Effects of Chinese Milk Vetch Incorporation and Chemical Fertilizer Reduction on Nutrient Absorption and Transport in Rice

In order to clarify the Chinese milk vetch (Astragalus sinicus L.) incorporation amount in the Chinese milk vetch-rice rotation model and screen out efficient and low-carbon fertilization methods in the southern Henan rice region, six treatments were set up, namely, the non-fertilization control (CK), conventional fertilization (F₁₀₀), and treatments with Chinese milk vetch incorporation amounts of 22.5 t/hm², 30.0 t/hm², 37.5 t/hm² and 45.0 t/hm² under 40% nitrogen fertilizer reduction (designated as G_1.5F₆₀, G₂F₆₀, G_2.5F₆₀ and G₃F₆₀ in sequence). The rice biomass, rice above-ground dry matter accumulation, transport of nitrogen,phosphorus and potassium and nutrient use efficiency at different stages were analyzed. The results showed that compared with the F₁₀₀ treatment, the nitrogen accumulation in the above-ground parts of chemical fertilizer reduction treatments significantly increased by 52.43%~124.16% and 48.11%~83.03% at the heading stage and maturity stage, respectively. Among them, the nitrogen accumulation in straw significantly increased by 58.69%~144.34% and 84.40%~160.65% respectively. The nitrogen accumulation of grains at the maturity stage increased significantly by 28.25% to 46.96%. The phosphorus absorption of straw at the maturity stage significantly increased by 72.08% to 157.47%. Compared with F₁₀₀ treatment, G_2.5F₆₀ and G₃F₆₀ significantly increased the potassium absorption of rice straw at the heading stage and the maturity stage, with the increase of 31.45%,52.61%, 30.00% and 36.42% respectively. Compared with the F₁₀₀ treatment, the nitrogen and phosphorus transport capacity of rice in the G₃F₆₀ treatment increased significantly by 206.40% and 113.78% respectively. The contribution rate of phosphorus to rice transport increased significantly by 82.11 percentage points. The agronomic utilization efficiency of nitrogen, phosphorus and potassium in the G₃F₆₀ treatment was significantly lower than that in the F₁₀₀ treatment, with the decrease of 49.39%,55.76% and 42.44% respectively. The nitrogen recovery rate of each treatment with reduced chemical fertilizer application of Chinese milk vetch increased significantly, with an increase rate ranging from 40.00 to 62.22 percentage points. The potassium recovery and utilization rate of each treatment with G_2.5F₆₀ and G₃F₆₀ increased significantly, with the increase of 43.19 and 43.89 percentage points. Correlation analysis revealed that rice yield had positive correlations with nitrogen, phosphorus, and potassium absorption at each growth stage (r=0.290~0.847^*), and had negative correlations with the transfer capacity of nitrogen and potassium at the maturity stage (r=-0.067, -0.975^**). Comprehensively considering factors such as yield, nutrient absorption and fertilizer utilization rate, the treatment of Chinese milk vetch with application of 37.5 t/hm² can promote the nutrient absorption of nitrogen, phosphorus and potassium in rice compared with the F₁₀₀ treatment, maintain a comparable nutrient transfer capacity to conventional fertilization, and increase the above-ground absorption of nitrogen, phosphorus and potassium during the vegetative growth period, thereby achieving high and stable rice yield.