Innovative Tillage Practices to Establish Productive and Sustainable Forage Production Systems in Degraded Alfalfa Pastures in Semiarid Regions

Tillage management practices play a critical role in maintaining sustainable forage production systems in degraded alfalfa (Medicago sativa L.) pastures. However, climate change leads to the precipitation exhibits greater variability, the impacts of tillage practices on alfalfa productivity and forage quality as well as the relationships between water consumption and soil properties remain poorly understood. The field trial conducted from 2018 to 2020 aimed to investigate the impacts of different tillage treatments (i.e., no tillage [CK], strip subsoiling tillage [ST], strip rotary tillage [RT], and strip rotary tillage after strip subsoiling [SRT]) on soil properties, water use efficiency (WUE), and forage productivity. Compared with CK, tillage practices significantly increased forage biomass and crude protein yield (CPY), particularly in the case of the SRT treatment, in which the increase was 20.8% and 25.3% higher, respectively (p < 0.05). Meanwhile, the net income in the SRT treatment exhibited the greatest value (US $1922.0 ha⁻¹), showing a 17.0% increase compared with that in the CK treatment. The relationship of soil structure and crop water consumption became evident when tillage practices were applied in the degraded alfalfa pasture. The soil bulk density under the ST, RT, and SRT treatments decreased by 6.9%, 5.4%, and 8.6%, whereas the soil porosity increased by 8.6%, 6.7%, and 10.7% in the 0–60 cm soil layer, respectively (p < 0.05). Furthermore, the soil water content at a depth of 0–60 cm increased by 12.1% in the SRT treatment compared with the CK treatment at the harvesting stage, and the SRT treatment obtained the highest WUE of dry matter (16.9 kg ha⁻¹ mm⁻¹) and precipitation use efficiency of dry matter (15.8 kg ha⁻¹ mm⁻¹). In addition, total nitrogen in the ST, RT, and SRT treatments increased significantly by 21.4%, 11.1%, and 27.0%, respectively, and soil organic carbon in the ST, RT, and SRT treatments also increased significantly by 5.5%, 3.3%, and 10.4%, respectively, compared with those in the CK treatment (p < 0.05). Our study has demonstrated that tillage practices can optimize soil structure, improve water utilization, and increase soil fertilizer for enhancing forage productivity. The SRT practice could be a preferable approach for sustainable agricultural production of degraded alfalfa grassland in the semiarid region of China.