Search

Milk vetch (Astragalus sinicus L.; MV) is the most common winter green manure used in rice cropping systems in southern China. The utilization of MV can achieve the dual goals of soil fertilization and increased rice yield. Two long-term field experiments were conducted in Yujiang and Gaoan in Jiangxi Province, a typical double-rice cropping area, to explore the effects of 80 % conventional fertilizer for early rice supplemented with 15.0 (G1F80), 22.5 (G2F80), 30.0 (G3F80), and 37.5 (G4F80) t ha−1 MV on rice yield, soil fertility, nutrient uptake, and nutrient use efficiency. The results showed that, the yield data obtained from the 5-year (Gaoan) and 12-year (Yujiang) long-term experiments demonstrated that compared with conventional fertilization (F100), treatments with MV markedly increased the yield of early and late rice by 2.5–8.8 % and 5.6–10.9 %, respectively, and high rates of MV (G3F80 and G4F80) performed better in grain yields. The nitrogen (N) and potassium (K) uptake of early rice in Gaoan increased by 38.1 and 34.8 kg ha−1, respectively, and the N uptake of late rice in Gaoan and Yujiang increased by 11.7 and 62.6 kg ha−1 in G2F80, respectively, compared to that in F100. Compared with F100, treatments with MV significantly increased phosphorus (P) fertilizer recovery efficiency by 23.1–36.4 %, and the agronomic efficiency of N, P, and K fertilizers increased by 16.1–21.1 %, 13.9–19.6 %, and 15.7–21.4 %, respectively. Partial least squares path model analysis indicated that soil available P was the most important factor affecting the nutrient uptake of rice, and available K was the most important factor affecting fertilizer use efficiency. Our results suggested that 22.5 t ha−1 MV supplemented with 80 % chemical fertilizer is recommended for double-rice cropping sites to improve rice yield and crop uptake and the use efficiency of N, P, and K fertilizers. • Green manure with 80 % of N, P, and K fertilizer increased or maintained the multi-year yield. • Green manure with 80 % of N, P, and K fertilizer enhanced the grain N, P, and K uptake. • Green manuring increased the use efficiencies of N, P, and K fertilizer. • Application of 22.5 t ha−1 milk vetch with 80 % of chemical fertilizer can be recommended for double-rice cropping sites. [ABSTRACT FROM AUTHOR]

Green manuring is a potential method for reducing chemical N fertilizer input and reactive N losses to the environment that can achieve dual goals of food security and green development of agriculture. In this study, three long-term field experiments in south China and process-based model (WHCNS_LIXIM model) were combined to examine effects of long-term green manure substitution on soil N supply, crop N uptake, and N losses in rice production system. Results showed that green manure substitution significantly improves soil mineral N by 27.4–94.9% and 1.0–45.0% at jointing and maturity stages, respectively, compared with the use of chemical N alone. Moreover, 18.4–62.2% of crop N uptake increased at the maturity stage at Xinyang and Yujiang sites. The model demonstrated satisfactory performance in modeling dynamics of soil mineral N, crop N uptake, crop dry matter, and grain yield of the rice–green manure system with a determination coefficient (R2) > 0.967 and slope of linear regression equation (β) close to 1.0. Simulated N budgets presented that green manure reduces 20–40% of the chemical N fertilizer input and decreased 5.5%, 25.1%, and 30.6% of N losses by ammonia volatilization, leaching, and runoff, respectively, when green manure application rates (fresh matter) are less than 30 t ha−1. However, the total N loss increased with the increase of green manure application amounts when application amounts are larger than 30 t ha−1. These findings indicated that the further reduction of chemical N fertilizer was needed when the application amount of milk vetch was higher than 30 t ha−1. A milk vetch application of 15–30 t ha−1 was recommended to substitute 20–40% of chemical N fertilizer to improve crop N uptake and reduce N losses, and develop green rice production system in the study areas. • Long-term green manure substitution significantly improves soil mineral N. • Long-term green manure substitution enhances crop N uptake and reduces N losses. • The WHCNS_LIXIM model performed well in simulating soil mineral N and crop N uptake. • Milk vetch application of 15–30 t ha−1 was recommended to improve crop N uptake and reduce N losses. [ABSTRACT FROM AUTHOR]