Long-term straw incorporation improves nutrient accumulation in wheat seedlings by changing the soil’s hydrothermal environment to promote root growth

Crop straw incorporation plays an important role in improving soil environment, increasing crop yields and developing green and sustainable agriculture. However, the effects of long-term straw return on soil’s hydrothermal environment and the growth of wheat seedlings have not been well explored. Based on a 13-year long-term stationary experiment of straw returning to the field (2008–2021), this study investigated four straw management practices—no straw return (CK), wheat straw return (W1M0), maize straw return (W0M1), and the return of both wheat and maize straws (W1M1)—on the soil water content and temperature of lime concretion black soil, root structure, nitrogen uptake, and the quality of wheat seedlings. The results showed that straw returning treatment significantly increased soil water content at the three-leaf and four-leaf stages, but had no significant effect on soil temperature. Compared with the CK, soil water content at the three-leaf and four-leaf stages increased by 13.14%–24.67% and 7.42%–17.82%, respectively. Meanwhile, straw returning also promoted the increase of root activity at the three-leaf and six-leaf stages, at the three-leaf stage, W1M0, W1M1, and W0M1 were significantly higher than CK by 148.64%, 111.11% and 148.64%, respectively. In addition, long-term straw incorporation also promotes an increase in the nitrogen content and nitrogen accumulation of wheat seedling plants. Compared with CK, the phosphorus content of W1M0 and W1M1 treatments was higher than that of CK, while that of W0M1 treatment was lower than that of CK. The SEM model shows that soil moisture and temperature have a significant negative impact on wheat root physiology indicators (root activity and root active absorption area), while root physiology significantly indicators affects root morphology, which in turn exerts a significant negative influence on the nitrogen and phosphorus contents of above-ground plant parts. In conclusion, long-term straw incorporation is conducive to creating a soil hydrothermal environment that is suitable for the growth of wheat seedlings, thereby promoting the formation of strong wheat seedlings. In this study, the wheat straw return (W1M0) performed the best.