College of Agriculture & Natural Resources

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Optimizing legume-rhizobia symbiosis to enhance legume grain yield in smallholder farming systems in Ghana
(May, 2018.) Ulzen, Jacob
Soybean and cowpea yields on smallholder farms in northern Ghana are far below the potential yield creating a huge yield gap. This thesis reports on a series of experiments aimed at improving the productivity of soybean and cowpea using effective and persistent strains, as key determinant, within an integrated soil fertility management framework to bridge the yield gap. The field experiments conducted mainly on smallholder farms at Kpachi, Kpalga, Tunayilli, Nyagli, Tanina and Busa in the northern part of Ghana addressed issues of persistence of Bradyrhizobium strains, the response to the application of phosphorus, organic manure, and Bradyrhizobium inoculation singularly or in various combinations using soybean and cowpea as legume hosts in four different studies. The economic benefits of these interventions were also evaluated using value cost ratio (VCR). Four different Bradyrhizobium strains; 532 C (in Legumefix), USDA 110 (in Biofix) and BR 3267 and BR 3262 evaluated for their symbiotic effectiveness on soybean and or cowpea, significantly increased yield over the uninoculated control treatment at Nyankpala but not Nyagli. USDA 110 inoculation of soybean resulted in grain yield 1.5 fold that of 532 C. Strain BR 3267 increased grain yield of cowpea (>2 folds) relative to BR 3262. USDA 110 and BR 3267 were found to be economically profitable with VCRs of 8.7 and 4.6, respectively at Nyankpala. The persistence of B. yuanmingense strain BR 3267 and B. japonicum strain USDA 110 were monitored over a period of 296 days. At 296 days, the numbers of surviving cells of B. yuanmingense strain BR 3267 and B. japonicum strain USDA 110 were log10 1.9 and log10 1.7, respectively. Native Bradyrhizobia population and soil moisture were the predominant factors that influenced the survival of the introduced strains. Addition of P and organic manure (fertisoil and cattle manure) improved cowpea response to Bradyrhizobium inoculation in a cross factorial experiment. Yield increases of 1427 and 1278 kg ha-1 were obtained over the control (without an amendment) when fertisoil and cattle manure with P, respectively were applied in combination with Bradyrhizobium inoculant. The addition of P and Bradyrhizobium inoculant to organic manure was profitable with a VCR of 2. In a single non-replicate trial to test soybean response to P and/ or Bradyrhizobium inoculant (I), a greater yield response of 1371 kg ha-1 was obtained by I+P in the study locations in the Northern region. Both P and I significantly increased grain yield by 17 and 22% respectively over the control. In the Upper West region, yields were relatively low ranging from 128 (control) to 227 kg ha-1 (P+I) in the study locations. Nonetheless, a huge variability in soybean grain yield response to P and / or I was observed in individual farms. Soil nitrogen, phosphorus, cumulative rainfall, soil type, organic carbon, pH and texture explained 42-79 % of the variability in yield in the Northern and Upper West regions. About 75% of the farmers who applied inoculant alone obtained VCR ≥ 1 and 64% of the farmers who applied inoculant in combination with P had VCR ≥ 1. These results imply that Bradyrhizobium inoculation is an effective strategy for increasing grain yield of soybean and cowpea for smallholder farmers. Greater benefits were obtained when inoculants were applied in combination with P and/ or organic manure (fertisoil and cattle manure) and can thus be recommended as soil management option for farmers. These results have important implications for policy makers, government and non government organizations in their quest to bridge the yield gap and improve livelihood for smallholder farmers.
Quantifying Soil and Nutrients Losses under Different Soil Amendments and Cropping Systems on a Plinthic Vetic Lixisol in Ghana
(May, 2018) Bigabwa, Janvier Bashagaluke
Soil erosion coupled with soil nutrients depletion affect crop production in small-scale cropping systems of sub-Saharan Africa (SSA). Reducing both threats, based on sustainable practices is crucial to enhancing crop productivity in the region. The current study was designed to help address the twin problems based on the following objectives: (i) developing and validating a new numerical method for surface runoff assessment; (ii) determining the effect of crop and soil management practices on soil loss; (iii) analyzing soil nutrients loss due to soil erosion under different amendments and cropping systems; (iv) assessing the effect of soil amendments and cropping systems on soil properties; (v) assessing the effect of soil amendments on crop productivity. In achieving these objectives, a field experiment was carried out on runoff plots under different cropping systems (commonly practiced in Ghana) treated with soil amendments. The study was a two-factor experiment in split-plot arranged in a randomized complete block design for three consecutive cropping seasons (2016 major, 2016 minor and 2017 major seasons). The cropping systems (sole maize, maize intercropped with soybean, sole soybean and cowpea) constituted the main plots whereas the subplots comprised soil amendments (inorganic fertilizers (NPK), inorganic fertilizers combined with biochar (NPK+BC), sole biochar (BC) and control). For the model development and soil erosion characterisation, a total of 33 erosive rainfall events were observed. Different statistical parameters viz. p-values, R², RMSE, NSE and RSR were used to assess the quality of the model developed. Parameters on the effects of the soil and crop management practices were analyzed in ANOVA and regression models. P value < 0.001 and R² ranging from 0.88 to 0.94 showed good accuracy of the model prediction. The dispersion between the predicted and observed values was low with RMSE varying from 1.68 to 2.66 mm. Moreover, the low variability between parameters was confirmed with the low values of RSR which ranged from 0.38 to 0.46 (with 0.00 ≤ RSR ≤ 0.50 for good prediction). During the observation periods, NSE values ranged from 0.79 to 0.86 (≥0.75 being the threshold for excellent prediction). The sensitivity analysis showed that the model under high runoff generation (simulation including bare plots), was poorly adapted. Results for crop yield and soil properties showed positive impacts of the different interventions. Soil loss characteristics based on amount of soil loss, soil depth reduction and runoff coefficient were significant (P < 0.05). Among the different treatments, sole cowpea and inorganic fertilizers application were most effective in reducing soil erosion. Also, biochar, due to its multipurpose effect on soil properties, had positive effects on soil erosion reduction compared to the control. Cumulative nutrients loss, enrichment ratios and monetary values of soil nutrients loss varied significantly under the amendments and cropping systems. Soil nutrients loss was more pronounced on the bare and the control plots than on the treated plots due to less soil erosion from the latter. All the nutrients had enrichment ratios (ER) greater than unity showing off-site nutrients deposition due to soil erosion; and this was more pronounced during the minor season than in the major seasons. The soil particles had ER greater than unity, except for the sand with values ranging from 0.77 to 0.88 and from 0.65-0.70 in the major and minor seasons, respectively. The economic effect of soil erosion based on the monetary values of soil nutrients loss was high for the control plots for each cropping system followed by the sole biochar (BC) treatment. Monetary loss under NPK and NPK+BC treatments was lowest due to their positive impacts on soil erosion reduction. The physical soil properties (bulk density and volumetric moisture content) were improved by the different practices and best values were observed under sole cowpea and sole biochar with respect to the cropping systems and soil amendments. Soil acidity increased slightly over time except under biochar treatments where a slight decline was observed. The legume-based cropping systems as well as the inorganic fertilizers applications improved soil organic carbon, total nitrogen, available phosphorus and exchangeable potassium contents slightly than the other treatments. For all the three crops evaluated (maize, cowpea and soybean), the productivity (grain and biomass yields) was better under the inorganic based treatments followed by sole biochar. Land equivalent ratio (LER) was greater than 1 under all the amendments under the maize-based systems. This emphasized the positive effect of the intercrop compared to the sole systems. With respect to cost effectiveness, VCR was greater than 2 for only sole NPK treatments under all the cropping systems and also for sole biochar treatment during the third season (2017 major). However, for NPK+BC, VCR > 2 was observed under the intercropped system throughout the study period. Indeed, sustainable nutrients management systems reduced soil loss and enhanced crop productivity and are recommended for small-scale farming activities in SSA.
Assessing the effectiveness of native Rhizobia as potential strains for local inoculant production for enhanced cowpea and groundnut yields in northern Ghana
(October, 2018) Osei, Ophelia
Efficient exploration of the legume-rhizobium symbiosis via inoculation with rhizobia is constrained by the limited knowledge on the fate of introduced strains under field conditions and the unavailability of effective native strains for use as local inoculants. This research therefore sought to address these challenges in four studies: i) nodule occupancy determination ii) identification of effective native isolates iii) symbiotic performance evaluation of elite native isolates under field conditions and iv) assessment of the persistence of elite isolates following field inoculation. Significant differences (p< 0.05) in shoot biomass of cowpea following inoculation was observed. The differences were explained via nodule occupancy studies by designing specific primers for the test strain Bradyrhizobium pachyrhizi BR 3262 (a recommended cowpea strain in Brazil) using the comparative genomics approach. Out of eleven specific primer pairs designed, the primers 2645 and 2736 were observed to be highly sensitive and reliably detected the target strains in nodules extracts of gnotobiotic system and potted soil grown cowpea. These two primers are thus novel tools for determining the fate of BR 3262 in field inoculation studies. The approach for designing specific primers in this study should be applicable to other bacteria/rhizobium strains whose genomic sequences are available. Bioprospecting for nodules of groundnut and cowpea cultivated in farmers’ fields without inoculation was done followed by isolation of rhizobium in the laboratory. Authentication and symbiotic effectiveness evaluation of the isolated rhizobium strains led to the selection of seven effective isolates. The nitrogen accumulated via BNF of the selected effective isolates was significantly higher (p< 0.05) compared to the –N control treatment. Treatment with isolate KNUST 1002 resulted in a total N accumulation that was comparable to the reference strain 32H1 on groundnut (BR 1 variety) grown in potted soils. Genetic characterization of the seven effective isolates revealed them as diverse with isolates KNUST 1003 and KNUST 1007 belonging to the Rhizobium tropici speices. The five remaining isolates were identified to belong to the Bradyrhizobium yuanmingense species. The two most effective isolates were evaluated in the field alongside a positive (with nitrogen) and negative (without nitrogen or inoculation) control on cowpea (Songotra variety) and groundnut (Chinese variety) in multi-locational trials in the Northern region of Ghana using the randomized complete block design. On the average, cowpea grain yields produced by the inoculated treatments were significantly (p< 0.05) larger than the –N treatment. Isolate KNUST 1002 produced the best average yield (1056 kg ha-1) which was significantly different from the other treatments. Groundnut yields on the other hand were significantly larger with isolate KNUST 1006 (1234 kg ha-1). The chemical properties of soils in the study locations generally showed low soil fertility. The different soil types significantly influenced the performance of treatments across the study locations. Twenty-six and 23% of the variability in grain yields of cowpea and groundnut respectively, was explained by the soil type and treatment interaction. These results imply that effective native isolates in this study can improve grain yields of cowpea and groundnut based on location specific recommendations. The persistence of effective isolates following previous inoculation on cowpea and groundnut was assessed in the 2017 cropping season on ten of the sites considered in 2016. Nodulation in both previously inoculated and re-inoculated plots were significantly higher than the un-inoculated plots (+N and –N). Nodule dry mass recorded for isolate KNUST 1006 in previously inoculated plots did not differ significantly from that of re-inoculated plots on both target host. However, the nodule dry mass recorded for isolate KNUST 1002 on cowpea in previously inoculated plots was significantly lower than in re-inoculated plots. Increases in grain yield of groundnut were significantly larger for treatment with isolate KNUST 1006 than the other treatments for previously inoculated and re-inoculated plots. Isolate KNUST 1002 on cowpea produced significantly higher yields than the other treatments in previously inoculated and re-inoculated plots. The type of legume host in each case influenced the performance of the isolates. There were no significant differences in the yields produced by either of the isolates in previously inoculated and re-inoculated plots. These results indicate that effective native isolates persisted and effectively nodulated the target legumes obviating the need for re-inoculation in subsequent cropping season. The outcomes of these studies have important implications for the use of effective isolates from this study as inoculants to improve cowpea and groundnut yields particularly in Northern Ghana.
Impact of Arbuscular Mycorrhizal Fungi Inoculation on Soybean (Glycine max) Production in the Semi-Deciduous Forest Zone of Ghana
(May, 2018) Thioub, Malamine
Phosphorus (P) is an important but limiting major nutrient in crop production. Its availability in the soil and consequently for plant nutrition remains a major challenge. The overall aim of this study therefore was to assess the potential of four arbuscular mycorrhizal fungi (AMF) isolates in enhancing mineral P fertilizer use efficiency in soybean and their beneficial residual effects on succeeding maize crop. Two pot experiments were conducted under greenhouse conditions using sterile river sand and a non-sterile soil on which two soybean lines (TGx 1989-48 FN and TGx 1989-75 FN) were evaluated. The soybean lines were inoculated with the four mycorrhizal isolates (Glomus etunicatum, G. fasciculatum, G. mosseae and Rhizophagus irregularis) as a preliminary screening study to select the top 50% symbionts. A factorial arrangement using a completely randomized design was used. Furthermore, a two-year field experiment was also conducted following the screening study during the minor and major cropping seasons of 2016 and 2017 respectively to evaluate the potential of combined mycorrhizal inoculation and P mineral fertilizer in enhancing soil P availability, soybean growth and yield and economic profitability. The two aforementioned soybean lines used in the pot experiments were separately inoculated with the top 50% mycorrhizal isolates (G. mosseae and R. irregularis). An uninoculated control treatment was included. Triple superphosphate (TSP) was applied at three levels (0, 15 and 30 kg P ha-1). A split-split plot design with three replications was used; soybean lines as the main-plot factor, TSP rates as the sub-plot factor while the AMF isolates constituted the sub-sub plot factor. In a separate experiment, an early maturing maize variety (Omankwa) was planted following the minor cropping season of 2017 to evaluate the residual effects of the imposed treatments on root length colonization, N and P uptake, shoot biomass and grain yields. The greenhouse study revealed that R. irregularis and G. mosseae improved P uptake, plant height, stem girth and shoot biomass yield of soybean relative to G. etunicatum and G. fasciculatum. In the field experiment, inoculation with the selected AMF isolates combined with 15 kg P ha-1 resulted in the highest soybean root length colonization, P use efficiency, shoot and grain P uptake, plant height, shoot biomass and grain yields. Furthermore, AMF + 15 kg P ha-1 reduced soil microbial biomass P by stimulating P release by soil microbes and thus increased soil available P. Again, G. mosseae showed higher performance in soybean root length colonization and P uptake, which reflected in the better growth and yield improvement than R. irregularis. The economic analysis indicated that inoculation using the selected mycorrhizal isolates combined with 15 kg P ha-1 had the highest net benefit and marginal rates of return and is therefore economically more profitable for soybean production. Glomus mosseae, underfield conditions persisted even after two cropping years. Maize root length colonization was higher in plots previously inoculated with AMF, which reflected in highest maize shoot N and P uptake, grain P uptake, shoot biomass and grain yields relative to the control. This study established that, the appropriate management of AMF inoculation is a potential to reducing the use of inorganic P fertilizers.
Optimizing Manure Quality for Increased Food Production on Small Holder Farms in the Upper East Region of Ghana
(SEPTEMBER, 2009) Ewusi-Mensah, Nana
The beneficial role of cattle manure to improving soil fertility has long been recognized. Its uses however have several drawbacks. One of such drawbacks is the nutrient content which is generally low and variable depending on the feed of the animal and manure management. This study focused on improving the quality of cattle manure for increased maize yields and consisted of five parts: 1. Assessment of the resource quality of cattle manure in seven districts of the Upper East region. 2. Composting of cattle manure. 3. Laboratory - incubation studies to determine nutrient release patterns of compost. 4. Field decomposition studies of buried compost in litter bags. 5. Assessment of the effects of compost, cowdung and NPK fertilizer on crop growth and yield. A survey was conducted in seven districts of the Upper East region using structured questionnaires to seek information on management practices likely to influence manure quality such as storage and handling. The survey revealed that nitrogen losses up to 100% were sometimes obtained by the time the manure was incorporated into the soil. An initial resource quality analysis of the manure sampled from the seven districts was conducted in the laboratory using standard protocols. The results indicated that N and P contents of the manure ranged from 0.27 to 1.14% and 0.28 to 0.76% respectively, which were all below the critical levels for net mineralization. Polyphenol levels on the other hand were lower than the critical value of 4%. Decomposition and nutrient release from the manure showed immobilization of total N during the first four weeks, suggesting the need to improve the quality by composting or by applying it in combination with mineral fertilizers. In an attempt to improve the quality of the manure, composting with Stylosanthes guinensis using the aerated pile method was carried out. Two main compost types (1:1 and 2:1 ratios of cowdung to plant material) were prepared. Total N and P contents of the composts at the end of study period ranged from 1.10 to 1.46% and 0.28 to 0.31% respectively. Mineralization studies on the resultant composts were conducted under laboratory (leaching tube method) and field (litter bag technique) conditions. Under laboratory conditions, both compost types showed net N and P immobilizations during the first two weeks of incubation. However, under field conditions, net N and P mineralization rates were observed throughout the study period for both compost types. Half life values (time required for 50% of the initial mass to decompose) of 8 and 10 days respectively were recorded for the 1:1 and 2:1 compost types. Furthermore, the 1:1 compost had a higher decomposition rate constant (k = 0.085) than the 2:1 compost (k = 0.056). In all cases, negative correlations were observed between the mass of composts remaining and nutrient released. The contribution of the composts to improving the fertility of the soil and hence crop growth was evaluated by comparing maize response to various rates of the composts with optimum mineral fertilizer combinations. The results showed that the 1:1 compost treatment at 3 t/ha, produced the highest maize grain yield (4.99 t/ha). Maize grain yields obtained from both compost types compared very well with NPK fertilizer suggesting that composting of cattle manure with Stylosanthes guinensis enhanced its quality and nutrient release potential for increased crop yield.

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