Green Manuring Enhances Nitrogen Use Efficiency of Rice and Soil Nutrient Contents of Paddy Soil

Aims: To investigate the effects of green manures (GMs) combined with inorganic nitrogen (N) fertilizer on N use efficiency, and the yield of Sinn-thu-kha rice, as well as on soil nutrient contents, field experiments were conducted at the Department of Agronomy, Yezin Agricultural University from December to June during the summer and monsoon seasons of 2023 and 2024. Study Design and Methodology: The study employed a split-plot design with three replications. Different rates of inorganic N fertilizer were assigned as the main plot factor, including N0%, N25%, N50%, N75%, and N100%, based on the recommended N rate of 102 kg ha-1. GM crops served as the subplot factor, which included no GM (G0), rice bean (GRB), sunn hemp (GSH), and dahincha (GDC). GMs were cultivated and incorporated into the soil at the time of flowering, followed by rice cultivation. Results: The results indicated that the N100% yielded the highest dry matter, N uptake, N use efficiency, and rice yield. Among the GM treatments, GSH performed the best. The combination of GSH with N100% achieved the highest N use efficiency and rice yield. Similarly, GSH combined with N75% resulted in greater dry matter, higher N uptake, N use efficiency, and yields compared to GRB or GDC combined with N75%, N100%, or the inorganic N treatment alone. Over two years, soil nutrient contents such as total N (%), available phosphorus (ppm), available potassium (ppm), and organic carbon (%) all increased. Conclusion: Green manure enhances the N use efficiency of rice and improves the nutrient content of paddy soil. With either 75% or 100% of the recommended inorganic N, sunn hemp (GSH) promotes soil nutrient content, dry matter production, N uptake, N use  efficiency, and rice yield. This combination allows for a reduction of 25% in inorganic N fertilizer without compromising rice yield. Consequently, this practice can help lower fertilizer costs, reduce environmental pollution, and promote both soil health and long-term rice production.