Effects of rice stalks mulching combined with green manure (<italic>Astragalus smicus </italic>L.) incorporated into soil and reducing nitrogen fertilizer rate on rice yield and soil fertility

Abstract

<p id="C3">Planting green manure and straw retention is an effective measure to improve soil fertility. Two-year field experiment were conducted to assess the effects of reduced nitrogen rate under the rice straw mulching combined with planting green manure (<italic>Astragalus sinicus </italic>L.) at full bloom stage on rice yield, yield components, and soil nutrient availability in Hantai district, Hanzhong city, Shaanxi province from 2018 to 2020. Five treatments were assigned: (1) CK, winter fallow, no straw mulching, no fertilization; (2) NPK, winter fallow, no straw mulching, conventional nitrogen fertilizer rate; (3) GRN1, planting green manure in winter, rice straw mulching with conventional N fertilizer rate; (4) GRN2, planting green manure in winter, rice straw mulching with 80% conventional N rate; (5) GRN3, green manure planting in winter, rice straw mulching with 70% conventional N rate. The results showed that: (I) rice yield (Quanxiangyou 1521) of GRN1 was 10,047 kg hm^-2, which was higher 6.7% than that of NPK, and GRN2 and GRN3 had marginal effects in 2019. Moreover, the yield (Huanghuazhan) of GRN2 and GRN3 were significantly higher than that of NPK by 6.6% and 5.8% in 2020, respectively. Compared with CK and NPK, the rice straw mulching combined with planting green manure significantly enhanced the rice yield by 67.9%-83.0% and 2.8%-6.7%, respectively. (II) Planting green manure combined with rice straw mulching increased soil organic carbon content and available P content in 0-20 soil layer. Compared with NPK treatment, soil organic carbon and available P content of GRN2 increased 6.8%-13.2% and 9.9%-12.6%, respectively. Correlation analysis indicated that rice yield was significantly correlated with plant height, fresh weight per plant, fresh root stubble weight, filled grain number per panicle, and 1000-grain weight. Compared with NPK, GRN2 significantly increased effective panicle, effective grain number per panicle by 13.0%-29.3% and 4.5%-14.3%, respectively. Meanwhile, GRN2 significantly increased plant height, fresh weight per plant, and root fresh weight by 10.4%, 23.6%, and 30.0%, respectively. In conclusion, rice stalks mulching combined planting green manure with 20% reduced nitrogen rate can improve rice yield and agronomic performance, enlarge soil carbon sequestration capacity, and increase soil nutrients availability, which is a green rice cultural practice adapted to Hanzhong area.