Optimizing drip irrigation managements to improve alfalfa seed yield in semiarid region

Alfalfa, a crucial forage crop, encounters substantial challenges in seed production in semi-arid regions due to drought and soil salinization. To address this challenge, a five-year field experiment was conducted in northwestern China to evaluate the effects of subsurface drip irrigation (SSDI) at different drip line depths and with different irrigation time treatments on alfalfa seed yield, yield components, irrigation water use efficiency (IWUE) and seed quality. The study indicated that SSDI at a depth of 10 cm resulted in a 48% increase in seed yield compared to surface drip irrigation and also obtained the highest IWUE with minimal soil disturbance. While irrigation during the branch, full bloom and pod set stages led to increasing for seed yield and IWUE, it was susceptible to climatic fluctuations during the growth period. Random forest modeling revealed that the timing and quantity of irrigation were key factors that determined yield components and seed yield. Climatic factors, specifically temperature and precipitation, played a significant role at each location. Irrigation time could have an effect on seed size, chlorophyll, and protein concentration analyzed by multispectral imaging. Linear discriminant analysis modeling indicated no significant difference in overall seed quality among the different irrigation time treatments, but prolonged seed maturation for the optimal irrigation time treatment. Therefore, installing the irrigation line at a depth of 10 cm and ensuring irrigation during the branching and full bloom stages were essential, while irrigation at the pod set stage was optional, for significantly improving the seed yield of alfalfa. RF model combined with the meteorology and irrigation management factors could determine key factors for the effect on seed yield. This research would provide valuable theoretical and practical insights for alfalfa seed production in semi-arid regions.