Different effects of water-saving management on canopy microclimate, spikelet sterility, and rice yield in the dry and wet seasons of the sub-humid tropics in northern Ghana

Abstract Increasing temperatures and water scarcity are concomitant threats to sustainable rice production in future climates. Although both aspects have been widely studied, little is understood about how water-saving management might affect heat-induced stress and grain yield of rice under open-field conditions. The objective was to clarify how water management practices affect daily inner-canopy temperature (Tc) dynamics, flowering time, heat-induced spikelet sterility, and rice grain yield. Field experiments were conducted in four consecutive wet and dry seasons in northern Ghana. Two rice varieties, IR64 and Jasmine85, were grown under two water regimes: 1) continuous flooding (FL), and 2) continuous flooding except for an approximately 20-day drainage treatment at the flowering period (DF). Although the DF treatment was non-flooded, a high moisture content was maintained (>60 % of saturated volumetric water) to avoid any significant drought stress. The effect of water regimes on grain yield and Tc differed significantly between the dry season (DS) and wet season (WS). DF significantly reduced yields by 13–26 % in the DS but not in the WS. However, the effect of DF on Tc at flowering time (0.2–0.3 °C increase) and spikelet sterility (3–5% increase) was relatively small even in the DS. In contrast, DF greatly increased Tc from solar noon to midnight, in particular during the period of ±3 h from sunset in the DS. At this time of the day, DF had a higher Tc than FL by 0.7–0.9 °C on average. The Tc did not differ between DF and FL either at flowering time or nighttime in the WS. The Tc changes over the course of the day imply that water-saving management may have a higher risk of yield reduction in the DS of the sub-humid tropics not only by increasing heat-induced sterility but also by increasing late-afternoon-to-nighttime temperatures, which can cause physiological stress and respiration loss. These results can help improve water-saving management practices under contrasting climatic conditions in the sub-humid tropics and predict the combined effect of increasing temperatures and water scarcity on rice production.