Influence of phosphorus fertilizer blends on insect pest incidence, yield and profitability of soybean production in the Guinea Savannah agro-ecological zone of Ghana

Field studies were conducted to test the effects of different fertilization regimes on insect pest abundance and grain yields of soybean, as well as on their profitability in the Guinea Savannah zones of Ghana. A total of five fertilization regimes were tested, and these were: 250 kg ha-1 TSP (46% P2O5 or 20%P) applied at sowing; 250 kg ha-1 YARA Legume II (4%N, 7.9%P, 10.8% K, 31%CaO (insoluble), 6%CaO (soluble), 3% MgO, 3%S, 0.075% B) applied at sowing; 250 kg ha-1 YARA Legume II applied at four weeks after sowing (WAS); 65kg ha-1 Nitrabor (15.45% N, 26%CaO, 0.3 B) applied at sowing plus 185 kg ha-1 YARA Legume I (0 % N, 7.9% P, 10.8% K, 31% CaO (insoluble), 4%S, 2% MgO) applied at 4WAS; 185 kg ha-1 YARA Legume I applied at sowing plus 65 kg ha-1 Nitrabor applied at 4WAS. The experiments were laid in randomized complete block designs with three replicates. Fertilization enhanced soybeans’ ability to overcome pest infestations, with plants treated with Nit-65+YLI-185 and YL II-250 + 0 Fert recording lower pest populations and significantly lower pest damages compared to the unfertilized plot. Fertilizer application increased soybean yield by 2269 kg ha-1 in the on-station experiment and by 1334 kg ha-1 in the on-farm experiment. In the on-station experiment, fertilizer use efficiency ranged from 5.5 kg grain per kg fertilizer applied at the 250 kg ha-1 YARA Legume II at 4 WAS to 12 kg grain per kg fertilizer applied with the 65kg ha-1 Nitrabor at sowing plus 185 kg ha-1 YARA Legume I at 4WAS. A similar observation was made in the on-farm experiment but with lower values. Phosphorus use efficiency followed a similar pattern as in the fertilizer use efficiency in both the on-station and on-farm experiments. The highest value cost ratio was attained with 65kg ha-1 Nitrabor at sowing plus 185 kg ha-1 YARA Legume I at 4WAS treatment in both the on-station and on-farm experiments, indicating the potential of increasing the productivity of soybean and the income of farmers in northern Ghana through the regime of fertilization.