Rice yields and water use under alternate wetting and drying irrigation: A meta-analysis

Rice systems provide a major source of calories for more than half of the world's population; however, they also use more water than other major crops. Alternate wetting and drying (AWD) is an irrigation practice (introduction of unsaturated soil conditions during the growing season) that can reduce water inputs in rice, yet it has not been widely adopted, in part, due to the potential for reduced yields. We conducted a meta-analysis to: 1) quantify the effect of AWD on rice yields and water use; and 2) to identify soil properties and management practices that favor AWD yields and promote low water use relative to continuous flooding (CF- control). We analyzed 56 studies with 528 side-by-side comparisons of AWD with CF. Overall, AWD decreased yields by 5.4%; however under Mild AWD (i.e. when soil water potential was >= -20 kPa or field water level did not drop below 15 cm from the soil surface), yields were not significantly reduced in most circumstances. In contrast, Severe AWD (when soils dried beyond -20 kPa) resulted in yield losses of 22.6% relative to CF. These yield losses were most pronounced in soils with pH >= 7 or carbon <1% or when AWD was imposed throughout the season. While water use was lowest under Severe AWD, under Mild AWD water use was reduced by 23.4% relative to CF. Our findings both highlight the potential of AWD to reduce water inputs without jeopardizing yield as well as the conditions under which these results can be realized. (C) 2017 The Authors. Published by Elsevier B.V.