Contents lists available at ScienceDirect Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat Factors afecting crop water use efciency: A worldwide meta-analysis N. Mbava a , M. Mutema b, *, R. Zengeni a , H. Shimelis a , V. Chaplot a,c a SAEES, University of KwaZulu-Natal, PB X01, Scottsville 3209, Pietermaritzburg, South Africa b Agricultural Research Council-Institute for Agricultural Engineering, PB X519, Silverton 0127, Pretoria, South Africa c Institut de Recherche pour le Développement (IRD), Laboratoire d'Océanographie et du Climat: Expérimentations et approches numériques, UMR 7159, IRD-CNRS-UPMC- MNHN, 4 place Jussieu, 75252 Paris Cedex 05, France ARTICLE INFO Keywords: Climate variability Crop water use efciency Crop management Photosynthetic process Soil water availability ABSTRACT Water is a limiting natural resource for agricultural production. While it is well accepted that crop types difer in their water use efciency (WUE), there is no consensus on the main factors afecting WUE of main feld crops, which was the motivation of the current study. The efects 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 confrmed that crop type had a signifcant efect (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 ), fbre 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 efcient 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 efcient crop under well-watered conditions (9.90 kg m −3 ), but sorghum was the most efcient 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. 1. Introduction Water scarcity is a major global environmental problem of the 21st century (Srinivasan et al., 2012). Globally, agriculture accounts for 80–90 % of all freshwater used by humans, and most of that water is used for crop production (Morison et al., 2008). While irrigation de- velopment has increased crop productivity in arid and semi-arid areas for decades, water scarcity and escalating costs of setting and managing the infrastructure hamper further expansion of irrigation in developing countries. Rising demand for water by other sectors such as domestic, mining, industries, the environment and, recently, severe pressures from climate uncertainties, exacerbates water shortages for further ir- rigation development. Therefore, there is need for new paradigms for agriculture to, at least, keep pace with rising demand for food while using the lowest possible amounts of water. Diferent disciplines defne water use efciency (WUE) diferently. Originally, crop physiologists defned WUE as the amount of carbon assimilated and crop yield per unit of transpiration (Viets, 1962) and later it was referred to as amount of biomass or marketable yield per unit of evapotranspiration. Irrigation scientists view WUE as a ratio of total irrigation water transpired to water diverted from the source (Israelsen, 1932), while crop scientists defne it as the ratio of total biomass or grain yield to water supplied (Sharma et al., 2015). The present paper adopted WUE as the ratio of grain yield achieved to the amount of water made available to the crop (i.e. stored in the soil plus rainfall and irrigation water). It is expressed as grain yield per unit of land area (Y, kg m −2 ) divided by the amount of water consumed by the crop per unit land area (ET, m 3 m −2 ), usually reported as mm of water needed to produce that yield (Blum, 2005). The need for crops to be drought tolerant and have higher WUE has been the focus of breeding eforts for many years (Sivamani et al., 2000; Tilman et al., 2002; Condon et al., 2004; Blum, 2005; Ruggiero et al., 2017) to alleviate water scarcity and food insecurity. Improved soil fertility and crop management practices have also been developed to enhance better yields with less water (Evans and Sadler, 2008; Busari and Salako, 2013; Busari et al., 2015; Wang et al., 2018). However, water scarcity remains an issue and there is still need for better un- derstanding of the underlying controls of crop WUE. https://doi.org/10.1016/j.agwat.2019.105878 Received 6 September 2018; Received in revised form 16 September 2019; Accepted 22 October 2019 ⁎ Corresponding author. E-mail address: vincent.chaplot@ird.fr (M. Mutema). Agricultural Water Management 228 (2020) 105878 0378-3774/ © 2019 Published by Elsevier B.V. T