Nutrient Uptake and Apparent Balances for Rice-Wheat Sequences. II. Phosphorus

Abstract

ABSTRACT Phosphorus (P) nutrition of the rice-wheat (RW) systems of the Indo-Gangetic Plain of South Asia has become important due to the alternate flooding and drying cycles of this crop rotation. Field experiments on the RW cropping sequence were conducted at three locations of Bangladesh on three soil types. Two fertilizer doses—farmers' practice (FP) and soil-test based (STB), containing recommended amounts of P, nitrogen (N), potassium (K), and other nutrients—were compared with mungbean or maize as a third crop. The objective of the experiments was to detect P deficiency, if any, in rice, wheat, mungbean, and maize, and to compare the FP and STB doses of fertilizers in rice-wheat-mungbean and rice-wheat-maize sequences under two mungbean management practices (residue removed or retained) and one maize management practice (residue removed) in terms of P nutrition of those crops and annual system-level P removal and apparent P balance in the soil. The apparent P balance was negative with the FP dose (−1 to −9 kg ha−1 for mungbean sequences at Joydebpur and Nashipur) and there was soil P accumulation under both the STB dose (9–49 kg ha−1) and zero N control (13–50 kg ha−1) across sites. The effect of maize or mungbean as the pre-rice crop on the apparent P balance of various RW sequences was not significant. Phosphorus deficiency occurred at all sites in wheat and maize, and at Ishwordi in rice, suggesting that P fertilizer recommendations need to be revised for RW systems in Bangladesh. The results also suggest that long-term monitoring for P concentration, uptake, and balance would be necessary for improving not only the productivity and sustainability of this system but also the fertilizer P-use efficiency.