Integrated Moldboard Ploughing and Organic–Inorganic Fertilization Enhances Maize Yield and Soil Fertility in a Semi-Arid Region of North China

To address soil degradation from long-term monoculture, rotary tillage, and excessive chemical fertilization in semi-arid regions of China, we conducted a three-year field experiment. We assessed the synergy of integrated management practices combined with both continuous and rotational tillage methods (including ploughing, rotary, moldboard ploughing) at varying tillage depths (10–15, 15–25, 25–35 cm) with different fertilization regimes (chemical vs. organic–inorganic). Among all treatments, the rotational tillage practice that integrates moldboard ploughing at 25–35 cm depth with organic–inorganic fertilization [1200 kg ha−1 mature compost + 375 kg ha−1 compound fertilizer (N:P2O5:K2O = 15:15:15)] significantly reduces bulk density by 11.8% and increases total porosity by 17.9% in the 15–25 cm soil layer. This practice optimizes nutrient stratification, elevating available nitrogen and potassium in the shallow layer (10–15 cm) to 126.13 and 372.45 mg kg−1, respectively, while boosting available phosphorus in the subsoil (25–35 cm) by 247.8%. Furthermore, it significantly enhances soil microbial activity, increasing populations of bacteria, actinomycetes, and fungi by 3.42 × 105, 0.65 × 105, and 2.40 × 103 CFU g−1, respectively, alongside a 49.4% rise in soil respiration. These synergistic improvements collectively promote stable maize yields (increasing by 1731.4 kg ha−1) and high economic returns (net income increasing by 3301.6 CNY ha−1). These findings support the promotion of integrated tillage–fertilization strategies to enhance maize productivity and soil ecological function in semi-arid regions.