Effects of long-term incorporation of milk vetch combined with reduction of chemical fertilizer on yield, quality and soil fertility of early rice in Jiangxi

  Objectives  This study was conducted to evaluate the effects of incorporating different amounts of milk vetch combined with reduced chemical fertilizer on early rice yield and rice quality in a double rice cropping system in South China, in order to provide a theoretical basis for chemical fertilizer reduction and high-quality rice production in the region.

  Methods  The 12-years long-term experiment located at Yujiang District of Yingtan City, Jiangxi Province was established in 2008. The seven treatments included winter fallow with no fertilization (CK), winter planting of milk vetch with no fertilization (MV), winter fallow with 100% chemical fertilization (F₁₀₀, conventional fertilization), 15000 kg/hm² milk vetch + 80% chemical fertilizer (G₁F₈₀), 22500 kg/hm² milk vetch + 80% chemical fertilizer (G_1.5F₈₀), 30000 kg/hm² milk vetch + 80% chemical fertilizer (G₂F₈₀), 37500 kg/hm² milk vetch + 80% chemical fertilizer (G_2.5F₈₀). The effects of milk vetch rate on rice yield, yield components, appearance quality, starch content, protein content, fat content and amino acid composition were analyzed.

  Results  Under the condition of 20% reduction of chemical fertilizer, different incorporation rate of milk vetch increased rice yield and the effective panicle. Compared with conventional fertilization treatment, the average yields in G₂F₈₀ and G_2.5F₈₀ treatments were increased by 6.3% and 8.0%, respectively. The yield of G_2.5F₈₀ treatment reached 7.17 t/hm², and the effective panicle was significantly increased by 7.4%, compared with F₁₀₀. Rate of milk vetch incorporation influenced the physico-chemical properties of soil. G₂F₈₀ significantly increased soil organic matter by 13.1% and total nitrogen by 12.8% while maintaining soil available nutrient content, compared with F₁₀₀ treatment. Low incorporation rate of milk vetch under reduced fertilizer conditions equally reduced the appearance, palatability of rice. However, there was no significant difference in the appearance quality and cooking and eating quality of rice treated with between G_2.5F₈₀ and F₁₀₀ treatments. Compared with F₁₀₀ treatment, the protein content and total amino acid content in G_2.5F₈₀ treatment increased by 19.1% and 59.4%, respectively, and the essential amino acid content in MV treatment increased by 49.8%. The lysine and isoleucine contents of G_1.5F₈₀ treatment were the highest, with 147.6% and 145.7% increases compared to F₁₀₀ treatment.

  Conclusions  Incorporation of milk vetch under reduced chemical fertilizer application effectively improved soil fertility, thereby improving rice yield and nutritional quality. However, low incorporation rate would decrease the appearance and palatability quality of rice to some extent. Incorporation of 37500 kg/hm² milk vetch combined with 80% chemical fertilizer elicited superior agronomic performance and nutritional quality.