Global synthesis of the impact of droughts on crops’ water-use efficiency (WUE): Towards both high WUE and productivity

Increasing frequencies and intensities of drought associated with climate change are placing great strain on agricultural water availability and crop yields across the globe. Thus, numerous studies have examined factors affecting water-use efficiency (WUE, an important indicator of the balance between productivity and water availability), and ways to improve it. However, conflicting results have been obtained and WUE has generally only been improved at the expense of yield. Here, we performed a meta-analysis to examine the impact of water stress on WUE and identify crops and some water management strategies that could potentially increase both productivity and WUE under water stress. Overall, the meta-analysis of 80 peer-reviewed publications, including 792 observations, showed that crop WUE slightly improved under drought stress (LnRR++=0.015), but the results varied depending on crop type and drought treatments. Moreover, the results indicate that both WUE and yield can be improved under drought stress by identifying appropriate crops (potentially including manioc, canola, rose geranium, spearmint, peanut, wheat, pear-jujube, watermelon, tomato, spinach, and pepper) and water management regimes. Short drought duration (< 30 days) and deficit irrigation throughout the whole season rather than only during the vegetative or reproductive phase are more likely to improve WUE and yield concurrently. Our study is one of the first to analyze factors affecting WUE variation and identify ways to increase WUE and yield simultaneously under drought stress, based on a large set of data from all over the world. The findings may help efforts to formulate practical guidance for future agricultural production as climate change progresses.