Reducing Nitrogen, Optimizing Nitrogen Fertilizer Types and Inoculating Rhizobium Can Optimize the Distribution of Soil Water-nitrogen and Increase Yield of Soybean (Glycine max L.); [減氮，優化氮肥類型並接種根瘤菌可優化大豆(Glycine max L.)土壤水氮分布並增產]

In agricultural production, strategies such as rhizobia inoculation and nitrogen application are widely employed to enhance soybean (Glycine max L.) yield. However, research on the mechanisms of soybean yield increase and soil water and nitrogen environment by the above management methods remains unclear. Additionally, there is a lack of a comprehensive management method to consider the high yield of soybean while minimizing the nitrogen surplus of soybean soil. In this study, a series of 14 treatments were implemented over a two-year span of field experiments. These treatments encompassed three levels of nitrogen application (N0: 0 kg N ha‒1, N1: 90 kg N ha‒1, N2: 180 kg N ha‒1), rhizobium inoculation (R: rhizobium-inoculated seeds, W: pre-sowing water dressing), and three nitrogen types (U: urea, S: slow-release nitrogen fertilizer, SU: a blend of U and S, U/S = 4/6). The aim was to assess the effects of each treatment on soybean growth, physiological indices, seed yield, as well as economic and environmental outcomes over a two-year period. The findings revealed that rhizobium inoculation, reduced nitrogen fertilizer application, and the utilization of a mixture of urea and slow-release nitrogen fertilizer (SURN1) led to varying degrees of enhancement in soybean growth, seed yield, and net income. Over the two-year span, R demonstrated an average increase of 5.9% compared to W. Furthermore, N1 exhibited yield improvements of 18.0% to 49.9% and net profit increases of 52.7% to 70.1% when compared to N0 and N2. The SU treatment exhibited enhanced soybean growth at each developmental stage and achieved the highest seed yield increase of 5.8% to 14.1%. Concurrently, the R, SU, and N1 treatments increased water consumption during soybean growth, enhanced water-nitrogen utilization efficiency, and diminished nitrate nitrogen residue in the soil. In summary, combining rhizobia inoculation with the application of urea mixed slow-release fertilizer (SURN1) under reduced nitrogen conditions optimizes water and nitrogen utilization efficiency, maximizes net income from seed yield, and yields relatively favorable environmental outcomes. This integrated approach holds promise in addressing future climate fluctuations and ensuring regional food security. © (2023), (Taiwan Joint Irrigation Associations). All rights reserved.