Co-incorporation of Chinese milk vetch and chemical fertilizers ameliorates chlorophyll content, nitrogen uptake and soil property favouring rice quality

The objective of this study was to assess the impact of the time and rate of co-incorporation of Chinese milk vetch (CMV) with chemical fertilizers on rice quality and associated factors in South China. Here, a pot experiment with an orthogonal design L₉ (3³) was conducted to study the effect of the co-incorporation practices on rice quality, leaf chlorophyll, nutrient uptake and soil property. Results showed that co-incorporation of CMV (5288 kg dry CMV ha^{- 1}) with chemical fertilizers (108 kg nitrogen (N) ha^{- 1}, 23 kg phosphorus (P) ha^{- 1}, and 89 kg potassium (K) ha^{- 1}) on 7 day before the early rice transplanting (T₄) increased methionine and lysine contents by 29.2% and 46.4%, and increased starch and amylopectin by 10.3% and 11.6% compared with those at the conventional level of chemical fertilizer input (137 kg N ha^{- 1}, 30 kg P ha^{- 1}, and 56 kg K ha^{- 1}) (T₀), respectively (P < 0.05). This was likely attributed to interactions among leaf chlorophyll, N uptake and soil property. The statistical analyses indicated that grain N content, the transport coefficient for N, leaf chlorophyll, soil organic matter, pH, the relative abundances of Actinobacteriota, Patescibacteria, and Rozellomycota were significantly correlated with quality traits of rice grain (P < 0.05). Overall, the T₄ treatment can modulate leaf chlorophyll, N uptake, soil chemical and microbial properties, and further improve amino acid, starch compositions and contents of rice grain.