefs Roefatgheensto Bil waraes spuipmemtteadri sinetdo a different 
in Table 1. The percentages of the inorganic P fractions in the soil before the incubation
 
Agronomy 2021, 11, 1803 5 of 28
study are summarised in Table 2, where the order of the P fraction was Fe-P > Occl-P >
Al-P > Ca-P > Red-P > Sol-P.
Table 1. Selected physico-chemical properties of the soil used in incubation study.
Property Value Obtained Standard Range *
pH (water) 4.61 4.6–4.9
pH (KCl) 3.95 3.8–4.0
EC (µS cm−1) 35.10 NA
Bulk density (g cm−1) 1.25 NA
Total carbon (%) 2.16 0.57–2.51
Total N (%) 0.08 0.04–0.17
Total P (mg kg−1) 23.65 NA
Available P (mg kg−1) 1.13 NA
CEC 4.67 3.86–8.46
Exchangeable acidity 1.15 NA
Exchangeable Al3+ 1.02 NA
Exchangeable H+ 0.13 NA
Exchangeable K+ −1 0.06 0.05–0.19cmol kg
Exchangeable Ca2+ 0.02 0.01
Exchangeable Mg2+ 0.22 0.07–0.21
Exchangeable Na+ 0.03 0.01
Exchangeable Mn2+ 0.01 NA
Exchangeable Fe2+ 1.09 NA
Sand (%): 71.9 Sand (%): 72–76
Silt (%): 13.5 Silt (%): 8–9
Soil texture Clay (%): 14.6 Clay (%): 16–19
Sandy loam Sandy clay loam
Note: * Standard range subjected to the soil development by Paramananthan [71]; NA: not available; Available P:
P that was extracted using Mehlich 1 method (Mehlich-P).
Table 2. Percentages of inorganic phosphorus speciation in soil before incubation study.
Inorganic Phosphorus Percentage (%)
Loosely soluble phosphorus (Sol-P) 0
Aluminium bound phosphorus (Al-P) 11
Iron bound phosphorus (Fe-P) 67
Reductant soluble phosphorus (Red-P) 3
Calcium bound phosphorus (Ca-P) 7
Occluded phosphorus (Occl-P) 12
Total 100
2.2. Charcoal and Sago Bark Ash Characterisation
The charcoal used in this study was obtained from Pertama Ferroalloys Sdn Bhd,
Bintulu, Sarawak, Malaysia, whereas the sago bark ash was purchased from Song Ngeng
Sago Industries, Dalat, Sarawak, Malaysia. Afterwards, the amendments were analysed
for pH in water and in KCl, EC [62], available P [68,70], and exchangeable K+, Ca2+, Mg2+,
Na+, and Fe2+ [68]. The results of these analyses are presented in Table 3.
Agronomy 2021, 11, 1803 6 of 28
Table 3. Selected chemical properties of charcoal and sago bark ash.
Property Charcoal Sago Bark Ash
pH (water) 7.74 9.99
pH (KCl) 7.31 9.66
EC (dS m−1) 0.27 5.75
Available P (mg kg−1) 31.25 55.83
Exchangeable K+ 3.67 23.33
Exchangeable Ca2+ 11.71 16.77
Exchangeable Mg2+ cmol kg−1 3.37 3.57
Exchangeable Na+ 0.43 1.51
Exchangeable Fe2+ 0.15 0.03
Note: Available P: P that was extracted using Mehlich 1 method (Mehlich-P).
2.3. Incubation Set Up
A laboratory incubation study was conducted in the Soil Science Laboratory of
UPMKB. A 1 kg sample of soil (from the 2 mm bulked soil sample) was weighed in
a polypropylene container. Egypt rock phosphate, charcoal, and sago bark ash were added
and thoroughly mixed according to the treatment evaluated in this present study. The
samples were moistened to 60% of moisture content based on the soil field capacity. The
lids of the polypropylene containers were perforated to allow good aeration. The samples
were incubated at room temperature (26 ◦C) for 30, 60, and 90 days. The recommended
rate of the P fertiliser used was 60 kg P2O5 ha−1 (214 kg ha−1 ERP). This rate was based on
the standard recommendation for maize (Zea mays L.) cultivation [72]. Maize was chosen
as the test crop because of its sensitivity, which can reflect nutrient recovery, uptake, and
efficiency and rapid response towards nutrient deficiency. The rate at which the fertilisers
were applied in the incubation study was scaled down to a per plant basis (based on
planting density of 27,777 plants ha−1), which was equivalent to 7.7 g of ERP plant−1. The
amounts of the amendments used were deduced from the literature (charcoal [73,74] and
sago bark ash [75–77]) where 10 and 5 t ha−1 equivalent to 51.4 and 25.7 g, respectively, in
1 kg of soil per container. The charcoal and sago bark ash rates were varied by 25%, whereas
the ERP rate was fixed at 100% of the recommendation rate in all treatments except for
T1 (no ERP applied). The treatments evaluated in this present study are summarised
as follows:
T1: Soil only
T2 Soil + ERP
T3 Soil + ERP + 51.4 g charcoal
T4 Soil + ERP + 25.7 g sago bark ash
T5 Soil + ERP + 51.4 g charcoal + 25.7 g sago bark ash
T6: Soil + ERP + 38.6 g charcoal + 19.3 g sago bark ash
T7: Soil + ERP + 25.7 g charcoal + 19.3 g sago bark ash
T8: Soil + ERP + 12.9 g charcoal + 19.3 g sago bark ash
T9: Soil + ERP + 38.6 g charcoal + 12.9 g sago bark ash
T10: Soil + ERP + 25.7 g charcoal + 12.9 g sago bark ash
T11: Soil + ERP + 12.9 g charcoal + 12.9 g sago bark ash
T12: Soil + ERP + 38.6 g charcoal + 6.4 g sago bark ash
T13: Soil + ERP + 25.7 g charcoal + 6.4 g sago bark ash
T14: Soil + ERP + 12.9 g charcoal + 6.4 g sago bark ash
2.4. Experimental Design and Statistical Analysis
The treatments were arranged in a completely randomised design (CRD) with three
replications. Normality test was used to determine if the data set is well-modelled by a
normal distribution. Analysis of variance (ANOVA) was used to detect treatment effects,
whereas treatments means were compared using Tukey’s Studentized range (HSD) test at
p ≤ 0.05. The statistical software used was Statistical Analysis System (SAS) version 9.4.
Agronomy 2021, 11, 1803 7 of 28
3. Results
3.1. Effects of Amending Egypt Rock Phosphate with Charcoal and Sago Bark Ash on Selected Soil
Chemical Properties
The effects of treatments on soil total carbon (TC) at 30, 60, and 90 days of incubation
(DAI) are presented in Figure 2. There was no significant difference in TC for T1 and T2,
regardless of incubation period. The treatment with the sago bark ash alone (T4) demon-
Agronomy 2021, 11, x FOR PEER REVIEW strated lower contribution towards TC. At 30 DAI, the effec8t sof o28f T3, T5, and T12 on TC
 
were similar but significantly higher than those of T1, T2, T4, T6, T7, T8, T9, T10, T11, T13,
and T14. Although T5 had higher content of TC, the effect was not significantly different
Amcoomngp taher etdreattomTen9tsa, tT610 hDadA thIea hnidghTes3t asonild eTxc1h2anagte9ab0leD FAe2I+ .aTt h30r,o 6u0g, ahnodu 9t0t h e28i8ncubation study, the
DAI (FigTuCreo 8f).t hUepotnr eaaptpmliceantion of charcoal and sago bark ash, soil exchangeable Fe
2+  289
reduced. There was no significatnst wdififtehre2n5ce% inc shoailr ecxochaaln(gTe8a,blTe 1F1e2,+ abnetdweTe1n4 T)2w anads ,Ts3i, milar irrespective of the 290
irrespecatimve oouf inntcuobfatsiaong otimbea.r k ash used.  291
  292
Commented [PDBJ10]: Please, this is a new 
Figure 2 because the axis name has been changed 
from “soil total organic carbon” to “soil total 
carbon” 
  293
Figure 2. Effects o f treatments on soil total carbon after thirty, sixty, and ninety days of incu 2b9a4tion, where T1:
Figure 2. Treatments on soil total organic carbon after thirty, sixty, and ninety days of incubation, where T1: soil  295
soil alone, T2: Egypt r Commented [PDBJ11]: Please change “total alonoe,c Tk2: pEhgyopst prohcka ptehoasplhoantee a,loTne3, :T3E: Eggyyptt rorcokc pkhopsphhoatse p+ h10a0t%e c+har1co0a0l,% T4: cEhgyaprtc rooackl ,phTo4sp:haEteg +y p t29r6ock phosphate +
100% sago bark ash, a1n00d% Tsa5g:oE bgarykp atshr,o acnkd pT5h: oEsgpypht aroteck+ ph1o0sp0h%atec h+ a10r0c%o aclha+rc1oa0l 0+% 10s0%ag soagbo abrakrk aasshh,, TT6:6 E: gEygpty rpoctkr o c2k97phoorsgpahnaict eca+rb7o5n%” to “total carbon” 
phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash,  298
charcoal + 75% sago Tb8a: Erkgypats rhoc,kT p7h:osEpghaytep +t 2r5o%c ckhaprchoaol s+p 7h5%a tseag+o b5ar0k% ashc,h Ta9:r Ecgoyaplt r+oc7k 5p%hosspahagteo +b 7a5%rk chaasrchoa, lT + 85:0%E g y2p99t rock phosphate
+ 25% charcoal + 75%sagsoa bgarok absha,r Tk10a: Esghy,ptT ro9c:k Ephgoyspphtater o+ c50k%p chhaorcsopalh + a5t0e% s+ag7o 5b%ark cahsha, Trc11o: aEgly+pt 5ro0c%k phsoasgphoateb +a 2r5k% as h30,0T10: Egypt rock
charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock  301
phosphate + 50% chaphrocsopahalte+ + 50% chsaarcgoaol +b 2a5r%k sagsoh b,arTk 1as1h:, aEndg Ty1p4:t Ergoypctk ropckh pohsopsphattee + +25%2 5ch%arccohal a+r 2c5o%a slag+o b5a0rk%  s3a0g2 o bark ash, T12:
Egypt rock phosphataesh+. M7e5a%ns wchitha rdcifofeareln+t le2tt5e%r(s) swaigthoin bthaer ksamaes hin,cuTb1at3io:nE pgeryiopdt inrodiccaktep shigonisfipcahnta dteiffe+re5nc0e% betcwheaenr co a30l3+ 25% sago bark
treatments by Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.  304
ash, and T14: Egypt r ock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter (3s0)5within the same
incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e.,
a > b > c. Bars represent the mean values ± SE.
Figures 3 and 4 suggest that the treatments without soil amendments (T1 and T2) had
significantly lower pH compared with the treatments with the soil amendments (T3, T4,
T5, T6, T7, T8, T9, 10, T11, T12, T13, and T14). At 30 and 60 DAI, the soil pH for T5 was
significantly higher than other treatments with charcoal and sago bark ash. At 90 DAI,
the effect of the treatment with sago bark ash alone (T4) on soil pH was not significantly
different compared to the treatments with the combined use of charcoal and sago bark ash
at 100% (T5) and the combination of charcoal and sago bark ash at 75% (T6). Among the
Figure 3. Ttrreeaatmtemntse onn tssoilw pHit ihn wtahteer asfoteri lthairmty, esinxtydm
  306
, ande nnintesty,  dthayes otfr iencautbmatioenn, wthwerei tTh1: scohil aalronceo, a l3a07lone (T3) had lower
T2: Egypt srocikl phoHsp,hratee galaonred, lTe3:s Esgyopft rioncck uphboaspthiaoten + p10e0r%i ochdar.coal, T4: Egypt rock phosphate + 100%  308
sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate +  309
75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock  310
phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash,  311
T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50%  312
sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50%  313
charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with  314
different letter(s) within the same incubation period indicate significant difference between treatments by Tuk-  315
ey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.  316
  317
 
Agronomy 2021, 11, x  8 of 28 
 
Agronomy 2021, 11, x  8 of 28 
 
treatments with the soil amendments, the treatment with charcoal alone (T3) had lower 
soil pH, regardless of incubation period. 
Agronomy 2021, 11, 1803 8 of 28
treatments with the soil amendments, the treatment with charcoal alone (T3) had lower 
soil pH, regardless of incubation period. 
 
Figure 3. Effects of treatments on soil pH in water after thirty, sixty, and ninety days of incubation, 
where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% charcoa l, 
FTi4g: uErgey 3p. tE rfofecckt sp ohfo tsrpehaatmtee +n t1s0 o0n% s soaigl po Hba irnk w ash, and T5: Egypt rock phosphate + 100% charcoal + Figure130.0E%ff escatgs oo fbtarerakt masehn,t sTo6n: EsgoiylpptH roinckw patheorsapftheartteh
aitretry ,asfitxetry ,thanirdtyn,i nsiexttyyd, aaynsdo nf iinnety days of incubation, 
where T1: soil alone, T2: Egypt rock phosphat e+  a7l5o%ne c, hTa3r:c Eoagly +p t7 5ro%c ks apghoo bsa
crukb aatsihon, ,Tw7:h EergeyTp1t: rsoocilka lone,
T2: Egyppht rock phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt roc
pkhpahteo s+p h1a0t0e%+ 1c0h0a%rcsoaaglo, bark
ash, anTd4T:
o Espghyaptte r +o c5k0 %p hcohsaprchoaatel  ++ 7 150%0 %sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago 
bark5: aEsghy,p Tt9ro: cEkgpyhpot srpohcakt ep+ho10s0p%hacth
 saarcgooa lb+ar1k0 0a%shs,a gaondba Trk5:a Eshg,yTp6t: Erogcykp tphosphate + 100% charcoal + 
100% sago bark ash, T6: Egypt rocek  +p 7h5o%sp chhaaterc +o a7l5 +% 5 c0h%a rscaogaol  b+a 7r5k% a ssh
r,o Tck10p:h Eosgpyhpatt ero+c7k5 p%hcohsaprchoaatle+ 75%
sago ba+r 5k0a%sh c,hTa7r:cEogaylp t rock phosphate + 50% charcoal + 75% sago bark ash, T8: E
aggyop tbraorckk apshho, sTp7h:a Eteg+yp25t %rocchka rcoal
+ 75% spahgoosbpahraktea s+h 5, T0%
+  5c0h%ar scaogaol  +b 7a5rk% a ssahg, oT b11a:r kE gayshp,t  Tro8:c kE gpyhposphate + 25% charcoal + 50% sago bark ash, 
T12: Egypt rock9 :pEhgoysppthraotcek +p h7o5s%p hcahtear+co7a5l% +c 2h5a%rc osaalg+o50
t %roscakg pohboasrpkhaashte, T+ 1205:%E gcyhpatrcroocakl +p h7o5s%p hsago 
bark ash, T9: Egypt rock phosphate + 75% charcoal + 50 %ba srakg aos bha, rTk1 a3s: hE,g Ty1p0t:  rEogcykp pt hroocskp hpahtoe s+p h5
a0te%+ 50%
charcoaclh+ar5c0o%als a+g 2o5b%ar ksaagsoh, bTa1r1k:  Eagsyhp, tarnodck Tp1h4o: sEpghyate + 25% charcoal + 50% sago bark ash, T12: Egypt rock pho
astpeh ate +
75% ch+a r5c0o%al c+h2a5r%cosaalg +o 5b0a%rk saasgho,  Tb1a3r:kE agsyhp,t Tr1o1ck: Epghy
ppt tr orocckk p phhoosspphhaatete + + 2 255%% c chhaarrccooaall  ++  2550%%  ssaaggoo  bbaarrkk ash. 
Means with different letter(s) within the samoes pinhactueb+at5i0o%n pchearriocoda lin+d2i5c%ates asgigonbiafrickaansth d, aifnfderTe1n4c:eE
 agsyhp,t rock
phosphTa1te2:+ E2g5y%pct hraorccko aphosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 
s5 b0%e- 
tcwhaerecno atrl e+a t2m5%en stas
l a+c2c5o%rdsianggo tboa rTkuaksehy. ’Ms eHanSsDw tietsht daitf fpe r≤en 0t.0le5t,t eir.e(s.), wa i>th bin >t hc.e Bsaamrse rienpcurebsation pego bark ash, and T14: Egypt r ent the
r imodeainnd icate
significvaanltudeisff e±r eSnEc.e s between treatments according to Tuke
oyc’ks HphSDostpehstaattep +≤ 250%.05 c, hi.ea.r,cao>alb +> 2c5.%Ba srsagreop breasrekn tatshhe. mean
valuesM±eSaEn. s with different letter(s) within the same incubation period indicate significant differences be-
tween treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean 
values ± SE. 
 
FigureF4i.gEufrfeec 4ts. oEfffterecatstm oef nttrseaotnmsoeniltps Honin spooilt apsHsi uimn pcholtoarsisdieumaft ecrhltohriritdye,  saixftteyr,  atnhdirtnyin, estiyxtdya, yasnodf ninincuebtya tdioany,sw here
T1: soiol fa lionnceu, bTa2t:ioEngy, pwthroecrke pTh1o: sspohila taeloalnoen,e T, T23: :EEggyypptt rroocckk pphhoosspphhaatete+ a1l0o0n%e,c Tha3r: cEoagly, pTt4 :rEogcky ppthroocskphpahtoes p+h ate +
100% s1Fag0igo0u%bra erc kh4aa. srEhcf,ofaeancl,dt sT To45f::  tEErggeyyaptpmtt reornockctskp  ohpnoh ssoposhipal htpeaH+te 1 i0n+0  1%p0oc0tha%as rsscioauagmlo+  cb1ha0lr0ok%r iadssaehg a,o fabtneardr kt hTais5rh:t ,yET,g 6sy:ixpEtgty yr,p oatcnrkdo cp nkhipnohseoptyshp adhtaaety e+s+  75%
charco1oal0f +0i%n7c5 uc%hbasaartcigooonab,l  a+wr k1h0ae0srh%e,  TTsa71:g: Eosog byilap ratklro oancskeh,, p TTh26o::s  pEEhggayytppett+  rr5oo0cc%kk  pcphhaoorscspophahlaa+ttee7 + 5a %7lo5sn%aeg ,co hTba3ar:r ckEogaasyl h+p, t7T 5r8o%: cE ksga ypgphoto rbsoapcrkhkap atheso h+s,p  hate
+ 25% T1ch07a0: r%Ecog cayhlpa+tr 7cr5oo%aclk,s  aTpg4ho:o Ebspagrhykapattes r h+o, cT5k90 :%pEh gcohyspaptrhcraotacekl  ++p  1h70o50s%p%h  sasataeggo+o  b7ba5a%rrkk c ahasashrhc,, o Taa8nl :d+ E 5Tg05y%:p Ets agrgyoocpktb  arprohkcokas spphhh, aTot1sep0 :h+E a2gt5ey %p+t  rock
phosphc1ah0t0ae%r+c oc5ah0la% +r cc7oh5aa%lr c+ os 1a0gl 0+o% 5b 0as%arkgs oa sgbhoa,r bkTa 9rak:s Eha,gs Thy,6pT:t  E1r1go:ycEkpg tpy rhpootcskrpo pchkhaotpesh p+oh s7pa5ht%ea t+ ec 7h+5a%2r5c %ochacla hr+ac 5orc0ao%la +l  s+7a5g5%0o%  sbaasgarokg  obaasbhrakr, k Taas1hs0h,:  , T12:
Egypt ETrog7c:yk Epptgh yroopscptk hr oaptcheko+ spp7h5ho%astpcehh +aa r5tce0o %a+l  5+c0h2%a5r% ccohsaaalgr +co o5ba0al%r k+  sa7as5hg%,oT  bs1aa3gr:koE  gabysahprt,k Tr oa1cs1kh: ,pE hTgo8ys:p Eth graoytecpk+t  pr5o0h%coksc pphhaharoctseop a+hl +2a5t2e%5 +% c 2hs5a%gr-o bark
ash, anccdohTaalr1 c+4o: 5aE0lg %+y  ps7ta5rg%ooc  skbaapgrhoko  abspsahrk,a Tt ea1s+2h:2, E 5Tg%9y:c pEhtag rryocpcokta l rp+ohc2ok5s %pphhsoagtsepo +hb a7atr5ek% +a  sc7h5.a%Mrc eocahanla sr+cw 2o5iat%hl + ds ia5ffg0eo%re b nsatarlgkeot at ebsrha(s,r )kTw 1a3ist:hh E,i ngTyt1hp0et:  same
incubarEtoigocynkp pte hrrooiocsdkp hipnahdtoeic s+ap t5eh0as%tieg  nc+hi fi5ac0rac%not acdlh i+af fr2ec5roe%anl c se+as g5bo0e %btwa sreakegn aost brhea,a ratkmn dae snTht1s, 4Ta:c 1Ec1og:r yEdpginty grpottco rkoT pcukhk oepyshp’sohsHaptSheD a+t te2e 5s+t% 2a 5tc%hpa ≤crhco0aa.r0-l5 , i.e.,
a > b >+cco .2aB5l%a +r s 5sr0ae%gpor se baseganrokt bt ahaserhkm.  aeMsahne,a vTna1sl2u w:e Esitg±hy SpdEtif .rfoercekn pt hleotstperh(ast)e w +i 7th5i%n  cthhea rscaomale + i n2c5u%b saatigoon b paerrki oadsh i,n Td1i3ca: tEeg syipgt- 
nroifcikc apnht odsipffhearteen +ce 5s0 b%e tcwheaercno tarle +a t2m5e%n tssa gacoc boardrkin ags hto,  aTnudk Tey1’4s:  HEgSyDp tte rsot cakt  pp h≤o 0s.p0h5,a it.ee .+,  a2 5>% b  c>h ca.r Bcoarasl  
r+e 2p5r%es esnagt oth bea mrke aansh v. aMlueeasn ±s  SwEi.t h different letter(s) within the same incubation period indicate sig-
nificant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
 
 
Agronomy 2021, 11, x  9 of 28 
 
Agronomy 2021, 11, 1803 9 of 28
The interaction between the time of incubation and treatment significantly affected 
soil exchangeable acidity (Figure 5). Among the treatments, T1 recorded the highest soil 
exchangeable acidity foTllhoewinetder abcyti oTn2b. eStwoiele enxtchheatinmgeeoafbilnec uabcaidtioitnya inndctrreeaatsmeden at ss igthneifi acamntolyuanftf ected
of sago bark was resdouilceexdch farnogmea b1l0e0a%cid titoy 7(F5i%gu,r e505%). A, amnodn g2t5h%e t.r eTahtmroeuntgsh, To1urte cthored eindctuhebahitgiohnes t soil
study, the effect of ethxceh atrnegaeatmble nacti dwityithfo lclohwaerdcobaylT a2l.oSnoiel eaxtc hthaneg reabtele oafc id1i0ty0%in c(rTea3s)e donas sthoeila mexo-unt of
changeable acidity wsaagso bnaortk swigasnriefdicuacnedtlfyro dmif1f0e0r%entot c7o5%m, p50a%re, adn tdo2 t5r%e.aTtmhroeungth wouitthth tehinec cuobamtiboni-study,
nation of charcoal atth 7e5e%ffe,c t5o0f%th, eatnreda t2m5e%nt awnitdh cshaagrcoo ablaarlkon aesaht  tahte 2ra5t%e o (fT10102%, T(T133),o annsdoi lTe1x4ch).a nAg eable
acidity was not significantly different compared to treatment with the combination of
similar trend was alcshoa frocouanl d 3+at i7n5 %so, i5l0 e%x,cahnadn2g5e%abanled Asalgo (bFairgkuarseh 6a)t. 2S5oil exchangeable Al3+% (T12, T13, and T14). A osfi milar
soil alone (T1) and EtrRenPd awloans ea l(sTo 2fo)u wnderien soigilneixfcihcangtelyab hleigAhl3e+r( tFhigaunr eth6)o. sSeo iwl eixtchh acnhgaeracbolae lA al3n+do f soil
sago bark ash. Betwaeleone T(T11 a)nandd TE2R, PTa2l odneem(To2)nwsterraetseidgn sifiigcannitfliycahnigthlyer ltohwanetrh ossoeilw eixthchchaanrcgoeaal banled sago
b 3+Al3+. Regardless of tharek ianshc.uBbeatwtioeenn pT1erainoddT, 2s,oTi2l deexmcohnasntrgaeteadbslieg nAifilc3+a nftolyr ltohw3+ e
e rtrseoialtemxcehnant gweaibthle Al .
sago bark ash aloneR (eTg4a)rd less of the incbark aswh aalso nneo(Tt 4s)igwn
uibfiactaioas not n
ntlpye rdioidff,esrosignificantlye
ilnetx ccohamnpgeaarbelde  Atol  thfoer ttrheeattrmeaetment with sagodifferent compared to the treatmenntstws iwthicthha rcoal
charcoal and sago baanrdk saasgho.b ark ash.
 
FiFgiugreu5re. E 5ff.e cEtfsfoefctrse aotmf etrnetsatomn seoniltse xochna nsgoeial belexcahciadnitygeaaftberleth airctyid, siitxyty a, aftnedr ntihneirtytyd,a syisxotfyi,n acunbda tinoinn,ewtyhe rdeaTy1s: soofi l
alionnceu, Tb2a:tEiognyp, twrohcekrpeh Tos1p: hsaotiel aalolonne,eT, 3T: 2E:g Eypgtyrpoctk rpohcoks pphhaotesp+h1a00te% aclhoanrceo,a Tl,3T:4 E: Eggyypptt rroocckkp phhosopshpahtea+te1 0+0 1%0s0a%go 
bacrhkaarscho, aanl,d TT45:: EEggyyppt rto rcokcpkh opsphhoastpe h+a1t0e0 %+ c1h0a0rc%oa ls+ag1o00 %basrakg oabsahr,k aanshd,  TT65: :E gEygpytprotc kropchko spphhaotsep+h7a5t%e c+h a1r0co0a%l + 
75c%hasargcooabal r+k a1s0h0,%T7 :sEaggyop tbraorckk pahsohs,p Tha6t:e E+g5y0%ptc hroarcckoa pl +ho75s%phsaagtoe b+a r7k5a%sh ,cTh8a:rEcgoyaplt +ro 7ck5%ph ossapghoa teba+r2k5 %aschha, rTco7a: l
+ E75g%ypsatg roobcakr kphasohs,pTh9:aEteg y+p 5t0r%oc kchpahrocspohaal t+e 7+57%5% sachgaor cboaarlk+ a5s0h%, sTa8g:o Ebgayrkpat srho,cTk1 0p:hEogsyppht raotcek +p 2h5o%sp hcahtaer+co50a%l 
ch+a r7c5o%al  +sa50g%o sbaagrokb aarskha, sTh9, T: E11g: yEpgyt prtorcokck pphhoosspphhaatete+ +2 57%5%ch acrhcaoarlc+oa5l0 %+ 5sa0g%o  bsaargkoa sbha, rTk1 2a:sEhg,y Tpt1r0o:c Ekgpyhopstp rhoactek+ 
75p%hcohsaprhcoaatle+ +2 55%0%sa gcohbaarrckoaaslh +, T 5103%: E gsyapgtor obcakrpkh oassphh, aTte1+1:5 0E%gychpatr crooaclk+ p25h%osspaghoabtea r+k a2s5h%, a ncdhaTr1c4o: Eagl y+p 5t r0o%ck 
phosphate + 25% charcoal + 25% sago bark ash.. Means with different letter(s) within the same incubation period indicate
sigsanigfioca bntadrkiff earsehnc, eTs 1be2t:w Eegenytpret artmoceknt spahcocosrpdhinagteto +T u7k5e%y’s cHhSaDrcteosat la t+p 2≤50%.0 5s,ai.ge.o,  ab>abrk> ac.sBha,r sTr1e3p:r eEsegnytpthte rmoecakn 
vapluheoss±phSEa.te + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 
25% sago bark ash.. Means with different letter(s) within the same incu+ bation period indicate sig-The effects of treatments on soil exchangeable H are demonstrated in Figure 7. Soil
nificant differences beetxwceheanng teraebaltemHe+ntfso raTcc1owrdasinsgig tnoifi Tcuanktelyy’hsi gHhSeDr t hteasnt tahto ps e≤o 0f.T052,, Ti.3e,.,T a4 ,>T b5 ,>T c6., BTa7r, sT 8, T9,
represent the mean vaTlu10e,sT ±1 1S,ET. 12, T13, and T14 at 30, 60, and 90 DAI. In addition, soil exchangeable H+ of T1
increased with time. There was no significant difference in soil exchangeable H+ for the
soil with ERP, charcoal, and sago bark ash, irrespective of incubation time.
 
Figure 6. Effects of treatments on soil exchangeable aluminium ions after thirty, sixty, and ninety 
days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate 
 
Agronomy 2021, 11, x  9 of 28 
 
The interaction between the time of incubation and treatment significantly affected 
soil exchangeable acidity (Figure 5). Among the treatments, T1 recorded the highest soil 
exchangeable acidity followed by T2. Soil exchangeable acidity increased as the amount 
of sago bark was reduced from 100% to 75%, 50%, and 25%. Throughout the incubation 
study, the effect of the treatment with charcoal alone at the rate of 100% (T3) on soil ex-
changeable acidity was not significantly different compared to treatment with the combi-
nation of charcoal at 75%, 50%, and 25% and sago bark ash at 25% (T12, T13, and T14). A 
similar trend was also found in soil exchangeable Al3+ (Figure 6). Soil exchangeable Al3+ of 
soil alone (T1) and ERP alone (T2) were significantly higher than those with charcoal and 
sago bark ash. Between T1 and T2, T2 demonstrated significantly lower soil exchangeable 
Al3+. Regardless of the incubation period, soil exchangeable Al3+ for the treatment with 
sago bark ash alone (T4) was not significantly different compared to the treatments with 
charcoal and sago bark ash. 
 
Figure 5. Effects of treatments on soil exchangeable acidity after thirty, sixty, and ninety days of 
incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% 
charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% 
charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: 
Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal 
+ 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock 
phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% 
sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock 
phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 
Agronomy 20221,51%1, 1s8a0g3o bark ash.. Means with different letter(s) within the same incubation period indicate sig- 10 of 28
nificant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
Agronomy 2021, 11, x  10 of 28 
 
+ 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 
100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, 
T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% 
charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: 
Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% char-
coal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt 
rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal 
+ 25% sago bark ash.. Means with different letter(s) within the same incubation period indicate sig-
nificant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
 
The effects of treatments on soil exchangeable H+ are demonstrated in Figure 7. Soil 
FigureFe6xi.gcEuhffraeecn t6sg. oeEfaftbfreelcaett msH oe+nf  tftsoroerna Ttsm1oi elwnextascs ho asnni ggsenoaiiblf lieecxaaclnhutmalnying hieuaimgbhlieoe nars lutahmftaeinrn tihtuhimroty s,ieosi nxostfy  ,aTaftn2ed,r  Tntih3ni,er ttTy4,d ,sa Tiyxs5tyo, f,T ian6nc,du Tb n7ait,ni oTent8,y,w  here
T1: soiTdl a9ly,o snT eo1,f0 Ti,n2 T:cuE1bg1ya, ptTito1rn2o,,c  wkThp1eh3ro, esa pTnh1da: t seToa1ill4o a naleot, n3Te03, ,:T E620g: y,E pagtnyrdpotc 9 kr0op cDhko ApsphIh.o aIstnpe ha+ad1tde0 0ia%tlioocnnhe,a,  rsTcoo3ia:l lE ,egTxy4c:phEta grnoygcpket  arpobhclkoes pHphho+a sotpefh  ate +
100% saTg1o ibnacrkreaasshe, adn wd Tit5h:  Etgimypet.r oTchkeprheo wspahsa tne o+ 1s0ig0%nicfhicaarcnota ld+if1f0e0r%enscageo inba srokials ehx, Tc6h:aEnggyepat rbolcek Hph+ ofsoprh tahtee+ 75%
charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate
 + 25% schoailr cwoailth+ 7E5R%Ps, acghoabracrokaals, ha,nTd9 :sEaggyop tbraorckk apshho,s pirhraetesp+e7c5t%ivech oafr cionaclu+b5a0t%iosna gtiombaer. k ash, T10: Egypt rock
2+
phosphate +A50m%ocnhga rcthoael +tre50a%tmsaegnotsb,a rTk1a shha,dT 1t1h:eE ghyipgthreosctk spohiol sepxhacthea+n2g5e%abclhea rFcoeal +at5 03%0,s a6g0o, baanrdk a9s0h , T12:
Egypt DrocAkIp (hFoisgpuhraete 8+)7. 5U%pcohnar caopalp+li2c5a%tiosang oofb acrhkaarscho, Tal1 3a:nEdgy spatgrooc kbpahrkos pahshat,e s+o5i0l %excchharacnoagle+ab25le% Fsaeg2+o bark
ash, anrdedTu14c:edEg. yTphterroeck wpahso snpoh astiegn+i2fi5c%ancht adricfofaelr+en2c5e% insa sgoibl aerxkcahsahn..gMeaebanles Fweit2h+ bdeiftfwerenetnl eTtt2e ra(ns)dw Tit3h,i n the
same inircruebsaptieonctpiverei oodf iinndcicuabteastigonnifi tciamnted. ifferences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e.,
a > b > c. Bars represent the mean values ± SE.
 
FigureF7i.gEuffreec t7s. oEf ftfreeacttms eonf ttsroenatsmoiel nextsc hoan gseoaibl leexhcyhdarnogeenabiolen shayftderrotghiernty ,iosinxsty ,aaftnedr ntihniertty,d saiyxstyof, ianncudb natiinoent,yw here
T1: soidl aalyosn eo,f Tin2:cuEbgyaptitorno,c wk hpehroes pTh1a: tseoaillo anleo,nTe3, :TE2g: yEpgtyrpotc kropchko psphhoastpeh+a1te0 0a%locnhea, rTco3a: lE, gTy4:pEt groycpkt  rpohckospphhoastpeh ate +
100% sa+g 1o0b0a%rk cahsahr,caonadl,T T5:4E: gEygpytprto crkocpkh opshpohsapteh+at1e0 0+% 10ch0a%rc osaagl +o 1b0a0r%k saasgho, baanrdk aTs5h:, ETg6:yEpgty rpotcrko cpkhpohsopshpahtaet e++ 75%
charcoa1l0+0%75 c%hasarcgooabla +r k10a0sh%,  Ts7a:gEog byaprtkr oacskh,p Th6o:s pEhgaytpet+ r5o0c%k pchhaorscpohala+te7 +5 %75s%ag cohbaarrckoaasl h+, 7T58%: E sgaygpot rboacrkkp ahsohs,p hate
+ 25% Tch7a: rEcogaylp+t 7r5o%cks apghoobsparhkaates h+, T590:%E gcyhpatrcrooackl +p h7o5s%ph saatego+ b75a%rk cahsahrc, oTa8l :+ E5g0y%pts argoockb aprkhoassphh, Tat1e0 :+E 2g5y%pt rock
phosphcahtear+co50a%l +c h7a5r%co asla+go5 0b%arskag aosbha, rTk9a:s Eh,gTy1p1t: rEogcykp tprhocokspphhaostep h+a t7e5+%2 c5h%acrhcaoraclo a+l 5+05%0% sasgagoo bbaarrkk aasshh,, TT1120: :E gypt
rock phEogsypphat treo+ck7 5p%hochsparhcaotael ++ 2550%s cahgaorbcaorakl a+s h5,0T%1 3s:aEggoy bptarrokc aksphh, oTs1p1h:a Eteg+yp50t %rocchka rpchooals+ph2a5%te s+a g2o5%ba crkhaars-h, and
T14: Egcyopatl r+o 5ck0%ph soasgpoh abtaer+k 2a5s%h,c Th1a2rc: oEagl y+p2t5 r%ocskag pohboasrpkhaasthe. +M 7e5a%ns cwhiathrcdoiaffle +re 2n5t%le tstaerg(os) bwairtkh iansthh,e Ts1a3m: eEginycputb ation
periodrioncdkic patheossipgnhiafitcea +n t5d0i%ff ecrhenarcceos able +tw 2e5e%n tsraegaotm beanrtks aacscho, radnindg Tt1o4T:u Ekgeyyp’st HroScDk tpeshtoastpph≤at0e. 0+5 2, 5i.%e., cah>arbco>acl. Bars
represe+n t25th%e msaegaon bvaalruke sas±h.S ME. eans with different letter(s) within the same incubation period indicate sig-
nificant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
 
Agronomy 2021, 11, 1803 11 of 28
Among the treatments, T1 had the highest soil exchangeable Fe2+ at 30, 60, and 90
DAI (Figure 8). Upon application of charcoal and sago bark ash, soil exchangeable Fe2+
Agronomy 2021, 11, x  reduced. There was no significant difference in soil exchangeable Fe2+ be1tw1 oefe 2n8 T2 and T3,
 irrespective of incubation time.
 
FigureF8i.gEufrfee c8ts. Eoffftercetast mofe ntrtesaotnmseoniltse xocnh asnogile aebxlcehfaenrrgoeuasbiloen fsearfrtoeur sth iiorntys, saifxtteyr, athnidrtnyi,n seitxytyd,a yasndof ninincuetbya tdioany,sw here
T1: soiolfa lionnceu,bTa2t:ioEng,y wpthreorcek Tph1:o sspohila ateloanloen, eT, 2T:3 E: Eggyyppt trroocckk pphhoosspphhaatete+ a1lo00n%e, cTh3a:r cEogayl,pTt4 :roEcgky ppthrooscpkhpahtoes p+h ate +
100% s1a0g0o%ba crkhaarscho, aanl,d TT45: :EEggyypptt rroocckkp phohsopshpahteat+e1 +0 01%00c%ha rscaogaol + b1a0r0k% assahg,o abnadrk Ta5s:h ,ETg6y:pEtg yropctkro pckhpohsposhpahtaet e+ + 75%
charco1a0l0+%7 5c%hasracgooabl a+r 1k0a0s%h, sTa7g: oE gbyaprtkr aoschk,p Th6o:s Epghyatpet+ ro5c0k% pchhoarscpohaal t+e 7+5 %75s%a gcohbaarcrkoaals h+ ,7T58%: E sgaygpot broacrkk pahshos, phate
+ 25%Tch7:a rEcgoaylp+t 7ro5%ck spaghoosbpahrkataes h+, 5T09%: E cghyaprtcrooaclk +p h7o5s%p hsaatgeo+ b7a5r%k cahsahr,c oTa8l: +E5g0y%pts arogockb aprhkoassphh, aTt1e0 :+ E2g5y%p t rock
phosphcahtaer+co5a0l% +c 7h5a%rco saalg+o5 0b%arska gaoshb,a rTk9a: sEhg, yTp11t: rEogcykp pt rhoocskpphhaotsep h+a 7te5%+  2c5h%arcchoaarclo +a l5+0%50 %sasgaog obbaarkrk aasshh,, TT1120:: Egypt
rock pEhogsypphta rteoc+k7 5p%hocshpahrcaotael ++ 5205% scahgaorcboarakl a+s 5h0, %T1 3s:aEggoy bpatrrko cakshph, oTs1p1h: aEtegy+p5t0 %rocchka prchooaslp+h2a5t%e +sa 2g5o%b acrhkaars-h, and
T14: Egcoyaplt +ro 5c0k%p hsoasgpoh bataerk+ a25sh%, cTh1a2r:c oEagly+p2t 5r%ocska gpohboasrpkhaasthe. +M 7e5a%ns cwhaitrhcodaiflf e+r e2n5t%le sttaegr(os )bwaritkh ainshth, eTs1a3m: Eeginycputb ation
periodroincdki cpahteossipghnaifitec a+n 5t 0d%iff ecrheanrcceosable +tw 25ee%n straegaotm beanrkts aaschco, radnidng Tt1o4T: uEkgeyyp’st HroScDk tpehstoastppha≤te0 .+0 52,5i%.e. ,caha>rbco>acl . Bars
represe+n 2t5th%e smaegaon bvaarluke ass±h.S ME.eans with different letter(s) within the same incubation period indicate sig-
nificant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean valueFsig ±u SreE.9 demonstrates that the application of charcoal and sago bark ash increased soil
exchangeable K+. Treatment five had significantly higher soil exchangeable K+ compared
Figure 9 demwoith other treaofnthsetrtarteeast mthea
ttm thenet sapwphliicchatwioenre oafm cehnadrecdoawl iathncdh asarcgooa lbaanrdk saasgho ibnacrrkeaasshe.dThe effectsnt with sago bark alone (T4) on soil exchangeable K+ was simila r to those
soil exchangeable K+of T.6 T, rTe7a,tamnednTt 8fiavte3 0haDdA sIiganndifiTc6anattly90 hDigAhIe. rA sto6i0l ex +ancdh9a0ngDeAaIb, lseo iKl e xccohman- geable K+
pared with other dtreecartemaseendtass wthheicraht ewoefrsea gaombeanrdkeadsh wreitdhu ccehdarfcroomal 7a5n%d tsoa5g0o% baanrdk 2a5s%h.. TThhee treatment
effects of the treatwmitehncth warictoha lsagloon eba(Tr3k) aslhoonwee (dTa4)lo own csoonitlr iebxucthioangtoewabarlde sKs+o iwl eaxsc hsiamngileaarb lteo K+.
those of T6, T7, and T8E xacth 3a0n gDeAabIl eanCda2 T+ 6in actr e9a0s eDdAwIh. eAnt c6h0a racnodal 9a0n dDsAagI,o sboailr kexacshawnegreaabplpe lied to the
K+ decreased as thseo rila(tFei oguf rseag10o) .bTarreka tamshe nrtedonuecehdad frtohme l o7w5%es ttoso 5i0l %ex cahnadn g2e5a%bl.e TChae2 t+r.eTahtme eefnfetc t of T2 on
with charcoal alonsoei l(Tex3c)h sahnogweaebdle aC lao2w+ w caosnstirgibnuifitciaonnt ltyohwigahrdersc soomilp eaxrecdhawnigtheaTb1lael tKho+.u gh this treatment
had no charcoal and sago bark ash. There was no significant difference in soil exchangeable
Ca2+ of T2 and T3 at 60 and 90 DAI. Among the treatments with the soil amendments, the
soil exchangeable Ca2+ values of T8 and T12 were higher than those of T4, T5, T6, T9, T10,
T11, and T13 at 30 DAI and T13 at 90 DAI. However, at 60 DAI, the effects of the soil with
charcoal and sago bark ash on exchangeable Ca2+ were similar.
 
Figure 9. Effects of treatments on soil exchangeable potassium ions after thirty, sixty, and ninety 
days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate 
+ 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 
100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, 
T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% 
charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: 
Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% char-
coal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt 
rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal 
 
Agronomy 2021, 11, x  11 of 28 
 
 
Figure 8. Effects of treatments on soil exchangeable ferrous ions after thirty, sixty, and ninety days 
of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 
100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 
100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, 
T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% 
charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: 
Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% char-
coal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt 
rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal 
+ 25% sago bark ash. Means with different letter(s) within the same incubation period indicate sig-
nificant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
Figure 9 demonstrates that the application of charcoal and sago bark ash increased 
soil exchangeable K+. Treatment five had significantly higher soil exchangeable K+ com-
pared with other treatments which were amended with charcoal and sago bark ash. The 
effects of the treatment with sago bark alone (T4) on soil exchangeable K+ was similar to 
Agronomy 2021, 11, 1th80o3se of T6, T7, and T8 at 30 DAI and T6 at 90 DAI. At 60 and 90 DAI, soil exchangeable 12 of 28
K+ decreased as the rate of sago bark ash reduced from 75% to 50% and 25%. The treatment 
with charcoal alone (T3) showed a low contribution towards soil exchangeable K+. 
Agronomy 2021, 11, x  12 of 28 
 
+ 25% sago bark ash. Means with different letter(s) within the same incubation period indicate sig-
nificant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Ba rs 
Figure 9. EffFreiecgptusrreoesf et9nr.et  Eathtfmfee cemtnset saonof  ntvraseolauitlmeese x±nc hStsEa no. gne saobille epxocthaasnsiguemabiloen psoatfatesrsituhmir tyio, nsisx tayf,tearn dthniritnye,t ysixdtayy, saonfdi nnciunbeatyti on, where
T1: soil alondea,yTs2 o: fE ignycupbt aroticokn,p whohsepreh aTt1e: asoloiln ael,oTn3e:, ETg2:y Epgt yropct kropchko pshpohsapteha+te1 0a0lo%nec,h Ta3r:c oEagly,pTt4 r:oEcgky pphtorsopchkapte Exchan hosphate +
100% sago b+a r1k0a0s%h ,cahnadrcTo
gaeab5:l,E Tg4l:e E Ca
2+ i
yptgryopckt r
n reased wh n 
pohcoks pphhaotsep+ha1t0e0 +% 1
c0h0a%rc soaagl and s go bark ash wercharcoal o+ b1a0r0k% assahg, oanbdar kT5a:s Ehg, Ty6p:t reo ackp plhioesdp htoa tteh +e  
1s0o0i%l ( cFhigarucroea l1 +0 )1.0 T0%re asatmgoe bnatr ko naesh h, aTd6:  tEhgey plot wroecskt  pshooils pexhcahtea +n 7g5e%ab clhea Crca2+. T Egypt rock phooal + 7h5e% e fsfaegcot boafr Tk 2a ssophhn,  ate + 75%
charcoal + 7T5s7%o:i lEs eaggxyocphbt aarnrokgckea asphbh,loeTs 7Cp:haEa2g+t eyw p+at s5r 0os%cigk ncphihfaiocrscaponahtlal yt+e  h7+i5g%5h0 e%sra gcchoa mbrcaporakar lae+sdh7 ,w5 %Ti8ths: a ETggo1y bapaltt rhrkocauksgh ph, hT to8hs:ipEsh gtarytepea tt+rm o2ce5k%ntp  hosphate
+ 25% charccohhaaaldr+c no7ao5l  %c+h 7sa5ar%gcoo sabalag arokn bdaas rshka, gaTso9h :b, aETrg9k:y  Epagtsyhrop. ctT krhopechrkeo p swhpohasasp tnehoa+ tse7i 5g+% n7i5fc%ihc aacrnhcato radcliof+afel5 r+0e %5n0c%sea  gisnao gsbooa ibrlka eraxksc ahhs,ahTn, 1gT0e1:a0E:- gypt rock
phosphate +Eb5gl0ey% pCtc ahr2oa+cr ockof p aThl 2+o sa5pn0h%da tsTea 3+g  oa5t0b %6ar0 kc ahanasrdhc, o9Ta01l  1D+: 5AE0gI%y. pA stamrgoooc knbgapr htkoh aseps hthr,a eTtae1t+1m: 2Ee5ng%ytspc htw ariortcchok at plh+heo 5ss0op%ihl asatameg o+e nb25ad%rmk caehsnhatr,s-T, 12: Egypt
rock phosphctaohtaeel  +s o75i50l% e xscachhgaorac nbogarleka+ ab2sl5he% , CTs1aa22g+:  oEvgbayalurpket srao sochfk,  TTp18h3 oa:snEpdghy aTpte1t 2+ro  7wc5k%epr echh ohasirpgchohaetlre + t+ 2h5a%0n%  stahcghooas rbec aoorakfl  Ta+s4h2, 5,T %T51,s3 aT: gE6og, ybTpa9rt, k ash, and
T14: Egypt rroToc1ckk0 p,p Thho1os1spp, hahanattdee + T+ 215530% a tc 3h0ar rcDcoAaallI  +a 2n5d% T s1a3g oa tb 9ar0k D asAhI., .aM Hnedoa wnTs1e4wv: eiEtrhg,y daptift f6 re0or ecDnk tAplheI,to ttsehpre(hs a)etfwef ei+tc h2tis5n %otfh c ethhsaear cmsooeailil n cubation
period indicwateithsi gcnhiafirccaonatld aifnfedr esnacgeos bbaetrwk eaesnht orena temxecnhtasnagcecaorbdlein Cgato2+ Twuekreey ’ssimHiSlDart. est at p ≤ 0.05, i.e., a > b > c. Bars
represent the mean values ± SE.
 
 
Figure 10. EfFfiegcutsreo f1t0r.e Eaftfmecetns tosfo tnresaotmil eexnctsh aonng seoailb elexcchaalcniugemabiolen csaalfctieurmth iiorntys, asfitxetry ,thanirdtyn, isnixettyy, danayds noinf eintycu dbaaytsio n, where
T1: soil alonoef, Tin2c:uEbgaytipotnr,o wckheprheo Tsp1:h saoteil aalloonnee,, TT32:: EEggyypptt rroocckkp phhoosspphhaattee+ al1o0n0e%, Tc3h:a Ercgoyapl,t Tr4o:ckE gpyhpotsprohcaktep +h osphate +
100% sago ba1r0k0%as hc,haanrdcoTa5l,: TE4g:y Epgt yropctk ropchko spphhoastpeh+a1te0 0+% 10ch0%ar csoaaglo+ b1a0r0k% assahg, oanbdar kT5a:s hE,gTy6p:t Ergoyckp tprhoockspphhaotsep +h ate + 75%
100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, 
charcoal + 75T%7: sEaggyopbt arrokckas phh, Tos7p: hEagtyep +t r5o0c%k pchhaorscpohaal t+e +755%0 %sacghoa rbcaorakl a+s7h5, %T8s:a Eggoybpatr kroacskh ,pTh8o:spEhgaytpet +r o2c5k%p hosphate
+ 25% charcochalar+co7a5l% + s7a5g%o sbaagrok baasrhk, aTs9h: , ETg9y: pEtgryopctk ropchko spphhoastpeh+ate7 5+% 75c%ha crhcoaarclo+al5 +0 %50s%a gsoagboa rbkaraks ha,shT,1 T0:10E: gypt rock
phosphate +E5g0%ypct hraorccko aplh+os5p0h%astea g+o 5b0a%rk chasahrc, oTa1l1 +:  E5g0y%p tsargocok bpahrko sapshha, tTe1+1:2 E5%gycphta rroccoka lp+ho50sp%hsaatge o+ b2a5r%k acshha,rT- 12: Egypt
rock phosphcaoteal+ +7 550% cshaagroc obaalrk+ a2s5h%, Ts1a2g:o Ebgayrpkt arsohc,kT p1h3o: sEpghyaptte r+o 7c5k%p hchosaprchoaatle ++ 2550%% sachgaor bcoarakl  +as2h5,% T1s3a:g Eogbyaprtk ash, and
T14: Egypt rorocckkp phhoospsphhaatete+ +2 550%%c chhaarrccooaall+ +2 255%s saaggoob baarrkka asshh., Maneda nTs1w4: iEthgydpiftf erroecnkt plehtotesrp(hs)awtei +th 2in5%th cehsaarmcoeailn cubation
period indic+a t2e5s%ig snaifigoca bnatrdk iaffsehr.e Mnceasnbse wtwitehe nditfrfearetmnte lnetstearc(sc)o wrdiitnhgint othTeu skaemye’s iHncSuDbatteisotna pt epr≤iod0 .i0n5d, iic.ea.t,ea s>igb- > c. Bars
represent thenmifiecaanntv dailfufeerse±ncSeEs .between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
Soil exchangeable Mg2+ of the treatments with ERP and soil amendments (T2, T3,
Soil exchaTn4g, eTa5b,leT 6M, gT27+ ,oTf 8th, eT 9tr,eTa1tm0,eTn1ts1 ,wTi1th2 ,ETR1P3 ,anandd soTi1l 4a)mwenerdemimenptsr o(Tve2d, Tc3o, mT4p,a red with the
T5, T6, T7, T8,t rTe9a,t mT1e0n,t Tw11it,h To1u2t, ETR1P3, aanndd sTo1il4a) mwenred mimepnrtosv(Ted1) c(oFmigpuarere1d1 )w. iAtht 3th0eD tAreIa,tt-he effect of T2
ment without oEnRsPo ialnedx cshoailn agmeaebnledmMegn2t+s w(Ta1s)s (iFmigiluaret o11th).o Aset o3f0 TD1A3 Ia, ntdheT e1f4f.ecTth oefr eTw2 aosn no significant
soil exchangeadbilfefe Mregn2c+e winass osiiml eixlacrh taon tgheoasbel eofM Tg123+ abnedtw Te1e4n. Th2earen dwTas3 naot  6s0igannidfic9a0nDt dAifI-. Additionally,
ference in soil exchangeable Mg2+ between T2 and T3 at 60 and 90 DAI. Additionally, at 
60 and 90 DAI, soil exchangeable Mg2+ contents increased significantly following the in-
troduction of sago bark ash alone (T4) or combined application with charcoal (T5, T6, T7, 
T8, T9, T10, T11, T12, T13, and T14) compared with the treatment with charcoal alone (T3). 
 
Agronomy 2021, 11, 1803 13 of 28
Agronomy 2021, 11, x  at 60 and 90 DAI, soil exchangeable Mg2+ contents increased significantl1y3 ofof l2l8o wing the
 introduction of sago bark ash alone (T4) or combined application with charcoal (T5, T6, T7,
T8, T9, T10, T11, T12, T13, and T14) compared with the treatment with charcoal alone (T3).
 
Figure F11ig. uErfefe c1t1s. oEfftfreecattsm oefn ttrseoantmsoeniltesx ocnha snogiel aebxlcehmanagneaesbiluem miaognns easftieurmth iiortnys,  saifxtteyr, athnidrtnyi,n seitxytyd,a aynsdo fniinnceutbya tion,
where Td1a: ysos iol af lionnceu, bTa2t:iEogny, pwt hroecrke pTh1o:s spohial taelaolnoen,e T, T23: :EEggyyptt rock pphhoospsphhataete+ a10lo0n%ec, hTa3r:c oEagl,yTp4t: rEogcykp pt hroocskpphhaotsep hate
+ 100%+s a1g0o0b%a rckhasrhc,oaanl,d TT45:: EEgypt rocckkp phhoospsphahtaete+ +10 100%0%ch asracgooa lb+ar1k0 0a%shs,a ganodb aTrk5:a Eshg,yTp6t: rEogcykp pt rhoocskpphhaotsep +h ate +
75% cha1r0c0o%al  +ch7a5r%cosagl o+ b1a0r0k%as sha,gTo7: bEagrykp at srohc, kTp6h: oEsgpyhpate r+oc5k0 %phchoasrpchoalte+ +7 57%5%sa gchoabracrokaals +h ,7T58%: E sgaygpot rboacrkkp ahsohs,p hate
+ 25% cTh7a:r cEogayl p+t7 r5o%cks apghoobsaprhkaatseh +,  T590:%E gcyhpatrrcocakl p+h 7o5s%ph astaeg+o 7b5a%rkc haasrhc,o Tal8+: E5g0%ypsta rgoocbka prkhoashp,hTa1t0e: +E g2y5p%t rock
phosphcahtea+rc5o0a%l +ch 7a5rc%o asla+g5o0 b%asrakg aosbha,r kT9a:s hE,gTy1p1:t Ergoycpkt prohcoksphoastpeh +a t7e5+%2 5c%hacrhcaoracol a+l +505%0% sasaggoo bark asshh, ,T T121:0E: gypt
rock phEogspyhpatt ero+ck75 p%hcohsaprhcoaatle+ +2 550%%s acghoarbcaorkala +sh 5,0T%13 s: aEggoy pbtarrokc kasphh,o Tsp1h1a: tEeg+y5p0t% rocchka rpcohaols+p2h5a%tes +a g2o5%ba rckhasrh-, and
T14: Egcyopatlr +o c5k0p%h osaspghoa btear+k2 a5s%h,c hTa1r2c:o Ealg+yp25t %roscakg pohboasrkphasahte.  M+ e7a5n%s wchitahrcdoifafle r+e 2n5t %let tsearg(so) bwairthki nasth,e Tsa1m3:e Eignycupbt ation
period rinodckic aptheossigpnhifiatcea n+t 5d0i%ffe crehnacrecsobael t+w 2e5e%n t sreaagtom beanrtsk aacscho,r danindg Tto14T:u Ekgey’pstH rSoDckt epsht oast ph≤at0e. 0+5 ,2i5.e%., ach>abrc>oacl. Bars
represe+n t2t5h%e m saegano vbaalruke sa±shS. EM. eans with different letter(s) within the same incubation period indicate sig-
nificant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean valuTehsr ±o uSEgh. out the incubation study, T1 showed the lowest soil exchangeable Na+ com-
pared with other treatments (Figure 12). The effects of T2 and T3 on soil exchangeable Na+
Throughoutw theree isnimcuilbaartbiount  ssitgundifiyc,a Tn1tl yshloowweerdth tahnet lhoowseeosft Tso4,ilT e5x, cTh6a, Tn7g,eTa8b,lTe9 N, Ta1+0 c,oTm11-, T12, T13,
+
pared with other atnredaTtm14e.nTthse (rFeigwuarsen 1o2s)i.g Tnhifiec eafnftecdtisff oerfe Tn2ce ainnds oTi3l  eoxnc hsaonilg eexacbhleaNngaeafborlet hNeat+r eatments
were similar but wsigitnhi2fi5c%anstalygo lobwarekr atshhan(T t1h2o, sTe1 o3,f aTn4d, TT51,4 T),6r,e Tga7r, dTl8es, sTo9f, Tth1e0r, aTte11o,f Tc1h2a,r cTo1a3l,u sed and
incubation period. Although soil exchangeable Na+ decreased when the rate of sago bark
and T14. There waashs wnoa ssriegdnuifciecdanbty d25if%fe,rwenitchet iimn es,osiol ilex
+
excchhaannggeeaabbllee NNaa+  ifnocrr etahsee dtr. eatments 
with 25% sago bark aTshhe (iTnt1e2r,a cTt1io3n, abnetdw Tee1n4)t,i mreegoafridnlceusbs aotifo tnhaen rdattree aotfm cehnatrscioganli fiucsaendtl yanafdfe cted soil
incubation periodC.E ACl(tFhiogugreh1 s3o).ilA etx3c0hDanAgI,etahbelseo Nil Ca+E dCeocfreTa2saendd wT7hewne rtehesi mraitlear obfu stasgigon bifiacrakn tly lower
ash was reduced cboym 2p5a%re,d wwiitthh tTim5,eT,8 s,oTi9l ,eaxncdhaTn13g.eAabltlheo Nugah+ iTn5crsheaosweedd. the highest soil CEC at 60 DAI,
the effect was not significantly different compared to T1, T2, T3, T4, T8, T9, T10, T11, T12,
and T13. At 90 DAI, soil CEC of T2 was significantly higher than those of T9, T10, T11, T12,
and T13 but significantly lower compared with T3.
 
Figure 12. Effects of treatments on soil exchangeable sodium ions after thirty, sixty, and ninety days 
of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 
100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 
100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, 
T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% 
charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: 
Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% char-
coal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt 
 
Agronomy 2021, 11, x  13 of 28 
 
 
Figure 11. Effects of treatments on soil exchangeable magnesium ions after thirty, sixty, and ninety 
days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate 
+ 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 
100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, 
T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% 
charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: 
Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% char-
coal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt 
rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal 
+ 25% sago bark ash. Means with different letter(s) within the same incubation period indicate sig-
nificant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
Throughout the incubation study, T1 showed the lowest soil exchangeable Na+ com-
pared with other treatments (Figure 12). The effects of T2 and T3 on soil exchangeable Na+ 
were similar but significantly lower than those of T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, 
and T14. There was no significant difference in soil exchangeable Na+ for the treatments 
with 25% sago bark ash (T12, T13, and T14), regardless of the rate of charcoal used and 
Agronomy 2021, 11,i1n8c0u3 bation period. Although soil exchangeable Na+ decreased when the rate of sago bark 14 of 28
ash was reduced by 25%, with time, soil exchangeable Na+ increased. 
Agronomy 2021, 11, x  14 of 28 
 
rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoa l 
Figure 12. E+Ff i2fge5uc%trse s oa1fg2t.or E ebfaaftermckte san sothfs .t.or Mneasetoaminlesen wxtsci htohan nd sgiofeifale berexlenchts oaledntgitueerma(bs)ilo ew nsisothdaifinute mtrht ieho isnratsmy a, efst ieixnrt cytuh, abirnattydi,o nsnii nxpteyetry, iaodndad yi nsdionifceaitnytec d usaibgya-st ion, where
T1: soil alonnoieff ,iicnTac2nu:tb Edagitfyifopenrte, rnwocchekse rpbehe toTws1pe: ehsnoa ittler eaaallotomnneee,, nTTts23 :a: EcEcggoyyrpdptit nrrgoo cctkok  Tppuhhokosespyph’hsaa HtteeS a+Dlo 1tne0es0t,%  aTt3c ph:  aE≤r g0cy.o0pa5tl, , riT.oe4c.,:k aE  p>gh ybop s>tp crh.o aBctkaer ps+ h osphate +
r1e0p0r%es echnat rtchoea ml, eTa4n:  vEaglyupets  r±o ScEk . phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% sago b1a0r0k%a schh,aarncodaTl 5+: 1E0g0y%p tsarogcok bpahrko sapshha, tTe6+: E1g0y0p%t crhoackrc poahlo+sp1h0a0t%e +s a7g5o%b cahrkaracsoha,l T+6 7:5E%g yspagt oro bcakrpkh aosshp, hate + 75%
charcoal + 7T57%: EsTgayghpoet b irnaortckekra apschht,iooTsnp7 :hbEaetgetyw +pe t5er0no%c tk icmphhaero cosopfa hiln a+ct eu7+5b%a5t0 is%oangc oha anbradcro ktar lae+saht7m, 5T%e8n:s tEa sggioygpnbtai frrikoccaakns htpl,hyTo 8as:pffEhegacytteep dt+  rs2oo5c%ikl  phosphate
+ 25% charCccohEaaClrc+ o(Fa7il5g %+u 7rs5ea% g1 o3s)ab.g aAor ktb 3aa0rsk hD ,aATsh9I,,:  TtEh9ge: y Espgotyirlp oCtc ErkoCpck ho opfs hTpo2hs apatnhead+t eT7 +75  %7w5e%crh eca hrscaiomracoilla+alr 5+ b0 5u%0t% ssa isgganogiobfi abcraaknrkat lsayhs ,hloT, wT101e:0r:E  gypt rock
phosphate +cEog5m0y%ppta crhroeacrdkc  owpahliot+hsp5 T0h%5a,t esT a+8g ,5o T0b%9a, r ckahnadsrhc To, Ta1l13 1+. : A5E0lg%tyh psoatugrgoch bk aTpr5hk o sashsphoh,w aTtee1d1+:  tE2h5ge%y hpcithg rahorceckos tap lsh+ooi5sl0 pC%hEastCaeg  +ao t2 b65a%0r k DcahAsahIr,,- T12: Egypt
rock phospthchoaeate le +f f57e05c%t  wscahagasor  ncbooaartlk s+ aigs2hn5,%i fTi1csa2ag:n Eotglbyya pdrtki frafoeschrke, pnTht1 o3c:sopEmhgapytpaet r+er o7d5c k%top  cTh1oas,r pcToh2a,l t Te+ 3+2,5 5T%04% s,a Tcgh8oa,  brTca9ork,a  lTa+1sh02,,5  TT%113s1:a ,Eg Tgo1yb2pa,t r k ash, and
T14: Egyptaroncdk Tph1o3s. pAhta t9e0+ D25A%I,c shoairlc oCaEl +C2 o5f% Ts2a gwo absa rskiganshif..icManeatlnys whiigthhderif ftehraennt tlehtotesre( so) fw Tit9h,i nTt1h0e, sTa1m1e, incubation
period indiTca1t2e, saingni d 
fiTc1a3n tbduitf fseirgennicfeiscabnettlwye leonwtreera ctmomenptsaraecdco wrdiitnhg Tto3.T ukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars
represent the mean values ± SE.
 
Figure 13. EFfifgeucrtes o1f3.t rEefafetmctes notfs torenastmoiel ncatst ioonn seoxicl hcaantigoen ceaxpcahcaintygea fctaeprathciitryty a,fstiexrt yth, iarntyd, nsiixnteyt,y adnady nsionfetiyn cduabyast ion, where
T1: soil aloonfe ,inTc2u:bEagtiyopnt, rwochkerpeh To1sp: shoaitle aalolonnee, ,TT23: :EEggyyppt trroocckk pphhoosspphhaattee a+lo1n0e0,% T3c:h Eargcyopatl ,rTo4ck:  Epghyopstprhoactke p+ hosphate +
100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 
100% sago b1a0r0k%a cshh,aarcnodalT +5 :1E0g0%yp stargoock baprhko aspshh,a Tte6:+ E1g0y0p%t rcohcakrc pohaol s+p1h0a0t%e +s a7g5o%b cahrakracosha,l T+ 67:5E%g ysapgtoro bcakrkp haoshsp, hate + 75%
charcoal + 7T57%: Esgaygpot braorckk apshho, Tsp7h: aEtgey +p t5r0o%c kchpahrocsopahl a+t e75+%5 0s%agcoh abracroka al s+h7, 5T%8: sEaggyopbta rrokcaks hp,hTo8sp: Ehagtyep +t r2o5c%k phosphate
+ 25% charcchoaarlc+oa7l5 +% 7s5a%g osabgaor kbaarskh ,asTh9,: TE9g: yEpgtyrpotc rkocpkh opshpohspathea+te 7+5 7%5%ch cahrcaorcaola+l +5 05%0%s asgaogob abrakrka sahsh, ,T T1100: :E gypt rock
phosphate +Eg5y0%pt crhoacrkc opahlo+sp5h0%ates a+g 5o0b%a rckhaarscho, aTl1 +1 :5E0g%y psatgroo cbkaprkh oassphh, aTt1e1+: E2g5%ypcth raorccko aplh+os5p0%hastea g+o 2b5a%rk chasahr-, T12: Egypt
rock phospchoaatel + 5705%% scahgaor bcoaarkl  +as2h5,% T1s2a:g Eogbyaprtk raoschk, pTh1o3s:pEhgaytpe t+r 7o5c%k  pchaorscpohaalt +e 2+55%0 %sagchoa bracroka la+sh2, 5T%13s:a Eggoybpat rk ash, and
T14: Egyptrrock phosphatte + 5205% cchhaarrccooaall ++ 2255%% ssaaggoo bbaarrkk aasshh, .aMnde aTn1s4w: Eigthypdti frfoercekn pt hleotsteprh(sa)tew +i t2h5i%n  tchheasracmoael incubation
period indi+c a2t5e%s isgangiofi cbaanrtkd aisffhe.r Menecaenssb wetiwthe deniffterreeantmt leentttesr(asc)c woridthining tthoeT suakmeey ’isnHcuSbDattieosnt paterpio≤d 0in.0d5i,cia.ete., saig>- b > c. Bars
represent thneifmicaenant dviaffleureesn±ceSs Eb.etween treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
3.2. Effects of Am3.e2n.dEinffge cEtsgyopf tA Rmoecnkd PinhgosEpghyaptet wRiotchk CPhaorscpohaal taenwdi tShagCoh Baracroka lAasnhd oSna SgoilB TaroktaAl sh on Soil Total
Phosphorus and PMheohsplihchor-PushoasnpdhoMruehs lich-Phosphorus
Irrespective of Itrrreeastpmecetnivt,e sooifl ttroetaatlm Pe nint,csreoailsetodt awl iPthi nincrceraeasesdingw iitnhcuinbcarteioansi npgeriinocdu bation period
(Figure 14). Tre(aFtimguernet 1o4n)e.  Tsrheoawtmede ntthoe nloewsheostw seodil tthoetallo Pw ceostmspoailrteodt awl iPthc othmep tarereadtmweintths the treatments
with ERP, charcoal, and sago bark ash. At 30 DAI, soil total P of the treatment with ERP 
alone (T2) was significantly lower compared with T3, T5, and T12. However, this trend 
was not consistent throughout the incubation study. At 60 DAI, the soil total P of T6, T11, 
and T14 were similar but significantly higher than those of T2, T3, and T12. Towards the 
end of the incubation study (90 DAI), the soil total P values of the treatments were not 
significantly different except for T1. The treatment with charcoal alone (T3) demonstrated 
lower soil total P at 60 and 90 DAI compared with 30 DAI. 
 
Agronomy 2021, 11, 1803 15 of 28
with ERP, charcoal, and sago bark ash. At 30 DAI, soil total P of the treatment with ERP
alone (T2) was significantly lower compared with T3, T5, and T12. However, this trend
was not consistent throughout the incubation study. At 60 DAI, the soil total P of T6, T11,
and T14 were similar but significantly higher than those of T2, T3, and T12. Towards the
end of the incubation study (90 DAI), the soil total P values of the treatments were not
Agronomy 2021, 11, x  
 significantly different except for T1. The treatment with charcoal alone
15( To3f 2)8d emonstrated
lower soil total P at 60 and 90 DAI compared with 30 DAI.
 
Figure 14. EfFfeigctusreo f1t4r.e Eatfmfecetnst osfo tnresaotiml teonttasl opnh osospil htotrauls pahfotesrpthhoirrutys, asifxtetyr ,tahnirdtyn, isnixetty, daanyds noifnientcyu dbaaytiso onf, iwnchue-re T1: soil
alone, T2: Egbyapttiornoc, kwphheoresp Th1a:t esoaillo naleo,nTe3,: TE2g:y Epgtyropct kropchko spphhoastpeh+a1te0 0a%lonche,a rTc3o:a lE,gTy4p: tE rgoycpkt rpohcokspphhoatsep h+a 1te00+%1 00% sago
bark ash, andchTa5r:cEogayl,p Tt4r:o Eckgypphto srpochka tpeh+o1s0p0h%atech +a r1c0o0a%l + sa10g0o% basarkg oasbha,r kanadsh T, T5:6 E: Eggyyppt trorocckk pphhoosspphhaattee ++ 17050%%c harcoal +
75% sago barckhaasrhc,oTal7 :+E 1g0y0p%t rsoacgkop bhaorskp ahsahte, T+65: 0E%gycphat rrcoocakl +ph7o5s%phsaagteo +b a7r5k%a schh,aTrc8o: aElg +y p7t5%ro cskagpoh obsaprhka atesh+, 2T57%: charcoal
Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal 
+ 75% sago b+a r7k5%as sha,gTo9 b: aErgky apsthr, oTc9k: Epghyopspt rhoactke p+h7o5s%phcahtaer +c o7a5l%+ c5h0a%rcosaalg +o 5b0a%rk saasgho, bTa1r0k: aEsghy, pTt10ro: Eckgypphto rsopchka te + 50%
charcoal + 50p%hosasgpohabtaer k+ a5s0h%, T c1h1a:rEcogaylp +t  r5o0c%k  pshagosop bhaartke +as2h5,% T1c1h:a Ercgoyapl t+ r5o0c%k psahgoospbharaktea +sh 2,5T%12 c:hEagrycpoat lr o+c 5k0p%h osphate +
75% charcoalsa+g2o5 b%arska gaoshb,a rTk12a:s hE,gTy1p3t: rEogcykp pthrooscpkhpahteo s+p h7a5%te +ch5a0r%cocahl a+r c2o5a%l  +sa2g5o% bsaargko absahr,k Ta1s3h: ,EagnydpTt 1r4o:cEkg ypt rock
phosphate +p2h5%ospchartceo +a l5+0%25 c%hasracgooalb a+r 2k5a%sh s.aMgoe abnasrkw aitshh,d aifnfedr eTn1t4l:e Ettgeyr(pst) wroictkh ipnhthosepshaamte +in 2c5u%ba ctihoanrcpoearli o+d indicate
significant di2ff5e%re nsacgeso beatrwk eaesnh.t rMeaetamnesn wtsitahc cdoirffdeirnegnto leTtutekre(sy)’ swHitShDint tehset  astamp ≤e i0n.c0u5b, ia.tei.o, na >pebri>odc. inBdaricsarteep sriegsneinft- the mean
values ± SE.icant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
Soil Mehlich-P demonstrated a different trend compared with soil total P (Figure 15).
Soil MehRlicehg-aPrd dlemssoonfsitnrcautebda taio dnifpfereiondt ,tsroenildM ceohmlipcha-rPedo fwTit1hw saosil tthoetalol wP e(Fstigaumreo n1g5)t.h e treatments.
Regardless ofT ihnecuebffaetcitosno fptehreiotdre, astomile Mnteshwliicth-EP RoPf, Tch1a wrcaosa lt,haen dloswaegsot baamrkonagsh th(Te2 t,rTe3a,t-T4, T5, T6, T7,
ments. The effTe8c,tsT o9f, tTh1e0 t,rTe1a1tm, Te1n2ts,  Tw1i3th,  aEnRdPT, c1h4a) rocnoaslo, ialnMde shalgicoh b-Parwk aesreh h(Tig2h, Ter3,a Tt 43,0 TD5,A I, decreased
T6, T7, T8, T9a, tT610,D TA11I,, aTn1d2,r Tec1o3v, earnedd Ta1t49)0 oDnA soI.ilA Mt 3e0hlDicAh-IP, t hweerreew haigshneor saitg 3n0ifi DcaAnIt, dief-ference in soil
creased at 60 DMAeIh, laicnhd- Prebcoevtwereeedn aTt 290a DndAIt.h Ae tt r3e0a DtmAeIn, thsewrei twhaEsR nPo, scihganricfoicaaln, ta dnidffesraegnoceb ark ash. Soil
in soil MehlicMh-ePh bliecthw-Peeonf T2 awnads tshigen tirfiecaatmntelyntlso weitrht hEaRnPt,h cohsaercoofaTl9, aand sTa1g1ob buatrski ganshifi. cantly higher
Soil Mehlich-Pco omf pTa2r ewdaws isthigTn3ifaicta6n0tDlyA loI.wAetr9 t0hDanA It,htohseee offfe cTt9s oafnTd2 ,TT161, bTu12t ,saignndiTfi1c3anotnlys oil Mehlich-P
higher compawreedr ewsiitmh iTla3r abtu 6t0h DigAheI.r Atht a9n0 tDhoAsIe, tohfeT e3f,fTec5t,sa onfd TT27, .T6, T12, and T13 on soil 
Mehlich-P were similar but higher than those of T3, T5, and T7. 
3.3. Effects of Amending Egypt Rock Phosphate with Charcoal and Sago Bark Ash on Soil
Inorganic Phosphorus Fractions
Figure 16 demonstrates that Sol-P increased following the addition of P to the soil.
However, application of ERP alone (T2) had lower Sol-P compared with T5, T6, and T13 at
30 DAI, T4 and T5 at 60 DAI, and T4, T5, T6, T7, T8, and T11 at 90 DAI. Although T3 and
T4 represents charcoal alone and sago bark ash alone, their effects on Sol-P were similar to
those of the soil with both charcoal and sago bark ash, irrespective of incubation time. It
was noticed that, at 90 DAI, the Sol-P fraction was slightly lower than at 60 DAI.
 
Figure 15. Effects of treatments on soil Mehlich-phosphorus after thirty, sixty, and ninety days of 
incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% 
charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% 
charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: 
Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal 
 
Agronomy 2021, 11, x  15 of 28 
 
 
Figure 14. Effects of treatments on soil total phosphorus after thirty, sixty, and ninety days of incu-
bation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% 
charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% 
charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: 
Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal 
+ 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock 
phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% 
sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock 
phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 
25% sago bark ash. Means with different letter(s) within the same incubation period indicate signif-
icant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
Soil Mehlich-P demonstrated a different trend compared with soil total P (Figure 15). 
Regardless of incubation period, soil Mehlich-P of T1 was the lowest among the treat-
ments. The effects of the treatments with ERP, charcoal, and sago bark ash (T2, T3, T4, T5, 
T6, T7, T8, T9, T10, T11, T12, T13, and T14) on soil Mehlich-P were higher at 30 DAI, de-
creased at 60 DAI, and recovered at 90 DAI. At 30 DAI, there was no significant difference 
in soil Mehlich-P between T2 and the treatments with ERP, charcoal, and sago bark ash. 
Soil Mehlich-P of T2 was significantly lower than those of T9 and T11 but significantly 
Agronomy 2021h, i1g1,h1e80r3 compared with T3 at 60 DAI. At 90 DAI, the effects of T2, T6, T12, and T13 on soil 16 of 28
Agronomy 2021, 11, x  
 Mehlich-P were similar but higher than those of T3, T5, and T7. 16 of 28 
+ 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock 
phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% 
sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock 
phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 
25% sago bark ash. Means with different letter(s) within the same incubation period indicate signif-
icant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
3.3. Effects of Amending Egypt Rock Phosphate with Charcoal and Sago Bark Ash on Soil 
Inorganic Phosphorus Fractions 
Figure 16 demonstrates that Sol-P increased following the addition of P to the soil. 
However, application of ERP alone (T2) had lower Sol-P compared with T5, T6, and T13 
at 30 DAI, T4 and T5 at 60 DAI, and T4, T5, T6, T7, T8, and T11 at 90 DAI. Although T 3 
Figure F1a5ing. Eudfr fTe c41t s5r.oe fEptfrrfeeeasctetmsn eotnsft  stcrohenaastrmocioleaMnlt esah loloincnh se-po ahilno Msdp heshoarlguicosh ab-fptaehrroktsh apirshthyo, rasuilxsot yna,feat,ne rtdh tnehiinirret teyyf, fdseaicxyttssyo ,o fanin cSduo bnla-intPioe wnty, e wdrhaeey srsei moTf1- : soil
alone, Tiin2l:caEurgb tyaopt itotrhnooc, kwseph hoeorfse pt Th1aet:  essaoliioll n awel,oiTnt3he:,  EbTgo2y:t phEt grcyohcpakt rprcohocoakslp  phahanotedsp+ sh1aa0g0teo%  abclhoaanrrkec,o  Tasl3,h:T E,4 g:iryErgpeyts prtoerccoktc ikpvhpeoh sopsfp hihanatcteeu ++b 1a100t0io%n s ago
bark ashcth,imanrcdeo.T aI5lt:,  wETg4ay:s pE tngroytcpikct eprdhooc tskhp hapath,t oeas+tp 19h0a0 t%De Ac+h I1a,0r ct0ho%ael  s+Sao1gl0o-0P %b fasrraakgc oatibsohanr,k  awansdahs ,T s56l::i gEhgytylppytt rl orocwkckep rhp othshpoahsnpat haeat+t 6e7 05+ % D1c0Ah0aI%r. c oal +
75% sagcohbaarcrkoTahls he+,  rT1e07s:0uE%gl tys piantg roFo icbgkauprkrhe oa s1sph7h, a dTte6m+: E5o0gn%yspctthr arrotcecoska  tlph+ha7ot5 s%tphhsea gateod b+da i7rtk5io%ans hc o,hTfa 8Er:cREogaPyl  pi+nt 7cro5rce%ka psheaodgso pt hbeatr eAk+ la-2sP5h% f, rTcah7ca:- rcoal
+ 75% sEatgiooynpb.ta  Arkolcauksm hp,hiTno9is:upEmhgay-tbpeto +ru o5nc0kd%p  Pchh ofasoprrch otaahtele +  t7r75e5%at smcahgeaonrc tbo awlrki+t ah5s0 hE%,R TsPa8g : aoElgboyanrpekt  a(rTsohc2,k)T  pw1h0a:osEs pgsyhigpanteri of+ic c2ka5pn%ht olcyshp alhoracwtoeae+lr  50%
charcoalc+om50%pasraegdo  bwarikthas hT,4T 1a1n: dEg Typ1t1r oactk 3p0h oDspAhIa.t eH+o2w5%evchearr,c oaatl 6+05 0D%AsaIg, othbear kefafsehc,tT o12f: TE2gy opnt r oAckl-pPh owspahsa te +
75% chasricgonali+fic2a5%ntslyag hoibgahrkera sthh,aTn1 3t:hEogsyep ot rfo Tck3,p Tho6s,p Th7a,t eT+95, 0T%12ch, aarncoda Tl +1325 a%t s6a0g oDbAarIk. Aasdh,daintidoTn1a4l:lyEg, ythpet r ock
phosphaitnec+re2a5%sec ihna rAcola-lP+ o2f5 %T2sa wgoabsa drkeateshc.teMde aants 9w0i tDh dAifIf,e wrenhtelerett eTr(2s )hwaidth ihnitghheesra mAel-inPc ucboamtiopnapreerdio wd iintdhi cate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean
values ±TS3E, .T5, T6, T7, T8, T9, T10, T11, T12, T13, and T14. 
 
Figure 1F6i.gEuffreec t1s6o. fEtfrfeeacttms eonft tsroenatlmooesneltys soonl ulobloespelhyo sspohluobrules pafhteorstphhirotyr,ussi xatfyt,earn tdhinritnye,t syixdtayy,s aonfdin nciunbeattyio dna, wysh oerfe T1:
soil alonien,cTu2b:aEtgioynp,t wrohckerpeh To1sp: hsoatiel aalloonnee,, TT32:: EEggyyppt tr orcokckp hpohsopshpahtea+te1 a0l0o%nec,h Tar3c:o Eagl,yTp4t: Erogcykp tprhoockspphhaotsep +h a1t0e0+%1 00%
sago barckhaarscho, aaln, dTT45: :EEggyypptt rroocckk pphhoosspphhaatete+ +1 0100%0%ch saargcooa bl a+r1k0 0a%shs, aagnodb aTr5k: aEsghy, pTt6 :roEcgky ppthroocskphpahtoes p+h 1a0te0%+  75%
charcoalch+a7r5c%oasla +g o1b0a0r%k assahg,oT b7:aErkg yapsthr,o Tck6:p Ehgoyspht artoec+k 5p0h%ocshpahractoea l++ 7755%% cshaagrocboaarlk +a 7sh5,%T 8s:aEggoy bpatrrko caksphh, oTs7p: hate
+ 25% chEagrycopat lr+oc7k5 %phsoasgpohbaatrek +a 5s0h%, T c9h: aErgcyopalt +ro 7c5k%p hsaogspoh baaterk+ a7s5h%, Tc8h:a Ercgoyapl t+ ro50c%k pshagoospbhaarktea +s h2,5T%1 0c:hEargcyopatlr ock
phospha+t e7+5%50 s%agchoa brcaorakl a+s5h0,% T9sa: gEogbyaprtk raoschk,  Tp1h1o: sEpghypatter o+c k75p%ho cshpahracteoa+l 2+5 %50c%h asracgoaol b+a5r0k% assahg, oTb1a0r:k Eagsyhp, Tt 1r2o:cEkg ypt
rock phopshpohsapteh+at7e5 %+ 5c0h%ar ccohaal r+c2o5a%l +s a5g0o%b asrakgaos hb,aTr1k3 :aEshgy, pTt1r1o:c Ekgpyhpots prhoactke +ph5o0%spchhaatrec o+a l2+5%25 %chsaargcoabla r+k 5a0s%h, and
T14: Egyspatgroo cbkaprkh oassph,a tTe1+2:2 5E%gycphat rrcocakl + p2h5o%spsahgaoteb a+r k7a5s%h . cMheaarncosawl it+h 2d5if%fe rseangtole tbtear(ks) awsihth, iTn1t3h:e Esagmype ti nrcoucbka tion
period ipndhiocsaptehsaitgen i+fi c5a0n%t  dcihffaerceonacel s+b 2e5tw%e esnagtroe abtamrekn atshac, caonrdi nTg14to: ETugkyepyt’ sroHcSkD pthesotsapthpa≤te 0+.0 255, %i.e .c, haa>rcbo>alc .+B ars
represen2t5t%he smageaon bvaarlku eassh±. SMEe. ans with different letter(s) within the same incubation period indicate signif-
icant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean valTuehse ±r eSsEu. lt in Figure 17 demonstrates that the addition of ERP increased the Al-P
fraction. Aluminium-bound P for the treatment with ERP alone (T2) was significantly
 
Agronomy 2021, 11, 1803 17 of 28
lower compared with T4 and T11 at 30 DAI. However, at 60 DAI, the effect of T2 on Al-P
Agronomy 2021, 11, x  
 was significantly higher than those of T3, T6, T7, T9, T12, and T13 at 60 DAI. A
1d7d oift i2o8n ally,
the increase in Al-P of T2 was detected at 90 DAI, where T2 had higher Al-P compared
with T3, T5, T6, T7, T8, T9, T10, T11, T12, T13, and T14.
 
FigFuirgeu17r.eE 1ff7e.c Etsfofef ctrtesa otmf ternetsatomn aelnutms ionniu aml-ubmouindiupmho-sbpohuornuds  apfhteor sthpihrtoy,rsuixst ya,fatenrd tnhiniretty,d saixystyo,f ai ncdu bnaitnioent,yw dhaeyres 
T1:osfo iilnaclounbea, tTio2:nE, gwyphterroec kTp1h: ossopihla ateloanloen,e T, T23: :EEggyypptt rorockckp hpohspohsapthe a+t1e0 0a%lonchea,r cTo3a:l ,ETg4:yEpgty rpotcrkoc kphpohospsphhaattee ++ 
1001%0s0a%go cbhaarkrcaosha,la, nTd4T: 5E: gEgyypptt rroocckkp phohsopshpathea+te1 0+0 %10ch0a%rc osaalg+o1 0b0a%rksa agoshb,a raknadsh T, T56: :EEggyyppttr orcokcpkh poshpohsapteh+a7te5% + 
cha1rc0o0a%l + c7h5a%rcsoagaol +b a1r0k0a%sh ,sTa7g:oE bgyaprkt r aosckh,p Tho6s: pEhgaytep+t 5r0o%ckc hpahrcoosapl h+a7t5e% +s 7ag5o%b carhkaarscho,aTl8 +:  E7g5y%p tsraogcko pbhaorskp haasthe, 
+ 25T%7:c Ehagrycopatl r+o7c5k% pshagoospbharaktea s+h ,5T09%: E cghypatrcroocakl p+h o7s5p%ha steag+o7 5b%arckh aarcsoha,l T+85:0 E%gsyapgot broarckka pshh,oTs1p0:hEagtey p+t r2o5c%k  
phocshpahracteo+al5 0+% 7c5h%ar csoaagl o+ 5b0a%rksa agsohb,a Trk9a: sEh,gTy1p1:t Ergoycpkt rpohckospphohsapthea t+e 7+52%5% cchhaarrccooaal l+ +5 05%0%sa gsoabgaor kbaasrhk,  Ta1s2h: E, gTy1p0t: 
rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and
T14E: gEygypptt rroocckk pphhosopshpahtea+te2 5+% 50ch%ar ccohaalr+co25a%l +s a5g0o%ba srkagasoh b. Mareka nasswh,i tTh 1d1if:f eEregnytplett treor(csk)  wpihthoinspthheastaem +e 2in5c%ub cahtiaonr-
percioodali n+d 5ic0a%te ssiaggnoifi bcaanrtkd aifsfher,e Tn1ce2s: bEegtwypeetn rotrcekat mphenotsspahccaotred +in 7g5t%o T cuhkaeryc’soHalS +D 2t5es%t a stapg≤o 0b.a05r,ki .aes.,ha, >Tb13>: cE. gByarpst 
reprroescekn tpthheomspehanatvea l+u e5s0±%S cEh. arcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal 
+ 25% sago bark ash. Means with different letter(s) within the same incubation period indicate sig-
nificant differences betweAenn tarpepartemcieanbtlse aacmcoorudnitnogf toP Twuakseayl’sso HfiSxDed tebsyt aFte p( F≤i g0u.0r5e, 1i.8e).., aR >e gba >rd cl.e Bssarosf the
represent the mean vianlcuuebsa t±i oSnEp. eriod, T1 demonstrated a lower Fe-P fraction compared with the treatments
with ERP. There was no significant difference in Fe-P for T2 and T4, T7, T8, and T14 at
An appreciabl3e0 aDmAoI,uTn8ta ot 6f 0PD wAaI,sa anldsoT 1f1ixaetd90 bDyA FIe. I (rFonig-buoruen 1d8P).f oRretghaertdrelaetsms eonft sthwith charcoaland sago bark ash decreased at 90 DAI. e incu-
bation period, T1 demoRnegsatrrdalteesds  oaf ltorewatemre Fnte,-tPhe frfiaxcattiionno cfoPmaspRaerde-dP waisthn otthceo ntrseisatetmntethnrtosu wghiotuht the
ERP. There was noi nscigubnaitfiiocnanstu diyff(eFrigeunrcee1 i9n). FWei-tPh ftiomr eT, 2T 9a,nTd10 T, a4n, dT7T,1 T1 8in, carenadse Td1t4h eaRt e3d0- PDfAraIc,t ion,
T8 at 60 DAI, and Tw1h1e raeat s9fl0u DctuAaIti.o Inrowna-sbnooutincedd Pfo rfoorth tehretr etraetmatemntes.nAtst 3w0 iDthA Ic,hthaerecfofeaclt aonf Td2 soangRoe d-P
bark ash decreasedf raatc t9io0n DwAasI.similar to T3 and T5 but significantly higher than those of T4, T6, T7, T8, T9,T10, T11, T12, T13, and T14. Reductant soluble P of T2 was significantly higher compared
with T8, T9, and T11 at 60 DAI, and T11 at 90 DAI.
 
Figure 18. Effects of treatments on iron-bound phosphorus after thirty, sixty, and ninety days of 
incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% 
charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% 
charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: 
Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal 
+ 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock 
phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% 
sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock 
phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 
 
Agronomy 2021, 11, x  17 of 28 
 
 
Figure 17. Effects of treatments on aluminium-bound phosphorus after thirty, sixty, and ninety days 
of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 
100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 
100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, 
T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% 
charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: 
Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% char-
coal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt 
rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal 
+ 25% sago bark ash. Means with different letter(s) within the same incubation period indicate sig-
nificant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
An appreciable amount of P was also fixed by Fe (Figure 18). Regardless of the incu-
bation period, T1 demonstrated a lower Fe-P fraction compared with the treatments with 
Agronomy 2021, 11, 1E8R03P. There was no significant difference in Fe-P for T2 and T4, T7, T8, and T14 at 30 DAI, 18 of 28
T8 at 60 DAI, and T11 at 90 DAI. Iron-bound P for the treatments with charcoal and sago 
bark ash decreased at 90 DAI. 
Agronomy 2021, 11, x  18 of 28 
 
 
Figure 18. E2Fff5ieg%cut ssraeog f1ot8 rb.e aEartfkmfe aecsntsht s.o Mof nteraiernaostnm w-beiotnhut snd doifnfpe hirreoonsnpt -hlbeotrtueunrs(dsa )fp twehriottshhpiinhr totyhr,ues sisx aatmyft,eear ni ntdhcuinrbitnyae,t tisoyinxd tpayye, rsaionodfdi  inncidnuiebctaaytt ieod snai,ygwsn ihof-fe re T1: soil
alone, T2: Egiicnyacpnuttb rdaoticfikofenpr,eh wnocshepeshr eba etTet1wa: lesoeonniel  ,tarTleo3an:temE, geTyn2pt:s tE ragocyccpkotrp drhoinocgksp  pthoha oTtesup+khe1ay0t’e0s % aHlocShnDae ,rt cTeos3at:  laE, tTg p4y :p≤Et  0gr.oy0cp5k,t  irp.oeh.c,ok asp >h boat se>p  +hc .a1 tB0ea0+r%s1  00% sago
bark ash, anrdcehpTar5rec:soEeagnly,t  pTtht4er: o Emcgkeyappnht  ovrsaoplcuhkea spt e±h +oSsE1p0. h0a%tec h+a 1r0co0a%l +sa1g0o0 %basrakg aosbha, raknads hT,5T: 6E:gEygpytp rtorcokc kpphhosopsphhataet e++ 17050%% charcoal +
75% sago barckhaarscho,aTl7 +: E10g0y%pt sraogcko pbharoks pahsaht,e T+6:5 E0%gycphta rrococka lp+h7o5s%phsaatgeo +b 7a5rk%a cshha, rTc8o:aEl g+y 7p5t%ro scakgpoh boasprkh aatseh+, T275:% charcoal
+ 75% sago bEagrykpaRt srehog,cakTr 9pd:hlEeogsspsy hpoatft rteor +ec ka5t0pm%he ocnshpta,hr tcahotea lf+ +ix 77a55t%%io csnha ogaorfc  Pboa aarlsk+  Ra5se0hd%, -TPs8 a:w gEoagsyb pnatro krto accsokhn p,shTios1ts0ep:nhEtag ttyeh pr+ot 2ur5og%chk cohpuahtro ctsohpaehl  ate + 50%
+ 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock 
charcoal + 50ipn%hcoussabpgahotaibtoean r+k  s5at0su%hd, yTc h1(1aF:ricEgoguayrl pe+t  15ro90c%).k  Wspahgiotohs p bthaiamrtkee a+, sTh25,9 %T, 1Tc11h: 0aE,r gcaoynapldt + rTo51c0k1%  pisnhacogrsoepbahasaretkde a +ts h2e,5 T%R1 2ec:dhEa-Prgcy ofpratal rc+ot ci5ok0n%p,h  osphate +
75% charcoawsla+hgoe2 r5be%aarssk af lgauoschbt, uaTra1kt2iao: snEh g,wyTpa1ts3  :rnoEocgtkyi cppethdroo sfcopkrh paothteho +sep r7 ht5ar%etea c+thm5ae0rc%notascl.h  +Aa r2tc 5o3%a0l  D+saA2g5oI%,  bthsaarekg e oafbsfehac,r tkT o1af3s h:T ,E2ag noydnp tTR 1reo4dc: k-E gypt rock
phosphate +Pp2 h5for%sapcchthiaoatrnec  o+wa 5la0+s% 2s 5icm%haislracgor aotlo b+ aT r23k5 %asn hsda.  gMTo5e ba banrusktw  asisitghh,n daiifnfifdcea rTenn1t4lty:l e Ehtgtieygrph(ste) rrwo tcihtkha ipnh tohseopsheaam toeef + iT n24c5,u% Tb a6cth,i oaTnr7cp,o eaTrl8 i+o,  d indicate
significant dTif9fe, rTen1c0e,s Tb1e1tw, Tee1n2,t rTea1t3m, eantds  aTcc1o4r.d RinegdtuocTtaunket ys’oslHuSbDle tPes toaf tTp2≤ w0a.0s5 ,si.gen.,iafi>cabn>tlcy. hBiagrshreerp creosmen-t the mean
values ± SEp. ared with T8, T9, and T11 at 60 DAI, and T11 at 90 DAI. 
 
 
Figure 19. EFffiegcutsreo 1f9t.r eEaftfmecetsn otsf otrnearetmduecnttasn otns oreludbulcetapnhto ssopluhobrleu sphafotseprhthoirrutsy ,asfitxetry t,hainrtdy,n siinxettyy, adnady snoinfeitnyc udbaaytsi on, where
T1: soil alonoef, iTn2c:uEbgatyipont ,r owchkeprhe oTs1p:h saotiel aalloonnee,, TT32:: EEggyypptt rroocckk pphhoosspphhaattee +al1o0n0e%, Tc3h: aErcgoyaplt, Tro4c:kE pgyhpostprohcaktep +h osphate +
100% sago b1a0rk0%as hch, aarncdoaTl5, :TE4g: yEpgtyrpotc kropchko psphhoastpeh+at1e0 +0 %10c0h%ar csoaaglo+ b1a0r0k% assha,g aonbda rTk5a: sEhg, yTp6t: Erogcykp tprhoocskpphhaotes p+h ate + 75%
100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, 
charcoal + 7T57%: Esaggyopbt arrokcka sphh,oTs7p:hEagtey p+t 5r0o%ck cphhaorscpoahla t+e 7+5%50 %sagchoa brcaorka la+sh7,5 %T8s: aEggoybpat rrkocaksh p, hTo8s:pEhgaytpe t+r o2c5k%p hosphate
+ 25% charccohaalr+co7a5l %+ 7s5a%go sbaagrok baasrhk, aTs9h:, ETg9:y Epgt yropct kropchko pshpohsapteha+te7 5+% 75c%h acrhcaoraclo+al5 +0 %50%sa gsaogboa brkaraks ahs,hT, 1T01:0E: gypt rock
phosphate +E5g0y%ptc hroacrcko pahl +os5p0h%atsea +g o50b%ar kchaasrhc,oTa1l 1+: 5E0g%yp stargooc kbaprhko aspshh,a Tte1+1: 2E5g%ypcht arorccoka pl +ho5s0p%hastaeg o+ b25a%rk cahshar, -T12: Egypt
rock phosphcaotael ++ 7550% scahgaorc boaarlk+ a2s5h%, Ts1a2g: oEgbyarpkt raoschk,  Tp1h3o:sEpghyaptet +ro 7c5k%p chhoasrpchoaatle ++ 255%0% sacghoa rbcaorakl a+sh25, %T1s3a: gEogybpart k ash, and
T14: Egypt rroocckk pphhoosspphhaattee+ + 2550% charrccoaall + 25% sago bark ash., aMneda nTs14w: iEthgydpiftf reorecnk tplhetotsepr(hsa) twe i+t h2i5n%th cehsaarcmoeali ncubation
period indic+a t2e5%sig snaigfioc abnatrkd iafsfehr.e Mnceeasnbs ewtwithee dniftfreraetnmt elentttsera(csc)o wrditihnign ttoheT uskameye’ sinHcSuDbateiostna ptepri≤od0 .i0n5d,ici.aet.e,  asi>g-b > c. Bars
represent thneimficeaannt vdaiflufeersen±ceSsE b. etween treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
The results further reveal that Ca-P increased with the application of ERP (Figure 20). 
There were no significant differences in Ca-P for the soil with ERP alone (T2) and soil with 
charcoal and sago bark ash at 30, 60, and 90 DAI. 
 
Figure 20. Effects of treatments on calcium-bound phosphorus after thirty, sixty, and ninety days of 
incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% 
 
Agronomy 2021, 11, x  18 of 28 
 
25% sago bark ash. Means with different letter(s) within the same incubation period indicate signif-
icant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
Regardless of treatment, the fixation of P as Red-P was not consistent throughout the 
incubation study (Figure 19). With time, T9, T10, and T11 increased the Red-P fraction, 
whereas fluctuation was noticed for other treatments. At 30 DAI, the effect of T2 on Red-
P fraction was similar to T3 and T5 but significantly higher than those of T4, T6, T7, T8, 
T9, T10, T11, T12, T13, and T14. Reductant soluble P of T2 was significantly higher com-
pared with T8, T9, and T11 at 60 DAI, and T11 at 90 DAI. 
 
Figure 19. Effects of treatments on reductant soluble phosphorus after thirty, sixty, and ninety days 
of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 
100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 
100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, 
T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% 
charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: 
Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% char-
coal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt 
rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal 
+ 25% sago bark ash. Means with different letter(s) within the same incubation period indicate sig-
Agronomyn2i0f2ic1,a1n1,t 1d80if3ferences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bar1s9 of 28
represent the mean values ± SE. 
The results furtherT rheevresaul lths fautr Cthaer-Pre ivnecarl ethaasteCda w-Piitnhc rtehaese adpwpiltihctahteioanpp olifc EatRioPn (oFf iEgRuPr(eF 2ig0u)r.e 20).
There were no signTifhiceraenwt edriefnfeorseingnciefisc ainnt Cdiaff-ePr efnocre sthine Csao-iPl wforitthh eEsRoiPl w ailtohnEeR (PTa2l)o naen(dT 2s)oainl dwsiotihl  with
charcoal and sago bchaarrkc oaaslha nadt s3a0g,o 6b0a,r aknadsh 9a0t  3D0,A60I., and 90 DAI.
 
FigFuirgeu2r0e.  E2f0fe. cEtsffoefcttrsea otmf ternetas tomn ecanlctsiu omn- bcoaulncidupmho-bspohuonruds pafhteorstphhirotyr,usisx tayf,taenrd tnhiinretyty, dsaixytsyo,f ainncdu bnaitnioent,yw dhaeyresT o1f: 
soiilnaclounbea, tTi2o:nE,g wyphterroeck Tp1h: ossopihl aateloanloen, eT, 2T:3 :EEggyypptt rroocckkp phohsopshpahtea+te1 0a0l%onceh,a Trc3o:a lE, gT4y:pEtg ryopctkro pckhophsposhpahtaet e++ 110000% 
sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75%
charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate
+ 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock
 phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt
rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and
T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) within the same incubation
period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars
represent the mean values ± SE.
At 30 DAI, Occl-P of T11 was higher than those of T2, T3, T4, T5, T6, T7, T8, T9, T10,
and T12 (Figure 21). However, the trend changed at 60 DAI, where T3 was significantly
higher compared with T2, T4, T7, T9, T10, T11, T12, T13, and T14. Regardless of treatment,
Occl-P fraction was uniform towards the end of incubation study (90 DAI), with almost all
treatments with ERP making no significant difference.
3.4. Percentages of Soil Inorganic Phosphorus Distribution by Treatment after Thirty, Sixty, and
Ninety Days of Incubation
The initial inorganic P speciation of the soil used in this present study was in the
order of Fe-P (67%) > Occl-P (12%) > Al-P (11%) > Ca-P (7%) > Red-P (3%) > Sol-P
(Table 2). Although the order differed from that recorded in a study carried out by Has-
bullah et al. [78]—Fe-P (68%) > Al-P (13%) > Red-P (10%) > Occl-P (7%) > Ca-P (2%) >
Sol-P—both findings are consistent with that reported by Bidin [79], who mentioned that
Fe-P is dominant in Malaysian soils, with an average of 79%.
Agronomy 2021, 11, x  19 of 28 
 
charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% 
charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: 
Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal 
+ 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock 
phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% 
sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock 
phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 
25% sago bark ash. Means with different letter(s) within the same incubation period indicate signif-
icant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars 
represent the mean values ± SE. 
At 30 DAI, Occl-P of T11 was higher than those of T2, T3, T4, T5, T6, T7, T8, T9, T10, 
and T12 (Figure 21). However, the trend changed at 60 DAI, where T3 was significantly 
higher compared with T2, T4, T7, T9, T10, T11, T12, T13, and T14. Regardless of treatment, 
Agronomy 2021, 11, 1803 20 of 28
Occl-P fraction was uniform towards the end of incubation study (90 DAI), with almost 
all treatments with ERP making no significant difference. 
 
FigFuirgeu2r1e.  E2f1fe.c Etsffoefctrtesa otmf ternetas tomn eoncctlsu doend opchcolsupdheodru ps hafotesrpthoirrtyu,ss iaxftyte, arn tdhinritnye,t ysidxatys, oafnidnc nuibnaetitoyn ,dwahyesr eoTf 1in: scouil-
alobnae,tiTo2n: E, gwyphterroec kTp1h: osophila taeloalnonee, ,TT23: Eggyyppt rto crkocpkh opsphhoastep+ha1t0e0 %alcohnarec,o aTl,3T: 4E: gEygypptt rocckkp phohsopshpathea+te1 0+0% 10sa0g%o  
barckhaasrhc,oaandl, TT54: :E Egygpytprot crkopchko spphaotsep+h1a0t0e% +c h1a0r0co%al s+a1g0o0% bsaargko abasrhk, aasnh,dT 6T:5E:g Eypgtyrpoctk rpohcoks pphhatoes+p7h5a%tec h+a r1c0oa0l%+ 
75%chsaagrocobaarl k+a 1sh0,0T%7: Esagygpot rboacrkkp haosshp,h Tat6e: +E5g0y%pcth raorccoka lp+h7o5%spshagaoteb a+r k7a5s%h, Tch8:aErgcyopatlr o+c 7k5p%ho sspahgaote b+a2r5k% acshha,r cToa7l: 
+ 7E5%gyspagt orobcakrk pahsho,sTp9h: aEtgey +p t5r0o%ck cphhaorscpohaatle ++ 7755%% scahgaroc obaalr+k 5a0s%h,s aTg8o: bEagrykpast hr,oTc1k0 :pEhgoysppthroactke p+h 2o5s%ph cathea+rc5o0a%l 
cha+r c7o5a%l + s5a0g%os abgaorkba arkshas, hT, 9T:1 E1:gEygpypt trroocckk pphhoosspphahtaet+e 2+5 %75c%ha rcchoaalrc+o5a0l% +s 5ag0o%b asrakgaos hb,aTr1k2 :aEsghy,p Tt 1ro0c:k Epghyopspth raoteck+ 
75%phchoasrpcohaalt+e 2+5 %50s%ag ochbaarrkcoasahl ,+T 1530: %Eg yspatgroo cbkaprhko aspshha, teT+115:0 %Egcyhpartc oraolc+k 2p5%hossapgohabtaerk +a s2h5,%an dchTa1r4c: oEagly p+t 5ro0c%k  
phosaspghoa tbea+r2k5 %aschh,a rTco1a2l: +E2g5y%psta groocbkar kphasohs.pMheaatnes w+ i7th5%dif fcehreanrtcloetatel r+(s )2w5i%th isnatgheo sbamareki nacsuhba, tTio1n3p: eErigoydpintd ricoactke  
sigpnihfiocasnpthdaiftfee re+n 5ce0s%be ctwheaerncotraela t+m e2n5t%s a csc± a
ogrdoi nbgatrokT uaksehy,’ saHndSD Tt1es4t:a Et pgy≤p0t. 0r5o, ic.ek. ,pah>obs>phc.aBtaer s+r e2p5r%es ecnht athrecomaela n+ 
values SE.
25% sago bark ash. Means with different letter(s) within the same incubation period indicate signif-
icant differences betweenT threaptemrceenttsa gaecscorfdininogrg taon iTcuPkfeoyll’osw HinSgDt htesat paptl ipc a≤t i0o.n05o,f iE.eR.,P ,ac >h abr c>o acl., Banadrss ago
represent the mean vbaalurkesa s±h SaEr.e summarised in Figures 22 and 23. The proportions of Sol-P and Red-P were
limited compared with other fractions, despite the addition of ERP to the soil. Previous
3.4. Percentages of Sfioinld Iinnogrsg(Faingiucr eP1h6o)ssphhoow
−1
rueds tDhaisttSroibl-uPtriaonng beyd fTrormeat0m.0e5ntot a1.f6te7rm Tghkirgty,. STihxetyd,i satrnibdu tion
Ninety Days of Incuboaf tRieodn- P was only significant in the soil alone (T1), whereas for the other treatments, theamount was negligible because throughout the incubation study, the maximum amount of
The initial inoRregda-nPiwc aPs 0s.p97ecmiagtkiogn−1 o(Ff igthuree s1o9)i.l Iurrseespde citniv tehoifs inpcruebsaetniotn sttimude,yT 1whaasd iFne -tPhwe hich
order of Fe-P (67%w) a>s Omcocrel-tPh a(n1h2a%lf)o >f  thAels-oPi l(i1n1o%rga) n>ic CPafr-aPc t(io7n%s)( r>an Rgiendg-fPro (m3%64)% >t oS8o0l%-P). (ATsaEbRleP was
2). Although the oradpeprlied to the soil, Ca-P became dominant (>74%), replacing Fe-P. Additionally, treatmentswith dERifPf,ecrheadr cforaol,man tdhasatg roecboarrkdaesdh idne ma osntustdrayte cdaarrsiiegdni fiocuatn bt rye dHuactsibonulilnaAh le-Pt and
al. [78]—Fe-P (68%F)e >-P ,Afrlo-mP (8183%%to) a>p Rpreodxi-mPa (te1l0y%13)% > aOt 3c0cDl-AP I(,78%6%) t>o aCpap-rPo x(i2m%at)e l>y S14o%l-Pat—60bDoAthI, and
findings are consist8e1n%t two iatphp trhoxaitm raetpeloyr1te5%d baty9 B0 iDdAinI. [T7h9e],fi wxahtio nmoefnPtinonOecdcl -tPhoaft TF1e-wPa siso dbsoemrv-ed to
inant in Malaysian isnocrielsa,s ewfirtohm a4n% aivne3r0agDeA oI fto 779%%i.n 60 DAI, and 10% in 90 DAI, whereas for the other
The percentagteresa otmf einntos,rtghaendiics tPrib fuotliloonwofinOgcc tl-hPew aapspwliitchaintiothne roafn EgeRoPf,3 c%htaor6c%oa, ilr,r aesnpdec stiavgeoo f the
incubation time and the rates of charcoal and sago bark ash used.
bark ash are summarised in Figures 22 and 23. The proportions of Sol-P and Red-P were 
limited compared with other fractions, despite the addition of ERP to the soil. Previous 
findings (Figure 16) showed that Sol-P ranged from 0.05 to 1.67 mg kg−1. The distribution 
of Red-P was only significant in the soil alone (T1), whereas for the other treatments, the 
 
AgroAnogmroyn o2m02y12, 01211, ,x1 1 , 1803 21 of2 218o  f 28
 
FiFgiugruere2 22.2P. ePrecrecnetnatgaegseosf osfo siloiinl oinrgoargnaicnpich poshpohsoprhuosrudsis dtriisbturitbiountiionnT i1n, TT12,, TT23,, TT43,, TT54,, TT65,, aTn6d, aTn7da fTte7r atfhtierrt yt,hsiirxttyy,, sainxdtyn, iannedty ndinaeytsyo df ainycsu obfa itniocnu,bwathioenre, Tw1h:esroei lTa1lo: nsoei,lT a2l:oEneg,y Tp2t :r oEcgkyppht orospckh ate alone,
phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt 
T3ro: cEkg pyphot srpochkatpeh +o 7s5p%ha cthea+rc1o0a0l% + 7ch5%ar csoaaglo,  Tb4ar: kE gasyhp,t arnodc kTp7:h Eogsypphta treoc+k1 p0h0o%spshagatoe b+a 5r0k%a schh,aTr5co: aElg +y 7p5t%ro scakgpoh boasrpkh aasthe. + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75%
charcoal + 75% sago bark ash, and T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash.
 
Agronomy 2021, 11, 1803 22 of 28
Agronomy 2021, 11, x  22 of 28 
 
 
FiFgiugruer2e3 2.3P. ePrecrecnetnatgaegseso fofs osoilili ninoorgrgaannicicp phhoosspphhoorruussd diissttrriibbuuttiioonn iinn TT88,, TT99,, TT1100,, TT1111,, TT1122,, TT1133,, aanndd TT1144 aaftfeterr ththiritryty, ,ssixixtyty, ,aanndd nninineetyty ddaayys soof finincucubabtaitoino,n w, whehreer eT8T:8 E:gEygpytp rtorcokc pkhpohsopshpahtea te + 25%
ch+a r2c5o%a lc+ha7r5c%oasla +g o75b%ar skaagsoh b, aTr9k: Easghy,p Tt9r:o Eckgypphto rsopchka pteh+os7p5h%atceh +a r7c5o%al c+ha5r0c%oasla +g o50b%ar ksaagsoh b, Tar1k0 :aEshg,y Tp1t0r:o Eckgypphto rsopchka tpeh+os5p0h%atceh +a r5c0o%al c+h5a0rc%oasla +g o50b%ar ksaagsoh ,bTar1k1 :aEshg,y Tp1t 1ro: cEkgypphto rsopchka te + 25%
phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: 
chEagrcyopatl r+oc5k0 %phsoasgpohbaatrek +a 2s5h%, T c1h2a: rEcgoyapl +t  r2o5c%k  psahgoosp bhaartke a+sh75. % charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25%
charcoal + 25% sago bark ash.
 
 
Agronomy 2021, 11, 1803 23 of 28
4. Discussion
4.1. Selected Soil Chemical Properties at Thirty, Sixty, and Ninety Days of Incubation
The sago bark ash alone treatment (T4) had a lower effect on TC because C in the
sago bark volatilised during combustion to produce ash [55]. Carbon is mostly present
in ash in negligible quantities or is even absent. The increase in TC of the soil with
charcoal could be attributed to the relatively high C content in the charcoal. According
Phounglamcheik et al. [80], the C content in charcoal ranges between 84.0 and 92.1%, but
it has a low O, H, and N content. Phonphuak and Thiansem [81] also described charcoal
as an amorphous C in the form of highly porous microcrystalline graphite. The increase
in the soil pH following the incorporation of charcoal and sago bark ash was due to
the basic nature of these amendments (Table 3). However, the charcoal alone treatment
had lower soil pH compared with the treatments with sago bark ash because sago bark
ash has a substantial number of neutralising compounds and base cations. Etiegni and
Campbell [53] indicated that hydroxides of Ca, Mg, and K are the main contributors to
the soluble alkalinity in wood ash. Their reaction with H+ in the soil solution can form
CO2 + H2O and this leads to an increase in pH. The slight increase in the soil pH for T2
suggests that dissolution of Ca and Mg from the applied ERP might have contributed to
the increase in soil pH.
The reductions in soil exchangeable acidity, Al3+, and Fe2+ for the treatments with
charcoal and sago bark ash are related to the increase in soil pH. This finding is consistent
with the findings of previous studies which also reported that decrease in exchangeable
Al3+ and Fe2+ was directly related with the improvement in soil pH [78,82,83]. This was
possible because the hydroxyl ions formed from the dissolution of the CaO, MgO, K2O, and
NaOH in the ash neutralise the protons in the soil solution and those bound on the cation
exchange sites in the soil [84]. The release of the base cations displaced the protons, Al3+,
and Fe2+ occupying the cation exchange site. In addition, the reduction can be associated
with the adsorption of Al and Fe by the charcoal complexion sites. This also suggests that
charcoal is able to reduce Al and Fe solubility by replenishing the functional groups (for
example, carboxylic and phenolic) of humic substances. The increase in soil exchangeable
H+ of T1 at 30, 60, and 90 DAI was due to further hydrolysis of Al3+ resulting in an increase
in the amount of H+. The releasing of H+ was not consistent in this study because there
were no plants to contribute to H+ removal through uptake of nutrients.
The increase in the exchangeable base cations in the soil with the charcoal and sago
bark ash is related to the inherent K, Ca, Mg, and Na contents of these amendments.
Ammonium acetate extraction for the wood ash by Ohno and Erich [85] revealed 48% of
total Mg, 40% of total K, and 5.7% of total P at pH 3.0, whereas Meiwes [86] reported 81%
of total Ca, 57% of total Mg, 34% of total K, and 20% of total P at pH 4.2. Glaser et al. [50]
stated that application of charcoal which has ash adds free bases such as K, Ca, and Mg
to the soil indirectly provide readily accessible nutrients for plant growth. Moreover, the
addition of these base cations to the soil contributes to soil acidity regulation and binding
of exchangeable Al and Fe in the soil [87,88]. Although there was an improvement in the
soil exchangeable cations, the inconsistency in the soil CEC could be associated with the
chemical stability of the charcoal and sago bark ash.
4.2. Total Phosphorus and Mehlich-Phosphorus at Thirty, Sixty, and Ninety Days of Incubation
The increase in soil P availability irrespective of treatment could be attributed to
mineralisation of organic P in soil [89]. Treatment one had the lowest soil total P and
Mehlich-P because there was no addition of mineral P and most of the P ions in the soil
were fixed by Al and Fe ions. The lower soil total P value of the treatment with charcoal
alone at 60 and 90 DAI indicates that without the sago bark ash, the use of charcoal alone
increased soil total P over a short period and the effect lasted for 30 days. The trend of
the soil Mehlich-P was different from the soil total P because not all of the soil total P was
converted into available form. Some of it was held by the soil particles and organic matter
by means of weak outer-sphere mechanisms via anion exchange [90]. The increase in soil
Agronomy 2021, 11, 1803 24 of 28
Mehlich-P at 30 DAI might be because of the readily available P released by ERP. At 60 DAI,
the soil Mehlich-P decreased because some of the added P was fixed by Al and Fe ions.
Recovery of the soil Mehlich-P at 90 DAI suggests that fixed P ions were released into soil
solution either through dissolution or desorption reactions as a result of the increase in soil
pH. This observation corroborates the findings of Demeyer et al. [55] who demonstrated
that P contents in soils are not significantly increased following amendment with wood
ash. Comparative studies of P uptake by corn have shown that ash is substantially less
effective than P fertilisers [91]. These results confirm the conclusions obtained from the
chemical characterisation information on wood ash, because wood ash P is weakly soluble
and a large portion of the dissolved P is likely to be immobilised in the soil [92].
4.3. Soil Inorganic Phosphorus Fractions at Thirty, Sixty, and Ninety Days of Incubation
The P recovery of the P fractions depends on the P added to the soil, suggesting that an
external source of inorganic P is necessary to increase their pool size. The increase in Sol-P
for the treatments with charcoal and sago bark ash compared with soil alone and ERP alone
is partly related to the readily soluble P released by the charcoal and sago bark ash through
mineralisation and dissolution, respectively. However, at 90 DAI, the Sol-P fraction was
slightly lower than at 60 DAI because some of the soil solution P might be converted into
labile P form as a response to maintain equilibrium of P pools in the soil. The decrease in
Al-P and Fe-P following the application of charcoal could be attributed to the production
of organic acids during the decomposition of organic material, which temporarily bind
to the oxides or hydroxides on the surfaces of clay particles. In addition, sago bark ash
as a liming material increases soil pH to reduce the solubility of Al and Fe ions. These
chemical reactions prevent P ions from being precipitated with Al and Fe ions. The increase
in the Ca-P fraction for the treatments with ERP could be associated with the relatively
high concentrations of Ca in this rock phosphate because rock phosphates are generally
made up of calcium apatite, which considerably increase Ca-P fraction in soils [93]. The
distribution of Red-P was not consistent throughout the incubation study, and this is related
to redox reactions involved during the extraction process. The contribution of Occl-P to
plant-available P is limited because it is inert to reactions with the soil solution.
4.4. Percentages of Soil Inorganic Phosphorus Distribution after Incubation
In acidic soils, P sorption is generally attributed to hydrous oxides of Fe and Al and
to (1:1) clays. The dominance of Fe-P fraction of soil alone (T1) is related to lower pH,
higher content of Fe, and the weathering processes of soils. These results corroborated
findings on acidic soils where Fe-P contributed the largest proportion of inorganic P [94].
However, following the application of ERP, Ca-P in soils increased significantly because of
the relatively high Ca in ERP. This result agrees with the studies of Hongqing et al. [93] and
Hasbullah [95], who compared inorganic P speciation of soils with TSP and rock phosphate.
The findings demonstrate that dissolution of water soluble fertiliser (TSP) in acidic soils
produced Al-P and Fe-P, whereas the application of rock phosphate resulted in Ca-P. This
occurs because of incomplete dissolution of rock phosphates. Additionally, the higher
content of Ca-P in soils with ERP suggests that rock phosphate dissolved slowly to ensure
that it supplies P steadily to plants compared with TSP, which dissolves rapidly. The
increase in soil pH explains the low recovery of the Al-P and Fe-P fractions for the soil with
ERP, charcoal, and sago bark ash. Moreover, the reduction in these fractions is believed
to be associated with the precipitation of exchangeable and soluble Al and Fe as well as
insoluble Al and Fe hydroxides on the negatively charged functional groups on charcoal’s
surfaces. The increase in Occl-P for soil alone suggests that without the incorporation of
soil amendments, the occlusion of adsorbed P becomes severe because more adsorbed P is
physically encapsulated by secondary minerals such as Al and Fe oxyhydroxides, which
are essentially inaccessible to plants because they are inert.
Agronomy 2021, 11, 1803 25 of 28
5. Conclusions
Co-application of charcoal and sago bark ash with ERP affects inorganic P speciation
in soils. Calcium-bound P is more pronounced compared with Al-P and Fe-P in soils
with ERP, charcoal, and sago bark ash because these soil amendments are able to increase
soil pH, and at the same time, they reduce exchangeable acidity, exchangeable Al, and
exchangeable Fe. Additionally, amending acidic soils with charcoal and sago bark ash
improves the availability of base cations. Although soil Mehlich-P was not significantly
improved with charcoal and sago bark ash, the fact that these soil amendments were able to
reduce soil acidity indicates that P fixation by Al and Fe could be solved with the continued
use of the amendments to build soil organic matter, which are reputed for improving soil
available P with time. Therefore, the findings of this study suggest that the optimum rates
of charcoal and sago bark ash to minimise P fixation by Al and Fe are 75% sago bark ash
with 75%, 50%, and 25% charcoal. The use of sago bark ash at the rate of 100% is not
recommended because it might increase soil salinity and sodicity. Incorporation of sago
bark ash with charcoal is essential because charcoal has a high affinity for Al and Fe and its
negatively charged surfaces can chelate Al and Fe to free the phosphate ions.
Author Contributions: Conceptualization, P.D.J.; data curation, A.M., L.O. and N.A.H.; formal
analysis, P.D.J.; funding acquisition, O.H.A.; investigation, P.D.J.; methodology, O.H.A., A.M., L.O.
and N.A.H.; project administration, O.H.A.; supervision, O.H.A., L.O. and N.A.H.; visualization,
P.D.J.; writing—original draft, P.D.J.; writing—review and editing, O.H.A., A.M., L.O. and N.A.H.
All authors have read and agreed to the published version of the manuscript.
Funding: This research was funded by Ministry of Higher Education, Malaysia with grant number
[ERGS/1/11/STWN/UPM/02/65].
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The data presented in this study are available within the article.
Acknowledgments: The authors would like to acknowledge Ministry of Higher Education, Malaysia
for financial assistance and Universiti Putra Malaysia for providing research facilities.
Conflicts of Interest: The authors declare no conflict of interest.
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