Alfalfa-winter wheat rotations stabilize yields and maintain soil water sustainability under precipitation variability

Global climate change caused variation in precipitation patterns has become a threat for food security, especially for semi-arid rainfed farming system, i.e., the Loess Plateau. Whether short-term alfalfa-winter wheat rotations could serve as sustainable alternatives to winter wheat monocropping regarding yield stability and soil water sustainability is uncertain. A four-year field experiment (2018–2022) was conducted under three precipitation gradients (P − 30, P0, P + 30). Four cropping patterns were established: continuous winter wheat monocropping (WWWW), and rotations with 1-year (AWWW), 2-year (AAWW), and 3-year (AAAW) alfalfa phases followed by winter wheat. Compared with WWWW monocropping, average annual grain yield increased by 9.5%, 27.2%, and 30.9% in AWWW, AAWW, and AAAW rotations, while yield variability decreased by 29.1%, 27.5%, and 21.2% (P < 0.05). As alfalfa stand age increased, dynamic soil water storage in the 0–300 cm profile (SWS0–300 cm) variability progressively shifted from 0 to 100 cm to 0–260 cm. By 2022, average SWS0–300 cm was 41.1 mm, 13.7 mm, and 2.8 mm higher in AWWW, AAWW, and AAAW than in WWWW, with differences most pronounced below 120 cm. Total water productivity over the experimental period was 3.97, 8.01, and 11.12 kg ha−1 mm−1 higher in rotations than in monocropping (P < 0.05). Our results demonstrated short-term alfalfa-winter wheat rotations enhanced grain yield, yield stability, and water productivity through stratified soil water utilization and improved deep soil water stability. This provided a practical management strategy for sustainable agriculture in semi-arid rainfed regions to cope with variable precipitation regimes.