Objectives Milk vetch (Mv) is rich in nitrogen, so it is an important source of organic N. The effects of nitrogen reduction on rice yield, nitrogen uptake, nitrogen use efficiency and soil organic matter composition under incorporation of milk vetch (Astragalus sinicus) were studied based on two two-year field experiments. This study evaluated the effects of different N application rates combined with milk vetch incorporation in a rice paddy.
Methods Field experiments were conducted in Guichi and Huoshan cities, Anhui Province, from 2018–2019. No N fertilizer (–N) and conventional N application rate (100%N) under winter fallow were set as control treatments, and Mv returning to field combined with 0% (Mv), 40% (Mv+40%N), 60% (Mv+60%N), 80% (Mv+80%N) and 100% (Mv+100%N) of conventional N application rate were set up as treatments. After rice harvest in 2018 and 2019, the yield and nitrogen uptake of rice were investigated, and soil carbon and N contents were analyzed.
Results Mv+60%N elicited the highest rice yield in both years and two sites (averaged 8349 kg/hm2), which were not significantly different from those of Mv+80%N, Mv+100%N and 100%N treatments, but significantly higher than those of Mv+40%N and Mv. Compared with 100%N, Mv+40%N, Mv+60%N, Mv+80%N and Mv+100%N treatments increased N fertilizer utilization rate by 46.3%, 31.6%, 16.1% and 4.4%, respectively, and increased the agronomic efficiency of nitrogen fertilizer by 61.6%, 43.6%, 23.2% and 0.1%, respectively. After milk vetch returning in 2018 and 2019, the soil organic carbon and particulate organic carbon were increased by 3.3%–13.8% and 14.9%–32.0%, respectively.
Conclusions The combination of milk vetch incorporation with 60% of conventional chemical N fertilizer input meets the N nutrition requirement of rice, maintains a high yield, increases the nitrogen use efficiency, and agronomic efficiency by 31.6% and 43.6%, respectively, Hence, the Mv+60%N is considered as the optimum fertilization mode in paddy fields in Anhui.
DownLoad: