How to improve the light-simplified and cleaner production of rice in cold rice areas from the perspective of fertilization

Side-deep fertilization could achieve cleaner and light-simplified production of rice by reducing fertilizer use, improving fertilizer utilization, and alleviating labor shortage. However, little is known about the agronomic and environmental benefits of side-deep fertilization technology and the operational scale of farmers targeted by the government for suitable promotion and subsidization of side-deep fertilization technology in cold rice areas. To address this, a two-year field experiment was designed in the Heilongjiang province that included five treatments to the rice: a control without fertilizer (CK), broadcasting urea (NPK), broadcasting urea under 10% N reduction (CSA), under 15% N reduction, applying controlled-release urea by side-deep fertilization without topdressing (DFA) and a topdressing of 20% urea in the later stage (DTA). The results showed that compared with NPK, DFA and DTA significantly improved nitrogen use efficiency (NUE) by 32.4%–43.0%, and DTA sustained grain yield. However, CSA reduced grain yield and NUE compared with other fertilized treatments. The NH3 emissions under CSA, DFA and DTA were markedly lower by 7.58%–20.8% than that in the NPK treatment (P < 0.05). In all, the nitrogen surplus under DFA, DTA and CSA were 20.3%, 71.9% and 41.9% lower than that under NPK, respectively. For economic profit, CSA and DFA led to a reduce of 43.1% and 2.09% compared with NPK mainly due to the decrease in yield, while DTA did not change markedly. Therefore, side-deep fertilization had better agronomic and environmental benefits in cold rice area. Moreover, only operational scale of famers above 7.68 or 15.4 ha could achieve cost recovery when side-deep fertilization machinery worked for 10 or 5 years. However, the survey data showed that the average operational scale of the farmers in cold rice areas is 14.6 ha, and 46.5% of the farmers had an operational scale of more than 7.68 ha. Therefore, there was a great potential for the promotion of side-deep fertilization technology in cold rice areas. It is suggested that the government should make farmers with an operational scale of 7.68 ha or more a priority target for promotion and subsidy in order to better realize the promotion and application of the technology.