Subsoiling with straw return promotes soil nitrogen supply and increase maize yield in saline-alkaline farmland of the Yellow River Delta

The distinct soil physicochemical properties of saline-alkali farmland often lead to nutrient deficiencies, particularly in nitrogen. Both straw return and tillage are essential practices for modifying saline-alkali soils, however, their combined effects on soil properties, nitrogen(N) transformation and absorption, as well the crop yield remain inadequately understood. A field experiment was conducted to assess the cumulative impacts of straw return and tillage (rotary tillage, deep tillage and subsoiling) on soil salinity, nitrogen transformation and maize yield. The results revealed that the soil pH and electrical conductivity (EC) significantly decreased from the 0–20 cm layer to the 20–40 cm layer, indicating that deep tillage was less effective on salt accumulation in the surface soil. The return of straw return and tillage practices significantly influenced the fractions of soil organic nitrogen (SON) and the distribution percentage in total nitrogen. Additionally, these practices notably interacted to increase soil acid insoluble-N, active SON and stable SON. The combination of straw return and rotary tillage resulted in a higher content of stable SON in the 0–20 cm soil layer. Conversely, the combination of straw return and subsoiling proved to be more effective on soil available N and active SON supplying, as well as maintaining stable nitrogen levels. Furthermore, straw return combined with subsoiling achieved the highest plant nitrogen uptake and yield, with increases of 21.7% and 38.2%, respectively, compared to the rotary without straw. Principal component analysis (PCA) revealed that stable SON was the primary contributor influencing maize yield, while inorganic N in the 0–20 cm layer and hydrolysable ammonium nitrogen (NH4+-N) in the 20–40 cm were also the closely related factors. These results provide a new insight for implementing straw return measures to enhance soil quality and increase crop production in saline-alkali farmland. © 2024 British Society of Soil Science.