Communications in Soil Science and Plant Analysis
ISSN: 0010-3624 (Print) 1532-2416 (Online) Journal homepage: https://www.tandfonline.com/loi/lcss20
Reducing Ammonia Volatilization and Improving
Nitrogen use Efficiency of Rice at Different Depths
of Urea Supergranule Application
Kossi Koudjega, Komlan Adigninou Ablede, Innocent Yao Dotse Lawson,
Mark Kofi Abekoe, Emmanuel Owusu-Bennoah & Daniel Kekeli Tsatsu
To cite this article: Kossi Koudjega, Komlan Adigninou Ablede, Innocent Yao Dotse Lawson,
Mark Kofi Abekoe, Emmanuel Owusu-Bennoah & Daniel Kekeli Tsatsu (2019) Reducing
Ammonia Volatilization and Improving Nitrogen use Efficiency of Rice at Different Depths of Urea
Supergranule Application, Communications in Soil Science and Plant Analysis, 50:8, 974-986, DOI:
10.1080/00103624.2019.1594880
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Published online: 12 Apr 2019.
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COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS
2019, VOL. 50, NO. 8, 974–986
https://doi.org/10.1080/00103624.2019.1594880
Reducing Ammonia Volatilization and Improving Nitrogen use
Efficiency of Rice at Different Depths of Urea Supergranule
Application
Kossi Koudjegaa, Komlan Adigninou Abledea, Innocent Yao Dotse Lawsonb,
Mark Kofi Abekoeb, Emmanuel Owusu-Bennoahb, and Daniel Kekeli Tsatsub
aInstitut Togolais de Recherche Agronomique, Lomé, Togo; bDepartment of Soil Science, University of Ghana, Legon,
Accra, Ghana
ABSTRACT ARTICLE HISTORY
An experiment was conducted to determine the depth of urea supergranule Received 24 December 2018
(USG) application that reduces ammonia (NH3) volatilization and improves Accepted 6 March 2019
nitrogen use efficiency of rice. Canne, Voudou, Akuse, and Bumbi series were
used. Treatments involved surface application of prilled urea (PU), USG KEYWORDS
Application depth; ammonia
applied at 0, 4, 8, 12 and 16 cm depths and a control. Rice variety IR-841 volatilization; nitrogen use
was grown up to maturity. Closed chamber device was used to trap NH3. efficiency and USG
Results indicated that the highest mean NH3 loss occurred in Bumbi series
(13.67%) while the lowest was Canne series (8.16%). USG applied at 0 cm
resulted in the highest NH3 loss (37.2%). NH3 volatilization decreased with
increasing depth of USG application. The highest grain yields were obtained
when USG was applied at 4 and 8 cm. In Canne series, the highest agronomic
use efficiency (AE) of N (57 g g−1) was obtained with USG applied either at 8 or
12 cm while the highest recovery efficiency (RE) (84%) occurred at 8 cm. In
Akuse series, the highest AE (55 g g−1) and RE (78%) were obtained when USG
was placed at 8 cm. In Voudou and Bumbi series, the highest AE (45 and 48
g g−1 respectively) and RE (64%) were obtained with USG deep placed at 4 cm.
The results therefore suggested different specific depths of USG application to
reduce ammonia loss and improve nitrogen use efficiency.
Introduction
Nitrogen is one of the most yield-limiting nutrients in rice production around the world (Roy, Misra,
and Montanez 2002), especially in tropical soils where almost every farmer has to apply N fertilizer for
sustainable rice yield (Naher et al. 2011). For rice production, nitrogen fertilizer is an important factor
but low N fertilizer use efficiency remains a problem. Vlek and Stumpe (1978) reported that even
under good fertilization management, nitrogen recovery rarely exceeds 40%. Urea with high nitrogen
concentration of 46% and low unit cost is the dominant N-fertilizer used in crop production (Glibert
et al. 2006). In paddy fields, urea is usually the conventional N fertilizer applied. However, its low
N recovery efficiency remains a problem because of high N potential losses (up to 60% of N applied).
The low recovery is attributed to N losses via diverse pathways such as ammonia (NH3) volatilization,
nitrification, denitrification, leaching and runoff (Fageria and Baligar 1999; Liu et al. 2015).
In general, ammonia volatilization is the most important form of applied urea losses from rice fields
(Chen et al. 2015; Peng et al. 2002). Fan et al. (2006) recorded ammonia losses from 9% to 40% of the
total N applied. Yu et al. (2013) also reported ammonia losses in sandy soil to be 11% to 22%. An
important factor affecting ammonia volatilization is the fertilizer management practice (Preez and
CONTACT Innocent Yao Dotse Lawson innocentlawson@gmail.com Department of Soil Science, University of Ghana,
Legon, Accra, Ghana
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lcss.
© 2019 Taylor & Francis Group, LLC
COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS 975
Burger 2017; Yang et al. 2013). Managing fertilizer practices to reduce ammonia volatilization from soil
is of paramount importance for fertilizer economy and environmental protection because of fertilizer-
based pollution. Rochette et al. (2013b) found that volatilization losses increased exponentially with urea
application rate indicating that as more urea was added to the soil a larger fraction was lost as NH3.
Deep placement of nitrogen was found to significantly reduce total NH3 volatilization by 20–45%
compared with the surface application (Liu et al. 2015).
To reduce N fertilizer losses and increase the efficiency of nitrogen fertilizer use, earlier studies
recommended proper choice of N-sources (Dillon et al. 2012; Jantalia et al. 2012), rates (Dillon et al.
2012; Rochette et al. 2013b; Yu et al. 2013) and timing of application to synchronizeN-fertilizer application
with rice growth stages (Dillon et al. 2012), use of urea inhibitors and coated urea (Cantarella et al. 2008).
Among fertilizer practices that contribute to reduce N fertilizer losses is urea deep placement (UDP). The
deep placement of urea supergranule (USG) is reported to significantly improve urea use efficiency
compared to surface application of prilled urea (Bony et al. 2015; Xiang et al. 2013). Many studies have
established the advantage of USG deep placement over the conventional broadcast practice (Hussain et al.
2015; Qurashi et al. 2013; Xiang et al. 2013). Reduction of N concentration in flood water by USG deep
placement was investigated by Bandaogo et al. (2015) in Burkina Faso.
The effect of depth of USG application on the nitrogen use efficiency has also been investigated by
researchers such as Das et al. (2013) and Kawa et al. (2013). However, there is paucity of information
on how effective USG reduces ammonia volatilization at different depths of application in different
types of soils and that merits research. Therefore, this study was conducted to evaluate ammonia
volatilization rate and to determine the appropriate depth of USG application to reduce urea losses
via ammonia volatilization and to improve N use efficiency of rice in different irrigated paddy soils.
Materials and methods
Soils
The experiment was carried out in pots at University of Ghana, Legon, using soil samples collected
from irrigated rice fields at Kovie and Mission-Tove in Togo; at Kpong and Ashiaman Irrigation
Scheme in Ghana. The soil series, geographic coordinates and major physico-chemical properties are
shown in Table 1.
Plant culture
Plastic pots of 40 cm diameter (at the top) and 30 cm high of 35 L capacity with small holes created at
the bottom were filled with 30 kg of soil leaving a height of 3 cm for flooding. The pots were flooded
for 3 days and puddled. Each pot received four hills of rice variety IR-841 seedling at a planting spacing
Table 1. Some physicochemical properties of the soils used.
Togo Ghana
Kovié Mission-Tove Kpong Ashiaman
Soil Type Canne series (Fluvisol) Voudou series (Fluvisol) Akuse series (Vertisols) Bumbi series (Vertisols)
Geographic coordinates 006° 21ʹ 35 N 006° 21ʹ 30ʹ’N 006° 08ʹ 21ʹ’ N 005° 41ʹ 37ʹ’ N
001° 08ʹ 11ʹ’ E 001° 06ʹ 09ʹ’ E 000° 04ʹ 19ʹ’ E 000° 02ʹ 03ʹ’ W
Sand (%) 11 73 40 64
Silt (%) 16 9 10 9
Clay (%) 73 18 50 27
Texture Clay Sandy-Loam Clay Sandy-Clay-Loam
pH 5.6 5.9 8.1 7.9
OC (%) 1.91 0.72 1.61 1.44
Total N (%) 0.29 0.09 0.25 0.16
Available P (mg/kg) 32.1 13.4 24.1 21.6
CEC (Cmol/kg) 27.5 17.2 31.1 22.2
976 K. KOUDJEGA ET AL.
Rice plant
USG
20 cm 20 cm
Plastic pot
Figure 1. Rice transplanting and USG placement in the pot.
of 20 cm x 20 cm (Figure 1). The rice variety used has maturity cycle of 120 to 130 days and seedlings
were transplanted at 21 days old. Triple Super Phosphate (TSP) and Muriate of Potash (MOP) were
applied as basal fertilizers at recommended rates of 45 kg ha−1 P2O5 and 45 kg ha
−1 K2O (Aboa,
Dantsey-Barry, and Kpomoua 2007).
The treatments imposed consisted of USG application at five different depths: 0, 4, 8, 12, 16 cm
and prilled urea (PU) applied at soil surface (broadcasted in the floodwater ie. 0 cm depth) in three
split applications and a control treatment (without nitrogen application) was included. The treat-
ments were completely randomized with three replications. In the pots receiving USG, one granule
of 1.8 g was deep placed between the 4 hills of rice 10 days after transplanting (DAT). In the pots
receiving PU, urea was equally split into three applications at 10, 45 and 70 DAT in a uniformly
broadcasted mode in the pot at the rate of 1.8 g per pot. The pots were regularly flooded to maintain
2 to 3 cm water layer under the rice plants.
Data collection
Ammonia volatilization
Ammonia volatilized was collected using a modified closed chamber described by Hussain and Malik
(1983) and Wang et al. (2004). The chamber was made of a 25 cm high gray PVC tube. The top of
the tube was tightly sealed with a plastic film to avoid contamination from atmospheric air, and the
bottom of the tube was driven 2 cm deep into the soil. Inside the chamber, a plastic containing 20 ml
of 0.5 M boric acid to absorb the volatilized ammonia was installed on a standing wire support
(Figure 2). The chamber was installed between the four rice hills in each pot immediately after the
first fertilizer application (10 DAT).
Ammonia collection was carried out every 2 days during the first week, every 4 days during the
next two weeks, and every 10 days up to rice maturity. On the sampling days, the boric acid
Plastic film tie
PVC tube
Boric acid solution
NH3 emission
Floodwater
Soil surface
Figure 2. Closed chamber for trapping ammonia.
COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS 977
container was collected and immediately replaced with fresh one. In all, 20 ammonia trappings had
been done over the experimental period from the first urea application to the physiological maturity
stage. In the laboratory, NH3-N content in the boric acid collected was determined by titration with
a 0.01N HCl and the amount of ammonia lost was calculated as follows:.
TC
NH ð%Þ ¼ HCl  0:014  Sp3   100 (1)Sc Nr
where T (mL) is the titre volume of HCl, CHCl is the normality of HCl, 0.014 is milliequivalent of N,
Sc, and Sp (cm2) are the cross-section of the chamber and the surface area of the pot, respectively,
and Nr (g) is the amount of N applied.
Agronomic parameters
Plant height was recorded at the active tillering stage (25 DAT), flowering stage (75 DAT) and at
harvest. Data on the number of tillers, length of panicles, 1000 grain weight, grain and straw yield
were collected at harvest. Rice straw and grain were sampled, oven dried and later analyzed for
N content. Nitrogen use efficiency was evaluated by the agronomic use efficiency of N (AE) and the
N recovery efficiency (RE) calculated as follows:
¼ GYN GYAE 0 (2)
Nr
¼ U%RE N UN0  100 (3)
Nr
where Nr is the rate of N applied (kg pot
−1), GYN and GY0 are the rice grain yield with and without
N application (g pot−1) andU −1N andUN0 are the rice N uptakewithN andwithout N application (g pot ),
respectively. Harvest index (HI) was also calculated as the weight of harvested grain as a percentage of the
total plant weight.
Statistical analysis was run with GenStat software (12th Edition, 2009). Data were subjected to
Analysis of variance at 5% probability level. Means were compared using a protected LSD test (5%).
Results and discussion
Ammonia volatilization rate
In all the four soils, undetectable ammonia volatilization was recorded with the control treatments
(Figure 3). However, ammonia losses were recorded with time with the surface broadcasting of
prilled urea (PU) treatment and the deep placement of urea supergranule (USG) applied at different
depths. Volatilization occurred in all the four soils treated with N within the first 15 days following
each urea application. During this period, 90% to 98% of the total amount of ammonia loss took
place (Figure 4). The peaks of volatilization rates were recorded on the 2nd day after PU application
and at the 4th to 6th day after USG application.
These results corroborate with earlier research findings. Vlek and Stumpe (1978) reported NH3
volatilization occurring during the first few days following N fertilizer application and indicated that
measurements should be done around this period. Ventura and Watanabe (1978) also indicated that
NH3 loss is a quick process which occurs within 9 days following N fertilizer application. Hussain
and Malik (1983) measured ammonia volatilization in flooded rice field and reported that losses
were more during the first five days following N-fertilizer application. Sullivan et al. (2003) evaluated
ammonia volatilization from a swine waste fold amended Bermuda grass pasture and found that
approximately 60% of total NH3 volatilization took place within 4 days after fertilizer application. In
978 K. KOUDJEGA ET AL.
Figure 3. Variation of ammonia volatilization rate per type of soil and nitrogen application mode with time.
Figure 4. Cumulative ammonia volatilization as affected by urea application mode in the different soil types.
the present study, the peaks of ammonia loss rate with USG treatment were delayed 2 to 4 days from
the peak with PU treatment, indicating that ammonia loss was slower with USG than PU application.
This could be due to reduced urease activity and high ammonium retention on soil particles under
urea deep placement.
COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS 979
Ammonia volatilization as affected by the soil type
The different soil types showed significant (p < 0.05) influences on the total ammonia volatilization
(Figure 5). Regardless of the urea application mode, the highest amount of volatilized NH3 (13.67%)
was recorded in Bumbi followed by Akuse series (13.13%). The lowest ammonia loss was recorded in
Canne series soil (8.16%) (Figure 5a).
The differences observed in the amount of volatilized ammonia with regard to the type of soils can be
explained by the variation in their properties (Table 1). The soils from Ghana (Bumbi and Akuse series)
volatilized more ammonia than soils from Togo (Canne and Voudou series) because of the high pH
values. According to Jones et al. (2013), the vulnerability for ammonia volatilization is strongly governed
by the soil pH when urea fertilizer is applied. Ammonia volatilization follows urea hydrolysis that occurs
in alkaline conditions. Longo and DeMelo (2005) found that hydrolysis increased exponentially with pH
while measuring urea hydrolysis in soils under pH ranging from 2.2 to 8.0 under laboratory conditions.
The difference in ammonia loss between soils from the same country could be due to difference in cation
exchange capacity (CEC) and texture. According to Cai (1997), soil CEC plays an important role in NH +4
removal from the soil solution and soils with high CEC reduce N losses as compared to soils with low
CEC. Obcemea, Real, and De Datta (1988) recorded higher ammonia volatilization on sandy soils than
clayey soils.
Ammonia volatilization as affected by urea type and depth of application
Total ammonia loss is significantly (p < 0.05) affected by the mode of urea application (Figure 5b).
Losses ranged from traces for the control (without N application) to 37.2% with the application of
USG at soil surface. Comparing the PU and the USG both applied at the soil surface, USG induced
higher ammonia loss (37.2%) than PU (21%). Within USG deep placement treatments, results
showed that ammonia loss was affected by the depth of application. The deeper the USG was placed,
the lower was ammonia loss. At 4 and 8 cm depths, volatilization amounts were 13.9% and 2.7%
respectively, corresponding to a reduction of about 80%. At 12 cm and 16 cm depths, losses were
0.6% and 0.3%, respectively, corresponding to a reduction of 50%.
The decrease in ammonia loss with the depth of USG application can be explained by the lower
urease activity under urea deep placement compared to the surface application (Liu et al. 2015) and
the fact that deep placement of urea increases fertilizer-soil contact leading to more NH +4 retained
on the soil. As a consequence, there is a reduction of NH +4 concentration in floodwater and
therefore a reduction of ammonia volatilization. The decrease in ammonia volatilization with USG
over PU observed in this experiment is in agreement with Bautista and Koike (2001) and Sommer,
Schjoerring, and Denmead (2004) who reported that point deep placement of urea fertilizer was an
16 50
d
c
14
f
40
12
10 b
a 30
8 e
6 20
d
4
10
2 c
a b ab
0 0
Canne Vodou Akuse Bumbi
Treatment
Type of soil
Figure 5. Cumulative ammonia volatilization as affected by the type of soil and the depth of urea application.
Cumulative NH -N loss 
3
(% N applied)
Cumulative N-NH loss 
3
(% of N applied)
980 K. KOUDJEGA ET AL.
effective application method in reducing ammonia loss. The very low amounts of NH3 emissions
recorded with USG at 12 cm and 16 cm were in accordance with the findings of Rochette et al.
(2013a) who reported negligible NH3 emissions while incorporating urea at depths greater than
7.5 cm.
Application of USG at zero (0) cm resulted in higher ammonia loss as compared with the PU
broadcasted in the flood water. This can be explained by the fact that the broadcasting of PU in
floodwater results in a quick dissolution of urea. This leads to a deep infiltration of a large amount of
dissolved urea into the soil. The hydrolysis of this part of urea occurs in deep soil in reduced
condition and the NH +4 released is readily adsorbed on the soil particles and is therefore prevented
from losses. However, USG dissolves slowly at the soil surface and the released urea undergoes
hydrolysis at the soil surface where oxidation condition prevails, leading to an increase of floodwater
concentration in NH +4 and therefore to a high ammonia loss into the atmosphere (Liu et al. 2015).
Interaction effect of type of soil and mode of urea application on ammonia losses
The interaction between soil and mode of urea application showed significant (p < 0.5) influence on
the total amount of ammonia volatilized (Table 2). When USG was applied at the soil surface, Akuse
series showed the highest amount of NH3-N loss (50% of N applied) followed by Canne series
(44.23%). But when USG was deep placed at 4, 8, 12 and 16 cm, highest ammonia losses were
recorded in Bumbi soil (Table 2). The differences observed in ammonia losses in the different soils
when USG was applied at different depths can be explained by the difference in the characteristics of
the soils. Akuse and Canne series are clayey and may not allow good infiltration of the dissolved urea
in floodwater. Dissolved urea that remains at soil surface increases the concentration of NH +4 in the
floodwater and directly induces very high ammonia volatilization. Bumbi and Voudou series are
sandy loam and might have allowed infiltration of the dissolved urea and restrained ammonium
concentration in the floodwater as explained by Hayashi, Nishimura, and Yagi (2006).
Effect of soil type on rice yield and yield parameters
Soil type significantly (p < 0.05) affected yield parameters and yield of rice (Table 3.). Canne series
showed the highest plant height at maturity (92.8 cm), total number of tillers (23 per pot), length of
panicles (21.7 cm), weight of 1000 grains (27.3 g pot−1), straw and grain yields per pot (78 g pot−1
and 70.6 g pot−1 respectively). The lowest performances were recorded on Bumbi series (Table 3).
Similar total number of tillers, length of panicles and weight of 1000 seeds were recorded on
Voudou, Akuse, and Bumbi series. Canne showed the highest straw yield (78 g pot−1) and grain
yield (70.6 g pot−1) followed by Voudou series (61.3 g pot−1 for straw) and (54.7 g pot−1 for grain).
The lowest straw and grain yields were obtained on Bumbi (48.3 and 43.3 g pot−1, respectively).
Brady and Weil (2008) and Quazi, Datta, and Sarkar (2011) reported significant effects of the type of
Table 2. Interaction effect of soil type and urea application mode on total NH3 loss (% of
N applied).
Type of soil
Urea practice Canne Voudou Akuse Bumbi
Control 0.00 a 0.0 a 0.0 a 0.0 a
PU 9.76 f 21.1 h 24.8 i 33.2 l
USG 0 cm 44.23 m 26.7 j 50.1 n 27.9 k
USG 4 cm 2.86 d 12.9 g 13.7 g 26.1 j
USG 8 cm 0.27 ab 1.4 c 2.6 d 5.2 e
USG 12 cm 0.00 a 0.2 a 0.1 a 2.1 cd
USG 16 cm 0.00 a 0.0 a 0.0 a 1.2 bc
CV 5.6
CV = Coefficient of Variation. Figures with same alphabets are statistically similar.
COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS 981
Table 3. Effect of soil type on rice yield components and yield.
Plant height at Weight of 1000 Straw Grain Harvest
Type of harvest Number of Tillers Length of panicles grains Yield Yield Index
soil (cm) (/Pot) (cm) (g) (g/pot) (g/pot) (%)
Canne 92.8 b 23 c 21.7 c 27.3 b 78.0 d 70.6 d 46 a
Voudou 86.4 a 20 b 20.8 b 26.7 b 61.3 b 54.7 b 47 a
Akuse 92.0 b 21 b 20.8 b 26.7 b 63.9 c 62.6 c 49 b
Bumbi 85.4 a 17 a 17.7 a 24.7 a 48.5 a 43.3 a 47 a
CV 4.5 11.5 4.7 3.9 2.6 3.3 0.9
CV = Coefficient of Variation. Figures with same alphabets are statistically similar.
soil on rice yield components and yield. The effects of soil type on rice yield and yield parameters
can be explained by the differences in the soil properties. These soils were different in texture, pH,
nutrients and organic carbon content. According to Passioura (1991), soil structure alone can
sensitively affect root growth and therefore water and nutrients supply.
Yield components and yield of rice were significantly (p < 0.05) influenced by the mode of urea
application (Table 4). The lowest performances of yield components and yield were recorded with the
control treatment and the USG applied at the soil surface. The control recorded the lowest average plant
height (79 cm) and length of panicles (18 cm) with USG applied at the soil surface (USG 0 cm). The
tallest plant (98 cm) was recorded with the USG applied at 4 cm depth (USG 4 cm). Intermediate height
was shown with the PU treatment, the USG applied at 8, 12 and 16 cm. The highest number of tillers
(26) and length of panicles (21.8 cm) were recorded with the USG deep placement at 4 cm. Similar
number of tillers were recorded with the USG deep placed at 8, 12 and 16 cm (Table 4).
Similar weight of 1000 grains were obtained with USG placed at 4 to 12 cm depth and the prilled
urea applied at the soil surface. The USG applied at the soil surface (control) had the lowest weight
of 1000 grains. The highest grain yield (73.2 g pot−1) and straw yield (80.6 g pot−1) were obtained
with the USG applied at 8 cm depth followed by the USG applied at 4 and 12 cm depths that had
similar yields (Table 4). USG applied at 16 cm gave grain yield lower than 12 cm depth treatment but
similar to the prilled urea (PU). Thus, the grain yield followed the order USG 4 cm >USG 8 cm >
USG 12 cm > PU > USG 16 cm > USG 0 cm> Control.
Significant (p < 0.05) interaction effect of soil type and the mode of urea application on rice growth
parameters and yield was observed (Table 5). On each type of soil, the highest yield varied according to
themode of urea application. In all type of soils, the control showed the lowest yield (18.2 to 34. 8 g pot−1)
followed very closely by the USG applied at the soil surface (30.7 to 41.7 g pot−1). Therefore, it can be
concluded that application of USG at the soil surface is a waste of fertilizer and this mode of application
cannot increase the yield of rice over an unfertilized plot. USG applied both at 4 and 8 cm gave the
highest grain yields in Bumbi and Voudou series, while USG applied at 8 cm gave the highest yield
(81.7 g pot−1) in Akuse series. In Canne series, the highest grain yield was obtained with application of
Table 4. Effect of urea application mode on rice yield components and yield.
Number of Weight of 1000 Grain Straw Harvest
Plant height Tillers Length of panicles grains Yield Yield Index
Treatment (cm) (/pot) (cm) (g) (g/pot) (g/pot) (%)
Control 78.7 a 9 a 18.1 a 25.7 a 34.2 a 30.9 a 46.3 a
PU 84.0 b 24 c 20.6 b 26.8 bc 61.3 d 68.1 c 47.5 c
USG 0 cm 78.6 a 15 b 18.1 a 26.2 ab 42.4 b 48.9 b 46.6 ab
USG 4 cm 98.4 d 26 d 21.5 c 26.6 bc 74.5 f 82.0 e 47.6 c
USG 8 cm 94.8 c 24 c 21.6 bc 26.3 abc 72.7 f 80.1 e 47.6 c
USG 12 cm 95.5 cd 24 c 21.1 bc 26.0 ab 64.3 e 71.3 d 47.3 c
USG 16 cm 94.3 c 24 c 20.9 b 27.6 c 57.7 c 65.3 c 46.7 b
CV 4.5 11.5 4.7 3.9 2.6 3.3 0.9
CV = Coefficient of Variation. Figures with same alphabets are statistically similar.
982 K. KOUDJEGA ET AL.
Table 5. Interaction effect of soil type and mode of urea application on rice yield (g/pot).
Type of soil
Urea practice Canne Voudou Akuse Bumbi
Control 18.2 a 28.1 b 34.8 cd 25.2 b
PU 79.7 qr 73.0 npq 62.2 lm 46.7 fgh
USG 0 cm 38.3 de 40.3 def 41.7 ef 30.7 bc
USG 4 cm 78.8 q 66.7 mn 71.7 np 53.9 jk
USG 8 cm 95.2 t 63.3 lm 81.7 rs 52.4 ijk
USG 12 cm 96.3 t 58.7 kl 74.9 npq 49.1 ghi
USG 16 cm 87.7 s 52.7 ijk 71.6 np 45.4 fg
CV 7
CV = Coefficient of Variation. Figures with same alphabets are statistically similar.
USG both at 8 and 12 cm. Except for Canne series where PU gave similar grain yield as USG 4 cm, deep
application of USG at 4, 8, 12 and 16 cm significantly (p < 0.05) increased yield over PU. OnAkuse series,
USG applied at 4 cm depth increased grain yield by 10 g pot−1 over PU (62.2 g pot−1). Applied at 16 cm
depth, USG showed lower grain yield for all soils (Table 5).
It appeared that the appropriate depths of USG application for better grain yield were 8 to 12 cm
in Canne series, 4 to 8 cm in Voudou and Bumbi series and 8 cm in Akuse series. These results are in
agreement with Das et al. (2014), who worked on silty loam soils and recorded the best yield
parameters and yield of rice with USG applied at 8 cm depth.
Nitrogen use efficiency as affected by the soil type and the mode of urea application
Nitrogen use efficiency (NUE) was significantly (p < 0.05) affected by the soil type (Figure 6).
Regardless of the mode of urea application, the highest agronomic use efficiency (AE) (65 g g−1) and
nitrogen recovery efficiency (RE) (42%) were obtained in Canne series. Bumbi and Voudou series
showed the lowest AE (26 g g−1 on average), while Ashiaman series alone showed the lowest RE
(38%). The differences in the optimum application depth of USG for the best rice nitrogen use
efficiency can be attributed to the differences in the soil properties. Baligar and Bennett (1986) stated
that the physico-chemical properties such as bulk density, structure, texture, water holding capacity
and organic matter content affect plant growth, yield and NUE.
The different modes of urea application significantly (p < 0.05) affected the rice NUE (Figure 7).
The highest AE (47.5 g g−1) was observed when USG was deep placed either at 4 or 8 cm depth,
while the highest RE (70%) was obtained with USG 8 cm treatment. USG applied at the soil surface
showed the lowest AE (9.84 g g−1) and RE (18.6%).
60 80
c
AE RE
70 b
50 c
b
60
40
50 b a
a
a
30 40
30
20
20
10
10
0 0
Canne Voudou Akuse Bumbi Canne Voudou Akuse Bumbi
Type of soil Type of soil
a b
Figure 6. Effect of the type of soil on the agronomic efficiency (a) and Nitrogen recovery (b).
-1
Agronomy use efficiency (g pot )
Nitrogen recovery efficiency (%)
COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS 983
60 80 d e
e
e
AE 70 RE
50 c
d 60
b b
c
40
b 50
30 40
30 a
20 a
20
10
10
0 0
PU USG USG USG USG USG PU USG USG USG USG USG 
0cm 4cm 8cm 12cm 16cm 0cm 4cm 8cm 12cm 16cm
Mode of Urea application
Mode of urea application
a b
Figure 7. Effect of mode of urea application on the Agronomic efficiency (a) and Nitrogen recovery efficiency (b).
The higher AE obtained with the USG deep application over the broadcast PU can be due to the
better N fertilizer-soil contact establishment with USG that increased fertilizer NH +4 retention onto
soil particles and ensures its continuous availability for plant uptake during the growing season as
documented by Savant and Stangel (1990) and Mohanty et al. (1999). De Datta and Creswell (1982)
pointed out that USG, as slow-release N fertilizer, reduces total N concentration in soil surface and is
likely to minimize loss through volatilization and increase NUE. On the contrary, high fertilizer
nitrogen losses under PU application subsequently results in lower rice nitrogen uptake and NUE as
compared with USG.
Nitrogen use efficiency as affected by the interaction between the soil type and the mode of
urea application
Significant (p < 0.05) interaction effect of soil type and the mode of urea application on NUE was
observed (Table 6). The rice NUE in a given soil depended on the mode of urea application. In
Canne series, the highest AE (57 g g−1 on average) was obtained with USG applied at 8 or 12 cm
Table 6. Interaction effect of soil type and mode of urea application on agronomic use
and recovery efficiency.
Type of soil
Treatment Canne Voudou Akuse Bumbi
Agronomic use efficiency(g/g)
Control – – – –
PU 34.4 ef 32.4 de 34.7 ef 28.9 d
USG 0 cm 9.5 a 8.1 a 11.3 ab 10.4 ab
USG 4 cm 51.1 kl 44.6 hi 50.3 jk 48.1 ijk
USG 8 cm 58.4 m 37.9 fg 55.1 lm 34.4 ef
USG 12 cm 55.5 m 23.3 c 46.4 ij 19.7 c
USG 16 cm 44.1 hi 14.0 b 42.1 gh 12.4 ab
Recovery efficiency (%)
Control – – – –
PU 51.9 i 46.1 h 46.8 h 32.4 f
USG 0 cm 25.6 d 13.3 a 15.9 b 19.6 c
USG 4 cm 72.9 n 63.7 l 66.5 m 64.3 lm
USG 8 cm 83.7 p 60.8 k 77.9 o 56.5 j
USG 12 cm 78.9 o 29.3 e 73.4 n 39.8 g
USG 16 cm 76.8 o 20.8 c 63.3 l 15.2 ab
CV 2.7
CV = Coefficient of Variation. Figures with same alphabets are statistically similar.
-1
Agronomy use efficiency (g pot )
Nitrogen recovery efficiency (%)
984 K. KOUDJEGA ET AL.
while the highest RE (84%) was shown by USG 8 cm treatment. In Akuse series, the highest AE
(55 g g−1) and RE (78%) were obtained when USG was placed at 8 cm depth. In Voudou and Bumbi
series, the highest AE (45 and 48 g g−1, respectively) and RE (64%) were obtained with USG deep
placed at 4 cm. In all soils, the lowest AE was obtained with the USG 0 cm treatment. Similar trend
was obtained for the RE in the soils except in Bumbi series which showed lower RE (15%) with USG
16 cm treatment. The PU exhibited higher AE and RE than USG 16 cm in Voudou and Bumbi
series. On the contrary, all USG deep placement treatments showed higher AE and RE than the PU
in Canne and Akuse series.
Conclusion
USG deep placement reduced ammonia volatilization in paddy soils more than the split application
of prilled urea. The greater the depth of USG placement, the lower the amount of ammonia loss.
Ammonia loss was affected by the type of paddy soil. Specific application depths of USG in paddy
soils are required to reduce ammonia loss, enhance rice growth, and increase rice yield, AE and RE.
Results also suggested that, under no circumstance, should USG be applied at the soil surface. The
optimum application depths were 8–12 cm in Canne series (clay, acid and high CEC), 8 cm in Akuse
series (clay, high CEC and alkaline) and 4 cm in both Voudou (sandy-loam, low CEC and slightly
acid) and Bumbi series (sandy-clay-loam, low CEC and alkaline). The study recommends the
application of USG at 6 cm. However, in order to take into consideration local specific environ-
mental conditions, these results need to be confirmed by field investigation.
Acknowledgments
The authors wish to thank the West Africa Agricultural Productivity Program of Togo (WAAPP-Togo) and the
Institute of Agricultural Research of Togo (ITRA) for financing this study.
Notes on contributors
Kossi Koudjega is a PhD candidate of Department of Soil Science, University of Ghana. Researching on nitrogen loss
in rice fields.
Komlan A. Ablede ia a PhD candidate of Department of Soil Science, University of Ghana. Researching on nutrient
management in rice.
Innocent Y. D. Lawson is a senior lecturer in the Department of Soil Science. Area of specialization is Soil
Microbiology and Fertility. Current research on nitrogen leaching in the soil.
Mark K. Abekoe is an Associate Professor in the Department of Soil Science in the area of Soil Chemistry and Fertility.
Emmanuel Owusu-Bennoah is an Associate Professor in the Department of Soil Science in the area of Soil Chemistry
and Fertility.
Daniel K. Tsatsu is a senior technician in the Department of Soil Science who assists in research activities.
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