Improved crop yield and phosphorus uptake through the optimization of phosphorus fertilizer rates in an oilseed rape-rice cropping system

The oilseed rape-rice cropping system is one of the predominant types of paddy-upland cropping systems in East Asia. An optimal phosphorus (P) fertilization strategy is need to enhance the crop yield and the apparent P recovery efficiency (APRE) in the paddy-upland cropping systems. A 2-year field experiment under the oilseed rape-rice cropping system with contrasting P fertilization treatments (0, 45, 90, 135, and 180 kg P2O5 ha−1) was conducted in the middle Yangtze River Basin, central China. The crop yield, P uptake, and soil P bioavailability were analyzed. The results demonstrated that P fertilization promoted crop growth; it significantly improved crop yield and shoot P uptake, with enhancements of 185.6–238.9% and 202.7–822.1%, and 5.6–12.2% and 16.4–34.0% for oilseed rape and rice, respectively. The number of pods and panicles per plant was the most strongly affected component of oilseed rape and rice under contrasting P conditions. The best-recommended rates of P fertilizer for optimal seed yield were 57.0 and 41.5 kg P2O5 ha−1 for oilseed rape and rice, respectively. Excessive P fertilization reduced the P harvest index (PHI) and APRE. When the annual P fertilizer input was 90 kg P2O5 ha−1, the apparent P balance (APB) was neutral. P application mainly increased the content and proportion of the labile inorganic P (Pi) pool and the moderately labile Pi pool. Among the multiple soil Pi fractions, the effects of P inputs on the P uptake of oilseed rape and rice were best explained by NaHCO3-Pi and NaOH-Pi, respectively. The effective use of soil moderately labile Pi during the rice season reduced the demand for P fertilizer. In conclusion, the oilseed rape-rice cropping system requires the addition of exogenous P fertilizer to achieve a high yield; the optimal P fertilizer management strategy should emphasize P fertilizer input in the upland season based on balanced fertilization.