Comparison of phosphorus application on crop yield and soil phosphorus pool in rapeseed/wheat-rice rotations: An 8-year field experiment

Context: Globally, the limited capacity of soil phosphorus (P) supply is one of the significant factors constraining crop yield. In paddy-upland rotation systems, the alternation of dry and wet conditions and the rotation of different crop types result in various responses to P application. However, the impacts on rice growth and soil P responses for different upland crops have been insufficiently examined. Objective: The objective of this study was to evaluate the effects of long-term P fertilization on soil P availability and rice yield in rapeseed-rice (RR) and wheat-rice (WR) rotation systems in the Yangtze River Basin of China. Furthermore, the study aimed to carry out soil P fractions to evaluate the specific fraction that contributes to the available P pool and subsequently the yield of rice. Methods: Field experiments were conducted over an 8-year period (2015-2023) to examine the impact of three P treatments (i.e., P0: no P; P60: 60 kg P2O5 ha-1; P120: 120 kg P2O5 ha-1) on crop yield, P uptake, soil Olsen-P and soil Pi Pool in RR and WR rotation systems. Results: The results showed that P application significantly increased crop yield. Compared to the P0 treatment, on average, the P60 and P120 treatments increased rapeseed yield by 305.4 % and 460.2 %, respectively, and wheat yield by 76.8 % and 129.3 %, respectively. The rice yield increased by 46.3-48.3 % and 51.3-54.5 % in the RR and WR rotation, respectively. Under three P fertilizer treatments, rice yield and P uptake in the RR rotation were higher than in the WR rotation, with an average increase of 5.2 % and 14.7 %, respectively. The soil Olsen-P increased by 49.0-146.4 % and 288.3-530.2 % in the P60 and P120 treatments, when compared to the initial value, respectively. In the P120 treatment, the Olsen-P content in the RR rotation increased by 17.3 % (upland) and 15.6 % (paddy) compared to the WR rotation. The Hedley-Pi fraction indicated that P fertilizer application significantly increased the contents of NaHCO3-Pi and NaOH-Pi. The relative important analysis and correlation analysis showed that NaOH-Pi contributed significantly to increasing crop P uptake. Conclusions: The P fertilizer application not only enhanced crop yield but also contributed to establishing a soil P pool. The rice yield and P uptake were higher in the RR rotation than in the WR rotation, and the rate of Olsen-P accumulation in the RR rotation was faster than that of the WR rotation. Notably, the rapeseed season facilitated greater NaOH-Pi accumulation than Wheat season for subsequent rice absorption and utilization. Implications: The research outcomes provided insights into P fertilizer management and cropping system strategies in paddy-upland rotation systems.