Optimized length and application rate of chopped straw for alfalfa production in ridge-furrow rainwater-harvesting in semi-arid regions in China

Water scarcity poses a significant challenge for alfalfa (Medicago sativa L) cultivation in semi-arid regions in China. The conventional use of ridge-furrow rainwater harvesting (RFRH) with plastic film mulching in these areas has led to notable environmental repercussions. This study proposed an innovative approach in which RFRH was integrated with chopped straw-soil crust instead of plastic film. Runoff observations and alfalfa production experiments were carried out using a split-plot design to investigate the impact of varying chopped straw lengths (2 cm and 10 cm) and application rates (0 (R0), 3 (R3), 6 (R6), and 9 (R9) t ha−1) on runoff coefficient, soil water storage, temperature, fodder yield, and crop water productivity (WPC). Results indicated that the average runoff coefficient for R0, R3, R6, and R9 was 0.36–0.49, 0.41–0.59, 0.50–0.68, and 0.64–0.74, respectively. Compared to R0, the increase in soil water storage for R3, R6, and R9 was 7.1–15.1, 15.0–26.5, and 20.1–44.2 mm, respectively. The reduction in temperature within the furrow profile for those treatments was 0.4–1.0°C, 0.8–1.3°C, and 1.1–2.0°C, respectively. The increase in fodder yield for those treatments ranged from 11.3 % to 34.0 %, 31.2 %-62.9 %, and 7.9 %-47.7 %, respectively, while the enhancement in WPC was 1.3–14.8, 5.1–27.9, and 2.0–20.7 kg ha−1 mm−1. Notably, the average values for runoff coefficient, soil water storage, fodder yield, and WPC under 10 cm length of chopped straw were 1.03–1.31, 1.02–1.03, 1.02–1.05, and 1.03–1.08 times greater than under 2 cm length of chopped straw. Runoff coefficient, soil water storage, fodder yield, and WPC increased as chopped straw application rate and length increased. The structural equation modelling analysis showed that the chopped straw application rate had a significant direct positive effect on fodder yield and WPC, whereas the chopped straw length had a significant indirect negative effect on those parameters. The regression equation indicated that the optimized chopped straw application rate ranged from 5.2 to 7.1 t ha−1, while the optimized chopped straw length was 10 cm. This study underscored that chopped straw-soil crust was a sustainable alternative to plastic film mulching, offering valuable insights for improving alfalfa cultivation in water-scarce environments.