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

TLDR

Rice is a staple crop that consumes more water than other major cereals, and alternate wetting and drying (AWD) irrigation can reduce water use but is underused because of potential yield losses. The study performed a meta‑analysis to quantify AWD effects on rice yield and water use and to identify soil properties and management practices that favor AWD yields relative to continuous flooding. The authors analyzed 56 studies comprising 528 side‑by‑side AWD versus continuous flooding comparisons. Overall, AWD lowered yields by 5.4 % but, when applied mildly (soil water potential ≥ –20 kPa or water level not falling below 15 cm), yields were not significantly reduced, whereas severe AWD (soil drying beyond –20 kPa) caused 22.6 % yield loss—especially in soils with pH ≥ 7, carbon < 1 % or when AWD was applied throughout the season—yet it also reduced water use, with mild AWD cutting water use by 23.4 % relative to continuous flooding.

Abstract

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.