Effects of conservation tillage methods on maize growth and yields in a typical black soil region

Implementation of conservation tillage is crucial for protecting black soil in Northeast China and ensuring national food security. A three-year field experiment was conducted to examine the impact of conservation tillage on maize yields and its key factors in a typical black soil region of Northeast China. Four treatments were designed, including conventional ridge tillage without straw mulching (CK), no-tillage with 100% crushed straw mulching (T1), no-tillage with high stubble and 100% straw mulching (T2), and reduced tillage with 100% straw strip mulching (T3). This study analyzed the physical and chemical properties of soil, maize growth, yields, and its components to assess the effects of different treatments on soil and maize yields. The results demonstrated that conservation tillage treatments (T1, T2, and T3) increased soil organic matter content in the 0–20 cm soil layer compared with the CK treatment. Additionally, conservation tillage significantly improved the soil water content during the sowing to seedling stages, while decreasing the soil temperature. T1, T2, and T3 treatments led to increases in the soil water content, ranging from 7.8% to 30.4%, 9.0% to 18.7%, and 17.3% to 20.0%, respectively. Meanwhile, the soil temperature decreased by 2.56 °C to 3.11 °C, 2.02 °C to 2.27 °C, and 0.94 °C to 1.93 °C, respectively. The data revealed that the emergence times of T1 and T2 were delayed by 5–7 days and 4–6 days, respectively. However, T3 only experienced a delay of two days. Over the three years, the average seedling emergence rate of T3 treatment increased by 3.2% compared to CK, whereas the emergence rates of T1 and T2 decreased by 4.3% and 4.7%, respectively. T1, T2, and T3 treatments reduced the uniformity of plant height and dry matter accumulation at the sixth leaf collar stage, with T3 treatment exhibiting a significantly smaller decrease than the T1 and T2 treatments. Additionally, dry matter accumulation after the sixth leaf collar gradually decreased in T3 compared to that in the other treatments. T1 and T2 significantly reduced the yield by 7.5% to 15.6% and 5.5% to 12.9%, respectively, over the course of three years. However, T3 treatment did not show a significant difference compared with CK. The structural equation model (SEM) indicated that conservation tillage indirectly affected yields by regulating soil water content and temperature, thereby influencing emergence time, emergence rate, ear number, and 100-kernal weight. Furthermore, conservation tillage can directly affect emergence quality and yield components, subsequently affecting yields. Therefore, T3 is an optimal conservation tillage practice for a typical black soil region of Northeast China. T3 not only improves soil organic matter content but also helps in adjusting the contradiction between soil moisture and temperature to shorten the emergence time, improve the quality of emergence, and stabilize yields.