Phosphorus fertilizer response in an irrigated soybean-wheat production system on a subtropical, semiarid soil

Development of high yielding mosaic-resistant varieties of soybean (Glycine max L.) has led to a substantial increase in area under soybean cultivation in rotation with other crops under irrigated conditions in subtropical regions of south Asia. Information on the fertilizer P requirement of soybean-grown in double-cropping annual rotations involving crops such as wheat (Triticum aestivum L.) is lacking but needed for developing P management strategies. Two field experiments were conducted for 4 years on a semiarid irrigated Tolewal sandy loam soil (Typic ustochrepts) in northwest India. The purpose of the experiments was to evaluate the effect of different rates of fertilizer P-applied in three frequencies representing direct, residual and cumulative P-treatments on crop yields, P uptake, fertilizer P use efficiency and fertilizer P recovery by a soybean-wheat production system. Soybean showed a significant response to application of P up to 80 kg P2O5 ha(-1) where the preceding wheat did not receive any fertilizer P. However, where wheat received 60 kg P2O5 ha(-1) the response of succeeding soybean was restricted up to 60 kg P2O5 ha(-1). It obtained the remaining P from residual fertilizer. There was a significant response of wheat to direct application of P up to 60 kg P2O5 ha(-1) but relatively little response to residual P. The differential response of the two crops is due to climatic differences between wheat and soybean growing seasons, corresponding with the differences in soil conditions such as temperature and moisture, and differences in the P-absorption abilities of the two crops. The results suggest that in soybean-wheat system of this region, a direct application of 60 kg P2O5 ha(-1) to both soybean and wheat was sufficient to meet their P needs. It also enhanced fertilizer P use efficiency and P recovery, partitioned total biomass produced to grain yield, and optimized cost effectiveness, thus reducing the potential risk of P contamination of groundwater. Both improved mosaic-resistant cultivars of soybean (SL 295 and PK 416) showed similar yield responses to fertilizer P, and comparable yield potential of similar to2.5 t ha(-1). (C) 2002 Elsevier Science B.V. All rights reserved.