Objective The dry-farming soil of the Loess Plateau is characterized by poor structure and weak water and nutrient retention capacity. The application of exogenous organic and inorganic substances is a key technology for improving soil quality and increasing crop yield in this area. This study explored the synergistic effects of the combined application of bentonite and straw on enhancing soil structure, water and nutrient retention capacity, and crop yields in oat fields within this region.

Methods  A long-term field experiment was established in 2019 in the dryland farming region of the Loess Plateau in Inner Mongolia. It comprised four treatments: no bentonite or straw application (CK), bentonite application alone (OB), straw application alone (OS), and combined application of bentonite and straw (H). Soil samples were collected from the soil profile after oat harvest in 2023 to determine soil aggregate composition, bulk density, porosity, available nutrient content, soil water storage, and crop yield and its components. Correlation and principal component analyses were conducted to identify the factors influencing yield.

Results Compared with CK, the other three treatments significantly improved the soil structure, water and nutrient retention capacity, and oat yield, with the following order of effectiveness: H>OS>OB (P<0.05). The H treatment significantly increased the content of>2 mm and 0.25−2 mm macroaggregates by 33.02% and 37.78%, respectively, reduced bulk density by 6.43%, and increased porosity by 7.86%. The improvement effect extended to the 20−40 cm soil layer. At the same time, the contents of alkali-hydrolyzable nitrogen, available potassium, and available phosphorus were significantly increased by 6.89%, 17.28%, and 30.82%, respectively. The H treatment exhibited the highest water-use efficiency and rainfall-use efficiency, increasing them by 36.84% and 35.25%, respectively, compared with CK, both at a significant level. The number of effective panicles, grains per panicle, 1,000-grain weight, biological yield, and grain yield were all significantly higher than those of the control. The increase in biological yield ranged from 9.68% to 34.42%. Correlation and principal component analysis showed that yield was significantly positively correlated with>2 mm and 0.25−2 mm aggregate content, aggregate stability, and nutrient content, with alkaline nitrogen and 0.25−2 mm aggregate as the main positive influencing factors.

Conclusions  In dryland oat fields on the Loess Plateau, a one-time basal application of bentonite (18000 kg/hm²) combined with annual straw incorporation (6000 kg/hm²) can synergistically enhance the content of macroaggregates in the 0−40 cm soil layer, improve soil structural stability, reduce bulk density in deeper soil layers, increase porosity, and significantly elevate soil available nutrient content and soil water storage. This ultimately increases oat yields and water-use efficiency, achieving a synergistic effect of soil structure improvement, enhanced water and nutrient retention capacity, and increased oat yields. This approach can serve as an effective technical pathway for enhancing regional farmland productivity and resource-use efficiency.