Purpose

A 6-year (2011–2016) field experiment was performed to explore the effects of partial substitution of chemical fertilizer by green manure on rice yield, sustainability yield index, and the building-up of different fractions of soil organic carbon, soil nitrogen, and phosphorus.

Materials and methods

The experiment included no fertilization (NF), chemical fertilizer only (CF₁₀₀), and Chinese milk vetch (Astragalus sinicus L.) incorporation with 80%, 60%, 40%, 20%, and 0% of total N, P, and K supplied from chemical fertilizer (MVCF₈₀, MVCF₆₀, MVCF₄₀, MVCF₂₀, and MVCF₀, respectively) treatments. The soil organic carbon fractions, soil nitrogen, and phosphorus fraction contents were measured over 6 years.

Results and discussion

In comparison with CF₁₀₀ treatment, the MVCF₈₀, MVCF₆₀, and MVCF₄₀ treatments significantly increased rice yield between 2013 and 2016, thus improving sustainability yield index. The soil organic carbon fractions increased 15–58%, 16–61%, 14–50%, and 12–33% in the MVCF₈₀, MVCF₆₀, MVCF₄₀, and MVCF₂₀ treatments, respectively, compared with the CF₁₀₀ treatment (p < 0.05). The easily oxidizable nitrogen, acid hydrolysable pool II nitrogen, total nitrogen, NaOH extractable phosphorus, HCl extractable phosphorus, and total phosphorus contents in the MVCF₄₀ treatment were 17%, 28%, 9%, 12%, 15%, and 8% higher than those in the CF₁₀₀ treatment (p < 0.05). The MVCF₆₀ and MVCF₈₀ treatments further increased the contents of these nitrogen and phosphorus fractions compared with the CF₁₀₀ treatment. Stepwise multiple linear regression analysis showed that the average yield was positively influenced by the contents of total phosphorus, easily oxidizable nitrogen, and dissolved organic nitrogen, and that the sustainability yield index was positively influenced by the contents of easily oxidizable carbon and total organic carbon.

Conclusions

Chinese milk vetch incorporation with a 20–40% reduction in chemical fertilizer inputs may be a potential fertilization practice for improving rice productivity and sustainability.