Factors affecting crop water use efficiency: A worldwide meta-analysis

Water is a limiting natural resource for agricultural production. While it is well accepted that crop types differ in their water use efficiency (WUE), there is no consensus on the main factors affecting WUE of main field crops, which was the motivation of the current study. The effects of rainfall pattern, soil type and climatic regime on crop WUE were evaluated using data from 514 experiments around the world published in ISI journal papers. The results confirmed that crop type had a significant effect (p < 0.05) on WUE with cereals producing on average 2.37 kg of dry grain per cubic meter (m−3) of water followed by oilseeds (0.69 kg m−3), fibre crops (0.45 kg m−3) and legumes (0.42 kg m−3). Amongst cereals, maize (3.78 kg m−3) and sorghum (2.52 kg m−3) were more water-use efficient than wheat (1.02 kg m−3), barley (1.21 kg m−3) and millet (0.47 kg m−3). Overall, maize was the most water use efficient crop under well-watered conditions (9.90 kg m−3), but sorghum was the most efficient under dry conditions (5.99 kg m−3). WUE of crops increased from desert to tropical through sub-tropical climate. Moreover, WUE tended to correlate positively with soil organic carbon content (r = 0.86) and negatively with clay content (r=−0.78) and soil bulk density (r=−0.85). These results provide information that is important for making decisions on crop selection in a context of increased climate variability and for crop variety development with enhanced WUE. However, there is need for more research to gain more understanding of the mechanisms responsible for the observed trends and causes of the unexplained variability.