Optimizing root architecture with nitrogen fertilization to improve nitrogen accumulation and yield in soybean

Xinjiang is a high-yielding region for soybean in China, but issues such as low nitrogen use efficiency limit yield. Optimizing nitrogen fertilization strategies can effectively alleviate these problems.

A two-year field experiment was conducted during the 2022 and 2023 growing seasons using a split-plot design. Two soybean cultivars, the low-yielding Xindadou 27 and the high-yielding Xinnongdou 2, were planted in the main plots. Four nitrogen application rates were applied in the subplots: 0, 120, 180, and 240 kg ha^-1.

The application of 180 kg ha^-1 nitrogen significantly increased root dry weight density, length density, and surface area density in the 0-60 cm soil layer, mainly through increases in the 0-20 cm soil layer. This treatment also enhanced the activities of key nitrogen metabolism enzymes (NR and GS/GOGAT) in roots, promoting nitrogen uptake and translocation to shoots, which increased both yield and shoot nitrogen accumulation. The higher accumulation rate and longer duration under the 180 kg N ha^-1 application rate resulted in the highest root nitrogen accumulation. In contrast, a nitrogen application rate of 240 kg N ha^-1 inhibited root growth, disrupted root nitrogen metabolism, and reduced root nitrogen accumulation. Structural equation modeling confirmed that root growth parameters have a positive influence on root nitrogen accumulation.

This study demonstrates that application of 180 kg N ha^-1 at the beginning pod stage promotes root development, improves NUE and yield for spring soybean in Xinjiang. It is recommended as a sustainable high-yield practice for the region.