[Impacts of one-off fertilization on nitrogen leaching and economic benefits for rice-rape rotation system]

One-off fertilization is a new technology of one-time applying base fertilizer near the rhizosphere during whole crop cultivation period. It has the advantages of simplifying fertilization manage-ment and reducing labor costs, but its impacts on environment, such as leaching characteristics need further analysis. We set five treatments in the typical rice-rape rotation system in the middle and lower reaches of the Yangtze River, including control treatment (CK), farmers' practice treatment (FP), optimal fertilizer treatment (OPT), one-off application of urea fertilizer treatment (UA) and one-off application of controlled release urea treatment (CRF). Using in situ leaching monitoring method, nitrogen (N) leaching characteristics at 90 cm depth of soil in rice-rape rotation system under different treatments were obtained, the impacts of one-off fertilization on N lea-ching were evaluated and its economic benefits were comprehensively analyzed. The results showed that the main forms of N in leachate were different for rape and rice. In the rape season, NO₃^--N was the major component of leachate, while for rice season NO₃^--N and NH₄⁺-N were equally important. In the whole rotation period, the inorganic N leaching mainly occurred in the rice season, and compared with FP, OPT and UA, the total amount of inorganic N leached by CRF were significantly reduced by 33.7%, 20.8%, and 20.7%, respectively. However, the effects of different fertilization treatments on N leaching in rape season were not significantly different. Under the same N application rates, compared with OPT, UA ensured the stable yield of rape and rice and significantly increased the NAE in rape season by 15.1%, but failed to improve the NAE in rice season. There was no significant difference between OPT and CRF in rice yield and NAE, but rape yield and NAE of CRF significantly increased by 10.7% and 18.9%, respectively. From the economic front, compared with OPT, UA and CRFincreased rapeseed income by 3660 and 3048 yuan·hm^-2, and rice income by 3162 and 2220 yuan·hm^-2. Therefore, considering the effects of various fertilizer treatments on N leaching, crop yield, and economic benefits, one-off base fertilization application of controlled release fertilizer technology could ensure stable or increase crop yields, and improve farmers' income, while significantly reduce the inorganic N leaching loss. Such technology is recommended for future rice-rape rotation cultivation.