Effects of Lupine Return and Nitrogen Fertilizer on Rice Yield, Nitrogen Use Efficiency and Soil Fertility

The rice was used as the experimental material to conduct a 2-year field experiment. Two treatments including lupine return amount (M) and nitrogen application amount (N) were set up. Two levels of lupine application were set at 0 kg/hm² and 18 t/hm² for M treatment, and six levels of nitrogen fertilizer application were set at 0 kg/hm², 90 kg/hm², 135 kg/hm², 180 kg/hm², 225 kg/hm² and 270 kg/hm² for N treatment, The effects of lupine application and nitrogen fertilizer application on rice yield, nitrogen fertilizer utilization rate and soil physical and chemical properties were studied. The results showed that after lupine application, the effective panicles per plant, total grains per panicle and 1000-grain weight of rice all increased. The rice yield of treatment (MN₁₃₅) with 135 kg/hm² nitrogen fertilizer application combined with lupine return application 18 t/hm² was significantly higher than that of other treatments, increasing by 25.6% to 34.0% compared with the MN0(CK₂) treatment. Lupine application could increase soil pH and soil organic matter content. The contents of available nitrogen, available potassium and organic matter in the MN₁₃₅ treatment were the highest among all treatments, increasing by 35.4% to 90.2%, 31.4% to 39.1% and 10.6% to 15.0% respectively compared with the CK₂ treatment. Considering all factors, the combination of 18 t/hm² lupine return application and 135 kg/hm² chemical nitrogen fertilizer application was the optimal combination, which could be recommended as a fertilization model for sustainable and stable high-yield rice production and soil nutrient improvement.