Evaluation of the effectiveness of irrigation methods and fertilization strategies for alfalfa: A meta-analysis

Alfalfa (Medicago sativa L.) plays an important role in livestock production in most regions of the world, but the quantity and quality of alfalfa have been critically affected by drought events in recent years. Thus, quantifying the efficacy of widely used strategies, irrigation methods and fertilization that are aimed at improving drought resistance in alfalfa is a worthy topic that has been addressed in a variety of ways using both field observations and simulation models. Although such strategies play a critical role in climate change adaptation, the global patterns of these strategies in a changing world remain elusive due to regional differences, such as drought features, strategy design and environmental conditions. Thus, by using effect size and statistical analyses, we synthesized three variables, namely, alfalfa yield, water use efficiency (WUE) and crude protein (CP), to examine the efficacy of irrigation methods and fertilization in drought areas based on peer-reviewed papers from 1990 to 2022. Our results showed that increasing drought stress reduces the alfalfa yield (-34.4%) but can increase the WUE (+13.7%). Both yield and WUE showed a negative relationship with the water deficit, but this phenomenon can be improved by using appropriate irrigation. The yield losses of alfalfa can be offset by implementing a fertilization strategy (+22%) under drought stress, especially for phosphate fertilizer. Overall, our results provide some evidence for the climate change adaptation of alfalfa under drought stress and indicate that fertilization is a more effective adaptation to improve alfalfa drought resistance (both yield and WUE, and yield and CP) than the irrigation method, which shows better performance in improving alfalfa WUE. Our synthesis of the effectiveness of irrigation methods and fertilization on alfalfa drought resistance can be used to develop scientific strategies for climate change adaptation for alfalfa and agriculture under climate change.