Evapotranspiration and potential water saving effect evaluation of mulched maize fields in China

To alleviate the contradiction between crop evapotranspiration (ET) and available water resources, and to develop agricultural production, mulched irrigation, as a water saving technology, is popularized in arid areas of China. However, the observations of ET in long-term mulched farmlands are scarce, so the inter-annual variation and controlling factors of ET after mulching remain uncertain, and the overall water saving effect of mulching in arid areas has not been quantified. Therefore, we conducted the observation experiments (2007-2021) on a mulched maize field, applied the modified Shuttleworth-Wallace model and obtained multi-source data statistics to fill in the gaps in the previous research. The results showed that the mean ET in the past 15 years was 521.68 mm, and the arid areas faced more severe water demand pressure. The inter-annual ET trend of the mulched maize field increased significantly, mainly caused by the reference evapotranspiration (ET0), while the interannual fluctuation was mainly attributed to the crop coefficient (Kc). The contribution of plant transpiration (Tr) to ET was always greater than that of soil evaporation (Es), and the contribution of solar radiation (Rs) to ET was the largest among environmental factors. In addition, based on observation data and model simulation, it was revealed that the water saving amount and ratio of the long-term mulched maize field were estimated to be 83.8 mm and 13.3 %, respectively. Furthermore, the statistical results from 49 sites in five provinces (regions) in Northwest China showed that compared with the agricultural water use in the recent 10 years, the mean annual total potential water saving amount and ratio of the mulched maize field were 2.2 billion m3 and 2.5 %, respectively. Our study will provide important guidance for understanding the variation of crop ET and water resources allocation.