Soybean Yield and Chemical Composition in Response to Phosphorus–Potassium Nutrition in Kashmir

Soybean [Glycine max (L.) Merr.] has increasing nutritional, commercial, and economical value, and P and K nutrition may be needed to increase yield and profit. A 2-yr (2008–2009) field experiment with rainfed soybean was conducted in the hilly region of the state of Azad Jammu and Kashmir (AJK), at Rawalakot, Pakistan. The aim of the study was to evaluate the effects of P–K fertilization on soybean root nodulation, seed yield, seed composition and N, P, and K uptake. The experiment was conducted in a randomized complete block design with three replications. Treatments included three levels of P (60, 90, and 120 kg P2O5 ha−1), two levels of K (40 and 80 kg K2O ha−1), and a control, represented as P0, P60, P90, P120 and K0, K40, and K80, respectively. Results indicated that number of root nodules increased with P–K fertilization to 75 and 136 compared with 68 in the control. Yield responses to P–K fertilization occurred to all rates, and the highest yield was observed in the combined treatment of P120K40. Total N, P, and K uptake in the plant (shoot + seed) tended to follow yield responses, while seed protein was increased by 8 to 13% due to P and 11 to 19% due to K. Application of P or K alone or in combination significantly increased oil content. This study demonstrates that P- and K-deficient soils are likely to produce crops with low yields and low seed oil levels, and appropriate P–K management could be an effective approach to increase and sustain soybean production in the mountain ecosystems.