Improving/maintaining water-use efficiency and yield of wheat by deficit irrigation: A global meta-analysis

Population growth and climate change are necessitating increases in food production and reduction in amounts of water used for agriculture. Deficit irrigation has been proposed as a strategy to maintain/increase yield while reducing the use of water in agriculture; however, it has not been widely adopted, in part, due to risk of reduced yield. In this paper, we describe a meta-analysis designed to quantify effects of deficit irrigation on wheat water-use efficiency (WUE) and yields, and identify optimal strategies for deploying deficit irrigation to achieve win-win effects of improving WUE and yield simultaneously. Overall, the meta-analysis of 41 peer-reviewed publications collectively containing over 381 observations showed that the win-win relationship between WUE and wheat yield does exist. Overall, deficit irrigation improved wheat WUE by 6.6 % but decreased yield by 16.2 %. However, the results varied, depending on irrigation methods (such as irrigation type, timing and water amount) and environmental factors (such as precipitation, temperature and soil properties). In order to maximize win-win effects and minimize tradeoff between WUE and yield, we found that deficit irrigation is most appropriate for areas where total precipitation during the growing season is less than 200 mm and the soil is loamy or sandy. Deficit irrigation using border and furrow irrigation is more likely to achieve high WUE and yield concurrently than drip or sprinkler irrigation. Importantly, we found that the most influential factors affecting yield and WUE are the irrigation level, and the irrigation thresholds to achieve various scenarios between WUE and yield. Our findings suggest deficit irrigation can improve yield and WUE simultaneously, and identifies the conditions under which these improvements can be realized.