Yield response of soybean and cowpea to rock phosphate fertilizer blend and rhizobial inoculation on two benchmark soils of northern Ghana

Two field experiments were conducted on a Gleyic Lixisol and a Ferric Luvisol at Bontanga and Nyankpala, respectively during the 2012 and 2013 cropping seasons. The aim of the study was to assess the effects of Rock Phosphate Fertilizer Blend (RPFB) and rhizobial inoculation on yield of soybean and cowpea. The effect of combined application of low rates of nitrogen fertilizer and RPFB on N and P uptake in soybean and cowpea were also determined. The experiments were laid out in a randomized complete block design with split-plot arrangement of the treatments which were replicated three times. At each experimental site, inoculated (+Rh) and uninoculated (-Rh) treatments constituted the main plots. The following treatments were assigned as sub-plots on the Gleyic Lixisol at Bontanga: To = 0 kg P2O5 ha -1 ; T1 = RPFB 34.35 kg P 2O5 ha -1 ; T2 = RPFB 68.70 kg P 2O5 ha -1 ; T3 = TSP 34.35 kg P 2O5 ha -1 and T 4 = TSP 68.70 kg P 2O5 ha -1 while To = 0 kg P2O5 ha -1 ; T1 = RPFB 68.70 kg P2O5 ha -1 ; T2 = TSP 68.70 kg P 2O5 ha -1 + 25 kg N ha -1 ; T3 = TSP 68.70 kg P 2O5 ha -1 and T4 = RPFB 68.70 kg P 2O5 ha -1 + 25 kg N ha -1 constituted the sub-plots on the Ferric Luvisol at Nyankpala. Phosphorus fertilizer application and rhizobial inoculation increased soybean nodulation on the Gleyic Lixisol. Application of TSP 34.35, 68.70 and RPFB 68.70 kg P 2O5 significantly increased nodule dry weight of soybean while cowpea nodule dry weight increased with the application of TSP 68.70 and RPFB 34.35 kg P2O5 . The application of TSP 68.70 kg P 2O5 fertilizer significantly increased soybean shoot dry matter yield by 84% while RPFB 68.70 kg P 2O5 gave an increase of 25% relative to the control. Similarly, cowpea shoot dry matter yield increased by 81 and 67% due to application of TSP and RPFB, respectively compared to the control. The TSP xviii 68.70 kg P 2O5 + 25 kg N and RPFB 68.70 kg P 2O5 + 25 kg N treatments also increased soybean grain yield on the Ferric Luvisol by 74 and 9%, respectively over the control while that of cowpea was increased by 53 and 51%, respectively . Soybean grain N and P uptake on the Ferric Luvisol were significantly increased by 78 and 120%, respectively over the control as a result of the application of TSP 68.70 kg P 2O5 + 25 kg N. Application of RPFB 68.70 kg P 2O5 + 25 kg N did not significantly increase soybean grain N and P uptake. Cowpea grain N and P uptake were also increased by 40 and 81%, respectively over the control due to application of TSP 68.70 kg P 2O5 + 25 kg N. The RPFB 68.70 kg P 2O5 + 25 kg N treatment gave an increase in grain N and P uptake of 44 and 74%, respectively over the control. Value-cost ratio analysis indicated that TSP 68.70 kg P 2O5 + 25 kg N is a promising treatment combination for profitable soybean and cowpea production on the Ferric Luvisol than RPFB 68.70 kg P 2O5 + 25 kg N. Results of this study have shown that, application of triple superphosphate and 25 kg N better enhances soybean N and P uptake than rock phosphate fertilzer blend. For cowpea, application of both triple superphosphate and rock phosphate fertilizer blend equally enhanced grain N and P uptake. The study further revealed that in the short term, application of TSP 68.70 kg P 2O5 + 25 kg N on the Ferric Luvisol is more profitable for soybean and cowpea production than RPFB 68.70 kg P 2O5 + 25 kg N

Source: KNUST