Management practices regulate the response of canopy and ecosystem water use efficiency in cropland ecosystems

Abstract

ContextWith rising global temperature and frequent drought events, water resource supply is facing to great challenge. Understanding the effects of different management practices on cropland water use efficiency (WUE) is crucial to promote effective allocation of water resources and food security. ObjectiveThe objective of this study was to reveal the contrasting effects of different farm management practices including continuous and rotational, tillage and no-till, irrigated and rainfed on cropland water use efficiency from canopy (WUET) to ecosystem (WUEET) scales, respectively. MethodsOn the basis of 26 site-years eddy covariance-based carbon and water flux observations, this study used the underlying WUE (uWUE) model to partition evapotranspiration (ET) across maize and soybean ecosystems. Three control groups were used to compare the effects of different management practices on the coupling relationships between terrestrial carbon and water cycles, respectively. ResultsCompared with the rotational maize-soybean site, both WUET and WUEET at the continuous maize site were larger, which was mainly ascribed to stronger gross primary productivity (GPP) for the C4 crop. But over the maize-planting years, both WUET and WUEET at the rotational site were higher than the continuous site owing to the nitrogen fixation by rhizobia for preceding year, especially for WUET. Under conventional tillage and no-till management, multi-year mean WUEET and WUET were contrasting. WUEET under no-till was apparently larger than WUEET under till, because of similar GPP but relatively lower ET. Meanwhile, more water was consumed by crop transpiration (T) under no-till, which led to lower WUET in comparison with WUET under till. In comparison with the rainfed farming, GPP, ET and T all increased apparently after irrigation. However, both WUET and WUEET at the irrigated site were not improved owing to more water lost with relatively fewer GPP increase. ConclusionsThe study suggested that the crop rotation system can improve both WUEET and WUET apparently. Meanwhile, fewer water resource was consumed by cropland under no-till management. Finally, irrigation farming improved the cropland GPP but reduced WUEET and WUET. ImplicationsOur results provide valuable management implications for understanding the mechanisms that can enhance water use efficiency and result in significant water savings and high yield.