Groundnut yields obtained by farmers in northern Ghana are generally low due to low soil fertility resulting from continuous cropping coupled with low use of external inputs. There is therefore the need to use systems’ internal resources such as biological nitrogen fixation efficiently to enhance crop production. This on-station experiment investigated nodulation and pod yield responses of three groundnut varieties, namely Obolo, Oboshie and Samnut 22 to inoculation with rhizobium inoculants of exotic strains, namely Bradyrhizobium yuanmingense (BR 3267) and USDA 3456 in combination with 0 kg P ha−1, 15 kg P ha−1 and 30 kg P ha−1. Combined application of 30 kg P ha−1 and BR 3267 increased the nodule numbers in Obolo, Oboshie and Samnut 22 by 144%, 188% and 56%, respectively compared to their uninoculated counterparts. Inoculation with BR 3267 produced the highest pod yield in all the three varieties with yields increasing from 13 to 40% over that of the uninoculated treatments, with BR 3267-inoculated Samnut 22 giving the highest yield of 2013 kg ha−1. P fertilizer and rhizobium inoculant also had a significant interactive influence on the pod yield of groundnut. Combined application of 30 kg P ha−1 and rhizobium inoculation increased the groundnut yield by 64 to 68%. The study observed a positive interaction between the rhizobium strains and P fertilizer.

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Farmers in the inland valleys of northern Ghana are challenged with nitrogen (N) deficiency as a major production constraint of rainfed lowland rice (Oryza sativa L.). With extremely low use of external inputs, there is a need to efficiently use the systems' internal resources such as native soil N. Largest soil nitrate‐N losses are expected to occur during the transition between the dry and wet season (DWT) when the soil aeration status changes from aerobic to anaerobic conditions. Technical options avoiding the build‐up of nitrate are expected to reduce N losses and may thus enhance the yield of rice. A field study in the moist savanna zone of Ghana assessed the in situ mineralization of native soil N, the contribution of nitrate to the valley bottom by sub‐surface flow from adjacent slopes, and the effects of crop and land management options during DWT on seasonal soil Nmin dynamics and the yield of lowland rice. Large amounts of nitrate accumulated during DWT with a peak of 58 kg ha−1 in lowland soils, of which 32 kg ha−1 were contributed from the adjacent upland slope. Most of this nitrate disappeared at the onset of the wet season, possibly by leaching and denitrification upon soil flooding. While the incorporation of rice straw (temporary immobilization of soil N in the microbial biomass) had little effect on soil N conservation, growing a crop during DWT conserved 22–27 kg of soil N ha−1 in the biomass and Crotalaria juncea supplied an additional 43 kg N ha−1 from biological N2 fixation. Farmers' practice of bare fallow during DWT resulted in the lowest rice grain yield that increased from 1.3 (2.2) to 3.9 t ha−1 in case of the transition‐season legume. Growing a pre‐rice legume during DWT appears a promising option to manage N and increase lowland rice yields in the inland valleys of northern Ghana.

A discrete number of studies have been conducted on the effects of rhizobia (Rhz) inoculants, phosphorus (P) management, and combined application of Rhz and P fertilizer on the enhancement of grain legume yield across soils of Ghana and elsewhere. However, the extent to which the various inoculated Rhz strains, P application, and combined application of Rhz + P studies contribute to improving yield, performed on a comprehensive analysis approach, and profit farmers are yet to be understood. This study reviewed different experimental studies conducted on soybean (Glycine max (L.) Merr.), cowpea (Vigna unguiculata [L.] Walp), and groundnut (Arachis hypogaea [L.]) to which Rhz inoculants, P supplements, or Rhz + P combination were applied to improve the yield in Ghana. Multiple-step search combinations of published articles and multivariate analysis computing approaches were used to assess the effects of Rhz inoculation, P application, or both application of Rhz and P on yield variation. The random forest (RF) regression model was further employed to quantify the relative importance of various predictor variables on yield. The meta-analysis results showed that cowpea exhibited the highest (61.7%) and groundnut (19.8%) the lowest average yield change. The RF regression model revealed that the combined application of Rhz and P fertilizer (10.5%) and Rhz inoculation alone (7.8%) were the highest explanatory variables to predict yield variation in soybean. The Rhz + P combination, Rhz inoculation, and genotype wang-Kae explained 11.6, 10.02, and 8.04% of yield variability for cowpea, respectively. The yield in the inoculated plants increased by 1.48-, 1.26-, and 1.16-fold when compared to that in the non-inoculated cowpea plants following inoculation with BR 3299, KNUST 1002, and KNUST 1006 strains, respectively. KNUST 1006 strain exhibited the highest yield increase ratio (1.3-fold) in groundnut plants. Inoculants formulation with a viable concentration of 109 cells g−1 and a minimum inoculum rate of 1.0 × 106 cells seed−1 achieved the highest average yield change for soybean but not for cowpea and groundnut. The meta-analysis calls for prospective studies to investigate the minimum rate of bacterial cells required for optimum inoculation responses in cowpea and groundnut.

Phosphorus (P) deficiency is a major constraint to upland rice production on highly weathered, low activity clay soils in the humid zones of West Africa. There is a paucity of information on the short-term fertilizer P effects on rice on these soils. A field experiment was conducted in 2011 to determine the response of twenty-four (24) upland rice cultivars to fertilizer Phosphorus (P) applied at 0 and 60 kg P ha −1 . An uncultivated field at SARI research area with available P (Bray 1) P content of 3.0 mg/kg was used for the experiment.The ploughed area was divided into two plots with one plot for +P and the other for -P treatment. Each of the 24 varieties was allocated three rows and spaced at 20 x 10 cm in four replications. The varieties were randomized for each replicate and planted on 2 nd July 2011 at one seed per hill. Pre-emergence herbicide Pendimethaline 400 g/l (Alligator) was applied at 3.2 L/ha two days after planting followed by one hand weeding. For the (-) P plot, the entire field received N at 60 kg/ha as Sulphate of ammonia and K 2 O at 60 kg/ha as Muriate of Potash. For the (+) P plot, fertilizer was applied at NPK 60-60-60 kg/ha from Sulphate of ammonia, Triple superphosphate and Muriate of potash, respectively. For each plot, the N was split applied.Results showed that the plants that received P were more vigorous and healthier. There was significant variety effect on number of tillers per plant (NOTPP), days to 50% flowering (DFF), days to maturity (DTM), dry weight of biomass (DWOB), number of panicles per plant (NOPPP), and grain yield per plant. Similarly, there was significant phosphorus effect on number of tillers per plant (NOTPP), days to 50% flowering (DFF), days to maturity (DTM), dry weight of biomass (DWOB), number of panicles per plant (NOPPP), and grain yield per plant. There was generally no interactive effect of variety by fertilizer except for DFF and DTM. The number of tillers per plant ranges from 3 -16 with the overall mean without P application being 4 while overall mean with P application was 9. When P was applied, the number of days to 50 % flowering reduced from 86 days to 79 days. Days to maturity (DTM) was also reduced from 118 to 111 on average by P application. The varieties that were most tolerant to low P were ITA 257, Nerica 3 and TOX 1011-4-A2. The grain yield of ITA 257 remained the same whether P was applied or not. This is the variety that is best adapted to low P. We concluded that rice growth and yield components were affected by Phosphorus application. Plants that received phosphorus flowered and matured earlier. They also accumulated higher biomass and grain yield. ITA 257, Nerica 3 and TOX 1011-4-A2 were most tolerant to P deficiency.