Phosphorus application and straw incorporation increase yield and phosphorus utilization in a rape-rice rotation system

Objectives We assessed the appropriate combination of straw incorporation and phosphorus application for the efficient production and phosphorus utilization in a rape-rice rotation system.

Methods Field experiment was conducted for two years in Mianyang, Sichuan Province, under the rape-rice rotation system. The treatments were: P application with straw returning (T2) and without straw returning (T1), no P application in both rape–rice seasons (P1), application of 120 kg/hm² P₂O₅ on rape and 90 kg/hm² P₂O₅ on rice (P2), application of 120 kg/hm² P₂O₅ only on rape (P3), and application of 90 kg/hm² P₂O₅ only on rice (P4). At heading and maturing stage of rape and rice, plant samples were collected for the analysis of dry matter accumulation (DM), yield and P content.

Results Among the four treatments, P3 recorded the highest yield, DM and P uptake of rape, two rice cultivars and the rotation system. Compared with P2, P3 increased the yield, DM, post-flowering dry matter transfer and P uptake of rape and rice in two seasons by 10.14%–27.65%, 8.39%–9.71%, and 1.86%–5.65% respectively. Compared with the P2 treatment, P4 treatment increased the DM, post-flowering transport amount and yield of rice, but decreased the DM of rape and P absorption and the rotation system. Compared with P2, P3 increased the apparent P fertilizer efficiency of the system by 92.70%, while P4 did not exhibit significantly higher P efficiency. Under the same P treatment, straw returning improved the yield, DM and P uptake of rape, rice and rotation system and increased the translocation of DM and P accumulated before flowering stage of rape and rice than T1.

Conclusions In rape-rice rotation system, applying P on rape could satisfy the P nutrition for rape season, the P returned to field by rape straw could be absorbed and used more efficiently by the following rice than P fertilizer, thereby increasing the P use efficiency, dry matter production and translocation, and yield of the rotation system. On the contrary, application of P only in rice season, no matter rice straw returning to field or not, does not provide enough P for rape, and decreases the yield and P efficiency of the system. Therefore, application of P on rape combined with straw incorporation is the best P application mode.