Department of Soil Science
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Item Phosphorus Nutrient Management In Rainfed Lowland Rice Production In Some Acid Soils Of Togo(University of Ghana, 2018-07) Ablede, K.A.In Togo, rice (Oryza sativa L.) is mainly cultivated on highly weathered acid soils where plant-available phosphorus is generally deficient due to the inherent low P availability of acid soils. Suboptimal and unbalanced P fertilizer rates used by rainfed rice farmers in Togo is often the main cause for low yields. The blanket P fertilizer recommendation applied to the rainfed lowland rice acid soils is outdated and thus, does not take into account the current fertility status of the soils. Moreover, information on P sorption characteristics and standard phosphorus requirements (SPR) of rainfed lowland rice acid soils in Togo is lacking. The present research focused on improving upon P fertilizer recommendations in rainfed lowland rice soils in Togo based on an appropriate SPR for the high P use efficiency by rice. Phosphorus adsorption study was carried out on four rainfed lowland rice growing acid soils of Togo. These soils were collected from Akata Adame, Tchangaide, Kaniamboua and Tchitchao. Phosphorus sorption characteristics and standard P requirements (SPR) of the four soils were evaluated in the laboratory and were related to some chemical properties of the soils. A greenhouse experiment was also conducted using these four lowland soils to determine the response of rice (variety IR 841) to the different phosphorus fertilizer rates and to assess the phosphorus uptake and P use efficiency. Five phosphorus treatments namely, control: 0 mg P kg−1, P recommended rate (RR): 5 mg P kg−1, 4 × RR: 20 mg P kg−1, ½ SPR and SPR where the amounts of P needed to maintain the SPR were applied to the different soils as 62.70, 65.43, 70.40 and 74.85 mg P kg-1 for Kaniamboua, Tchangaide, Tchitchao and Akata Adame, respectively. A researcher-farmer-managed field trials were conducted at two sites (Akata Adame and Kaniamboua) to validate results obtained from the greenhouse study. Five treatments including control (0 kg P ha-1), RR (13 kg P ha-1), 2 × RR (26 kg P ha-1), 4 × RR (52 kg P ha-1) and ½ SPR (92 and 88 kg P ha-1 for Akata Adame and Kaniamboua, respectively) were applied. The study showed that P sorption of the four rainfed lowland paddy soils fitted well into the Langmuir isotherm model and the maximum adsorption followed the order Akata Adame (200 mg kg-1) > Tchitchao (167 mg kg-1) > Tchangaide (154 mg kg-1) > Kaniamboua (143 mg kg-1). The standard phosphorus requirements (SPR) were 62.70, 65.43, 70.40 and 74.85 mg P kg soil for Kaniamboua, Tchangaide, Tchitchao and Akata Adame, respectively. Sorption maximum was positively correlated with the SPR (r = 0.629) and clay fraction (r = 0.712) (P < 0.05), but negatively correlated with soil pH (r = - 0.921), organic carbon (r = - 0.959) and available P (Bray-1) (r = - 0.863) (P < 0.01). From the greenhouse experiment, no significant difference (P > 0.05) between the control treatment and the P recommended rate (RR) and between the ½ SPR and the SPR was observed for the rice shoot dry matter yield. In the field experiment, the maximum rice grain yield was obtained at the two sites with the highest P application rates. At Akata Adame as well as Kaniamboua, the recommended P fertilizer rate (13 kg P ha-1) did not significantly (P > 0.05) increase the rice grain yield as compared to the control (without P application). However, higher P rates showed significant (P < 0.05) increase in grain yields. Phosphorus application at 26, 52 and 92 or 88 kg P ha-1 increased the rice grain yields by 2.5, 3.2 and 3.99 folds, respectively at Akata Adame and by 2.07, 2.83 and 3.45 folds respectively at Kaniamboua, as compared to the control. Significant (P < 0.01) linear relationships with r = 0.992 and 0.995 were observed between rice grain yield and total P uptake at Akata Adame and Kaniamboua, respectively. Farmers from Akata Adame obtained only 1.13 t ha-1 of rice grain when no P fertilizer was applied compared with increases in grain yield when P fertilizer was applied. At ½ SPR, farmers could obtain more than 4 tons per ha (4.26 t ha-1). Compared with the familiar P recommended rate in Togo, farmers could only obtain 1.46 t ha-1 of grain yield. At Kaniamboua, farmers could obtain only 1.33 t ha-1 of grains without P fertilizer application. With ½ SPR, they could obtain up to 4.41 t ha-1 of grain yield which is much higher than that obtained with the P recommended rate (1.61 t ha-1). Economic analysis of the grain yield data obtained from the field experiments showed that with the P fertilizer recommended rate to rice in Togo, a farmer would obtain only 62.60 and 47.10 US$ per ha at Akata Adame and Kaniamboua, respectively. The application of the ½ SPR will enable a rice farmer to realise higher returns of 753.23 US$ per ha at Akata Adame and 749.38 US$ per ha at Kaniamboua. The conclusion from the study is that the P fertilizer rate of ½ SPR may be recommended for rainfed lowland rice production in the study areas of Togo.Item Management of Urea Supergranule (USG) Application to Improve Growth and Yield of Rice (Oryza Sativa L) In Some Paddy Soils of Togo and Ghana(University of Ghana, 2018-07) Koudjega, K.Nitrogen (N) is known to be a major limiting crop nutrient which is required in large amounts as compared with other major nutrients. In rice (Oryza sativa L.) cropping, urea is the main source of N which is applied to the crop because of its relatively low cost and its high N concentration (46%). However, low N use efficiency is always associated with urea application under paddy fields because of its high N loss, mostly through ammonia (NH3) volatilization. The split application of prilled urea (PU) has for a very long time being the common strategy for reducing urea-N losses but its efficiency has been of much concern of late. The present study addresses the increase in rice yield and nitrogen use efficiency (NUE) using the urea supergranules (USG) deep placement. The study comprised of (i) a greenhouse experiment carried out in the Sinna Garden, University of Ghana to evaluate the effect of USG application at different depths on ammonia volatilization, rice yield and NUE in some paddy soils, (ii) a field trial conducted in 2017 in the irrigated scheme of Zio valley in Togo to determine the efficiency of USG and its optimum rate to improve rice yield and NUE in three paddy soils and (iii) an open field pot experiment to determine the effect of seedling age and time of application of USG on rice yield and NUE. The first experiment comprised four paddy soils: Canne and Voudou series that belong to Oxisols (USDA) were sampled in Togo, and Akuse and Bumbi series that belong to Vertisols (USDA) were sampled in Ghana. Six modes of urea application were formulated as treatments: prilled urea (PU, 1.8 g pot-1) applied at soil surface and urea supergranule (USG 1.8 g) applied at soil surface (0 cm) 4, 8, 12 and 16 cm depths and a control without N application. Rice variety IR-841 was planted and a closed chamber device method was used to trap NH3. The results indicated significant decrease in ammonia loss with deep placement of USG over surface split application of PU in the different paddy soils. Regardless of the depth of USG application, the type of paddy soil significantly affected the cumulative ammonia loss which varied from 8% of N applied in Canne series to 14% in Bumbi series. Ammonia loss decreased drastically with depth of USG application (37% of applied N at the soil surface to 0% at 16 cm depth). The USG deep placement significantly increased rice yield and agronomic use efficiency (AE) over PU in the different paddy soils. The optimum depth of USG application to reduce ammonia loss and to achieve the highest yield and AUE varied according to the soil type: 4 cm in Voudou and Bumbi series, 8-12 cm in Canne and 8 cm in Akuse series. The field experiment was conducted at three different sites in Togo (Ablotsri, Hahome and Kouto). Three factors were studied: rice variety (IR-841 and TGR-405), the type of urea (PU and USG) and the N rate (0, 52, 78 and 104 kg ha-1). Results indicated that the efficiency of USG deep placement (UDP) varied significantly with the rice cropping and site. USG significantly increased rice growth parameters and yield over PU. Rice yield increased by 17-23% on the clay soil of Ablotsri and sandy-clay-loam soils of Hahome. In the sandy-loam soil of Kouto, USG increased grain yield only by 4% in the first season while in the second, USG and PU gave similar yields. The TGR-405 rice variety increased grain yield over IR-841 by 5-7% but there was no significant interaction effect between the type of urea and rice variety. The USG increased nitrogen uptake by 34-47 kg ha-1, agronomic use efficiency (AE) by 13-16 kg kg-1 and recovery efficiency (RE) by 13-16 over PU at Ablotsri and Hahome sites while at Kouto site, no significant increment in the parameters was obtained with USG when compared to PU. Rice yield increased with increasing USG rates. However, application of USG rate of 78 kg ha-1 at Ablotsri site, and 104 kg ha-1 at Hahome site were more lucrative, while at Kouto site, 104 kg ha-1of PU gave the highest income. The third experiment consisted of four different ages of seedling (10, 14, 21 and 28-days old) and four different USG application times (0, 7, 14, and 21 days after transplanting (DAT). Results indicated that the younger the seedlings, the better were rice performances. The highest rice yield, NU, AE and RE were obtained with 10 and 14-day old seedlings, while the poorest performances were observed for 28-day old seedlings. Application of USG at 7 or 14 DAT gave the highest rice parameters. The interactions between seedling age and time of USG application showed the highest rice performances when USG was applied at 7 or 14 DAT to rice seedlings of 10 to 14-day old. The overall conclusion from the research was that the USG deep placement significantly reduced ammonia loss in paddy soils over the PU. The optimum depth and rate of USG application to improve rice growth yield and NUE are soil specific. Young seedlings and early USG application (7-14 DAT) should be considered for best rice cropping. .Item Phosphorus Reactions in Three Contrasting Soils Amended with Biochar(University of Ghana, 2018-03) Eduah, J.O.The reactive nature of phosphate leads to the formation of insoluble Fe, Al and Ca bound P compounds in highly weathered tropical soils. Biochar amendments can change the surface chemical properties of highly weathered tropical soils, and hence affect phosphorus retention and distribution in soils. The overall objective of this study was to investigate P reactions with biochar and biochar amended soils of Ghana for effective P management. To achieve this, three major experiments were conducted: (1) phosphorus adsorptive characteristics of different biochar types namely cocoa pod husk, rice husk, corn cob and palm kernel shell biochar produced at two pyrolysis temperatures (300 oC and 650 oC); (2) phosphorus sorption and desorption studies on three constrasting soils amended with corn cob and rice husk biochar produced at 300 oC, 450 oC and 650 oC and (3) phosphorus fractions in corn cob and rice husk biochar produced at three pyrolysis temperatures (300 oC, 450 oC and 650 oC) as well as P fractions in biochar amended soils. In experiment 1, P removal ability of four biochar types namely cocoa pod husk, rice husk, corn cob and palm kernel shell produced at two pyrolysis temperatures (300 oC and 650 oC) was investigated by using series of batch experiments. Sorption isotherms and kinetics models were used to assess the removal ability and mechanism of P adorption on the biochar types. The effect of equilibrium pH on P sorption was also examined. Biochar types attained maximum P adsorption within equilibrium time of 6 to 12 h. The maximum adsorption capacity calculated from the Langmuir isotherm was from 4.12 to 13.02 mg g-1 in an increasing order of CP300 < CC300 < RH300 < CP650 < PK300 < CC650 < RH650 < PK650 for the studied P concentration ranged of 25- 200 mg P L-1. Generally, biochar types produced at 650 oC had higher P adosprtion capacity than at 300 oC. The equilibrium pH for maximum P adsorption varied among biochar types occurring in a range of 2.8 to 4.8. Increasing equilibrium pH decreases P adsorption. Freundlich isotherm coupled with pseudo second order and Elovich models explained the adsorption data well indicating a chemisorption process on heterogeneous surface of biochar involving ligand exchange (PK300, PK650, CP650), electrostatic attraction (RH300, CC300) and surface precipitation (CP300, CC650, RH650). Palm kernel shell biochar at 650 oC with the highest P sorption capacity should be the preferred choice for removal of the anion from wastewater. The CP300 having the least P adsorption capacity and with its high total P content, alkaline pH and the presence of carbonate could be exploited for use as a liming material on acid soils. In experiments 2 and 3, incubation studies were conducted for 80 d to investigate the effect of corn cob and rice husk biochar produced at three pyrolysis temperature (300 oC, 450 oC and 650 oC) on P sorption characteristics and fractions in two acid and one neutral soil. The P sorption capacity of the two acid soils i.e. Kokofu Series (384.6 mg kg-1) and Ankasa Series (333.3 mg kg-1) were about three fold more than the neutral soil (Keta Series) (104.2 mg kg-1). Amending the acid soils with biochar increased the equilibrium P concentration in solution at decreasing pyrolysis temperature for the two biochar types. There was, however, an increase in P sorption with increasing pyrolysis temperature in the neutral soil. The amount of P desorbed increased in the acid soils but decreased in the alkaline soil. Biochar produced at 300 oC had more significant effect on both the decrease in P adsorption and increase in P desorbability in the acid soils. The results of modified Hedley P fractionation showed that the most labile P (Resin-P, NaHCO3-Pi) and organic P pool showed a decreasing trend with increasing pyrolysis temperature in the biochar types. However, the Ca-bound P (HCl-Pi) and residual P increased with increasing pyrolysis temperature. The interaction of biochar with soils resulted in an increase in the most labile P as well as moderately P (NaOH-Pi) fractions in the three soil types making P more available for plant uptake. The increase in the readily available P pool was more significant at relatively lower temperature (300 oC) than higher pyrolysis temperatures for both biochar types. However, the increase in calcium-bound P and residual P of the soils was more predominant when both biochar types produced at 650 oC were applied. The study thus showed that biochar pyrolysed at 300-450 oC could be used to reduce P sorption and increase P bioavailability in acid soils. The addition of biochar to near neutral soils might increase P retention possibly in the short-term, reducing P bioavailability.Item An Investigation Of Agrochemical Transport Mechanisms In Some Cultivated Soils In Ghana(University of Ghana, 2015-07) Darko, D.A.The study basically examined the movement of agrochemical compounds in soil. Four different soil samples made up of three sandy loams and a sandy clay were used in the study. Potassium chloride solution and chlorpyrifos were used as infiltration solutions in a horizontal infiltration study under laboratory conditions. At the end of each experiment, the infiltration column was sectioned and the moisture content as well as the solution concentration of the agrochemical compound (Cl-, K+, and chlorpyrifos) contents determined. The water content, Cl-, K+ and chlorpyrifos contents profiles preserved similarity with regards to the variable . Moisture diffusivity and dispersion coefficients were therefore considered to be dependent on water content only. The moisture diffusivity function and the dispersion coefficients of the solutes were derived using the θ(λ) and c(λ) data together with the Continuous System Modeling Program (CSMP) computer program. The moisture diffusivity values obtained showed that the sandy loams due to their large pore sizes permitted higher infiltration of water than the sandy clay. With the exception of the Xanthic Ferrasol and Ferric Lixisol, which are sandy loam, the chloride profiles moved ahead of the profiles of water and the other solutes. The chloride concentration front measured in the Ferrasol and Lixisol lagged behind that of the water, thus suggesting chloride mobility was retarded during the infiltration experiment. Differences in the notional planes of chloride and water used as influent solutions in the infiltration experiments also suggests the existence of immobile water content in the sandy clay and one of the sandy loams. Estimation of the dispersion coefficient of chloride in the two soils in which immobile water content was established suggests that chloride dispersion was low when immobile water content was accounted for in the estimation of the dispersion coefficient.Item The Soil Meiqfauha of The Accra Plains(University of Ghana, 1997-12) Belfield, W; College of Basic and Applied Sciences ,School of Agriculture, Department of Soil ScienceSamples of soil have been taken from various situations at different times to illustrate the effects of season, water, sha.de, agriculture, disturbance and type of soil, on the soil meiofauna of the Accra Plains, It is shown that there is a significant difference both in numbers and in vertical distribution of the animals in different seasons and in different soils. Water is thought to be the most important factors as it is demonstrated that there is a direct correlation between size of population and the rainfall of the previous month, and that the vertical distribution can be correlated with the rainfall of the same month. Waterlogging however causes a reduction of population. Shade produces a marked effect on both the numbers and the vertical distribution, the population, with the exception of the Acarina, being smaller and deeper in exposed than in shaded bare fallow soil, ThiB is almost certainly caused by the desiccation conditions in the exposed soil. Disturbance of the soil by argicultural practices causes a reduction of population, and this smaller population persists during crop growing, and after harvest when, the plot is allowed to return to grass. Disturbance causes a rapid drying out of the soil, the crop does not give enough cover, ana harvesting causes impoverishment of the soil# Each of these conditions is shown to reduce the population* Different kinds of soil are shown to "be associated with a difference in sige and distribution of population. In both dry and wet seasons, the population of latosol is greatest* clay lowest and sand intermediate* During the dry season the population of latosol is found deeper than in the other two soils. It is suggested that this is because there is more food and water at lower levels in the latosol. This enables the animals to avoid the desiccation conditions in the upper layers, and to form a reservoir for a large population increase under the improved conditions of the wet season*Item Availability and uptake of iron: Effect of ph changes during uptake of macronutrient ions(University of Ghana, 1970-06) Adu, A.O.; Oertli, J.J.; Wallihan, E.F.; Page, A.L.; University of Ghana, College of Basic and Applied Sciences, School of Agriculture, Department of Soil ScienceLong-term greenhouse experiments with corn (Zea mays) established that uptake of Fe from nutrient solutions may be significantly enhanced by increasing the supply of potassium. A mechanism was proposed to describe how uptake of macronutrient ions may in turn influence availability and uptake of Fe and other elements from their chelated and sparingly soluble compounds. It was hypothesized that since differential accumulation of cations is accompanied by a net release of H ions, and excess anion accumulation accompanied by a net release of OH ions, uptake of Fe, for example, will be enhanced by increasing supply of salts favoring differential accumulation of cations: The released H ions will acidify the root free space, root surfaces, and the immediate root environment; minerals on root surfaces will be dissolved and chelated molecules will be dissociated; both reactions will liberate ions most of which will diffuse.through a relatively high H ion environment to absorption sites in the roots. The hypothesis was tested in short-term absorption experiments in which corn seedlings were allowed to absorb Fe from FeEDDHA or Fehydroxide sols in the presence of increasing concentrations of salts of K, Na, Li, Mg, or Ca. Uptake of Fe was highest in the presence of salts from which excess cation accumulation is known to occur and in which the largest pH drop was observed. Increasing the concentration of K, as KC1 or K2 SO4 , from 0.0 to 5.0 or 10.0 mM K in unbuffered solutions or exchange resin suspensions at pH >_ 6.9 resulted in considerable pH decline and increased Fe uptake. The pH decline correlated with the enhancement of Fe uptake. However, acidification to below pH of about 4.7 tended to reduce further Fe uptake. No detectable pH changes occurred in CaC0 3 plus Fe-hydroxide suspensions containing increasing supply of K, yet Fe uptake was enhanced during accumulation of K. Since essentially all Fe supplied as Fe-hydroxide occurred as colloidal particles or precipitates, enhancement of Fe uptake was attributed to a three-ion-contact effect: Plants accumulating excess cations released H ions which decomposed or dissolved the Fe sols or precipitates on root surfaces, thus freeing Fe ions for absorption. Theoretical calculations indicated that increasing H-ion concentration in the immediate root environment will significantly enhance liberation of Fe+ ^ from the stable chelate FeEDDHA. Old hypotheses claiming that potassium ions in plants are directly involved in reactions favoring translocation and utilization of Fe were replaced with one relating K uptake to subsequent reactions in the substrate.Item Diversity and Symbiotic Characteristics of Cowpea Brad Yrhizobium Strains in Ghanaian Soils(University of Ghana, 1999-08) Fening, J. OThis study reports investigation of the biodiversity of bradyrhizobia isolates that nodulate cowpea in Ghanaian soils. As a prelude, some components of nitrogen fixation of cowpea in the various soils were examined through: (1) assessment of the natural nodulation of 45 cowpea cultivars in 20 soils sampled from 5 ecozones (coastal savanna, tain forest, semi deciduous forest, forest savanna transition and guinea savanna), (2) determination of the numbers of bradyrhizobial isolates in the soils and (3) determination of the response of cowpea to nitrogen fertilization. The results of the ability of 45 cowpea cultivars to nodulate naturally in different soil types showed large variability among the cultivars. Counts of the indigenous bradyrhizobia population in the soils showed that most of the soils in Ghana harbour large populations of bradyrhizobia (in the range of 0.6 x 10 to 31 x 103) capable of nodulating cowpea. Response of cowpea to nitrogen fertilizer differed in the different soils. In general all the cultivars showed significant responses to increasing levels of nitrogen, an indication that nitrogen fixation was not supplying the plants with all the external nitrogen required for maximum yield. A combination of morpho-physiological and molecular analysis was used to assess the diversity of the bradyrhizobia isolates. A total of 100 isolates were assessed. The results of the morphophysiological analysis indicated that cowpea is nodulated by both fast and slow growing rhizobia. The results also showed that the isolates were versatile and could survive under different soil conditions particularly acidity and salt stress. A cross inoculation study of the isolates with nine legume species produced seven major groupings with 28 subgroups based on distinct nodulation patterns. Results of the serology (ELISA) assay indicated that only a small fraction of the isolates reacted strongly with antisera of each other. The greater proportion showed no cross reactivity. Analysis of the 16S rRNA gene of the isolates by PCR-RFLP identified 20 different composite genotypes. Diversity among the genomic species identified was very high, reaching 80% diversity. The various methods used indicated large diversity among the isolates, but the groupings of the isolates by the various methods were inconsistent, due to the different levels of resolution by the various methods. Diversity of the isolates in symbiotic effectiveness showed that some of the isolates had high nitrogen fixing capabilities that were comparable to plants fertilized with inorganic fertilizer nitrogen. Some of the isolates even showed superiority in symbiotic effectiveness relative to the standard strain TAL 169, suggesting that the native isolates may be useful strains for cowpea inoculation. The Gus A marker gene technique was used to assess the competitive abilities of the effective and ineffective isolates. Competition between the isolates was examined at different population ratios. The results obtained indicated that competitive ability was not directly related to effectiveness of strains. Inoculation of cowpea with indigenous bradyrhizobia isolates increased the number of nodules, shoot dry weight and total nitrogen of plants. The method of inoculation was observed to influence these parameters the results indicated that response of cowpea to inoculation in the presence of native rhizobia in some soils is possible.Item The Characteristics and Diversity of Indigenous Rhizobia that Nodulate Selected Indigenous Multipurpose Leguminous Trees and Shrubs in Three Soils of Ghana(University of Ghana, 2013-03) Boakye, E.Y.; Danso, S.K.A.; Offei, S.K.; Lawson, I.Y.D.Trees in general and leguminous trees in particular form an integral part of the traditional farming systems in Ghana. Compared to other plants, leguminous trees have the advantage that, they are generally capable of growing better on N-deficient soils due to their ability to convert unavailable atmospheric N 2 into plant utilizable N. However, several factors including the abundance and effectiveness of the specific rhizobial partner, the available N and P in soil, are among the important factors that severely affect how much N 2 can be fixed in these trees. This study was thus conducted to assess the abundance and characteristics of the rhizobia that nodulate 18 selected indigenous tree legumes grown in three representative soils of Ghana and to ascertain important soil nutrient constraints that affect their nodulation, nitrogen fixation and growth. The three soils belonged to the Hatso, Toje and Alajo local series (equivalent to Haplic lixisol, Rhodic lixisol and Calcic vertisol, respectively). The 200 Rhizobium isolates obtained from nodules of these tree legumes were found to be highly diverse and varied in their abilities to nodulate legumes other than the host plants from which they were isolated. The isolates were further characterized culturally, metabolically, phenotypically and for their effectiveness in fixing atmospheric nitrogen. Of the 10 multi-purpose shrubs and tree species belonging to the sub- family Mimosoideae examined as much as 70% of them formed nodules in the three soils, whiles only 20% and 10% of the tree legumes that formed nodules belong to Papilionoideae and Caesalpinoideae sub-families respectively. As to the Rhizobium isolates from these shrubs and tree species, those obtained from Pithecelobium spp and Melletia thonningi appeared to be highly specific, nodulating only their respective homologous hosts, while those from Acacia mangium, Albizia lebbek and Acacia auricloformis appeared to be slightly promiscuous, and moderately promiscuous for those from Leucaena leucocephela, Crotalaria ochloleuca, Cajanus cajan and Vigna unguiculata;, the NGR 234 strain, included as a standard was the most promiscuous, forming nodules on almost 67% of the eight host legumes on which it was tested. With regards to the occurrence of rhizobia in each soil, the three soils were found to harbour variable populations of indigenous rhizobia, ranging from 22 cells/g of soil for A. mangium and C. ochloleuca in Alajo soil, to 5,200 cells/g for compatible strains of Pithecelobium sp. (in each of the three soils), M. thonningi (in Toje and Hatso soils) and A. lebbek (in only the Hatso soil). Further examination of the characteristics of the Rhizobium isolates revealed that each shrub and tree legume species was nodulated by strains belonging to both the fast-growing (Rhizobium) and slow-growing (Bradyrhizobium) types. In terms of abilities to fix N 2 , the greatest majority (63%) of the isolates were found to be ineffective on their homologous host plants, with ineffectiveness ranging from 43% of the Acacia auricloformis strains to 88% of isolates from Acacia mangium. The proportion classified as being effective averaged 15% and ranged from 5% in the case of Acacia mangium to 28% of the Albizia lebbek isolates. The polymerase chain reaction (PCR) of the 16S rRNA gene of almost all the 60 selected Rhizobium isolates from the tree legumes gave a single band of size 1.5 kb, corresponding to the expected band size reported for rhizobia, while the combined restrictions of the 16S rRNA genes of the 60 rhizobia isolates with five enzymes (Hae 111, Rsa 1, Hpa 1, Hpa 11 and Alu 1) distinguished clearly 60 different combinations of patterns or fingerprints, representing 60 distinct 16S rRNA genotypes among the isolates. Characterization of the test rhizobia isolates based on simple PCR of the intergenic spacer (ITS) gene was most resolute as it provided several distinct band sizes indicating great variation among the rhizobia isolates’ ITS. However, restriction of the ITS with three restriction enzymes (Hae 111, Hpa 11 and Alu 1) did not give much further distinctions among the test isolates. Experiments conducted in pots in the screenhouse using the Hatso and Toje soils indicated significant increases in both number of nodules formed, N 2 fixation and total biomass of A. lebbek, A.mangium and A. auricloformis with P addition to soils. However, the application of phosphorus beyond 90 kg P/ha resulted in significant decrease in all these parameters in Hatso and Toje soils. With nitrogen fertilizer application, even the minimum level (40 kg N/ha) resulted in significant reduction in numbers of nodules formed on the tree legumes, even though it resulted in significant increase in plant biomass. However, phosphorus application mitigated the negative effect of nitrogen addition. Rhizobium inoculation also resulted in significant increase in both number of nodules formed and total biomass of the tree legumes over the uninoculated controls. Thus although the rhizobia that nodulate tree legumes in Ghanaian soils may be widespread, the rhizobia that occur in each soil appear to be heterogeneous or very diverse both phenotypically and genotypically and in their abilities to form effective nodules. To enhance nodulation, nitrogen fixation and growth of the tree legumes, consideration must be given to augmenting these soils with selected, highly effective strains together with phosphorus fertilizer.