Importance of Temporal Scale in Assessing Changes in Soil-Water Storage in Apple Orchards on the Chinese Loess Plateau

Knowledge of changes in soil-water storage (SWS) at multiple scales in apple orchards is important for formulating policies for the scientific management and sound planning of apple plantations on the Loess Plateau in China. In this study, we measured precipitation, partitioned evapotranspiration (ET) into canopy interception, transpiration, and soil evaporation, and calculated the changes in SWS using the water-balance method at multiple scales in two neighbouring apple orchards (8 and 18 years old) on the Loess Plateau from May to September in 2013, 2014, 2015, and 2016. The results showed thatETwas consistently lower for the 8- than the 18-year-old orchard in each year at the same scale (p< 0.05). The changes in SWS differed between the two orchards at the same scale, but the trends of change were similar in each year. The trend of the change in SWS at the same scale differed amongst the years for both orchards. The maximum supply of water from soil reservoirs for the two orchards also differed at different scales in each year and was higher at a daily cumulative scale than a monthly and annual scale in 2013, 2014, and 2016. The daily cumulative scale was thus a more suitable scale for representing the maximum contribution of the soil reservoir to supply water for the growth of the orchards during the study periods. Changes in SWS at a daily cumulative scale should be considered when assessing the effect of apple orchards on regional soil reservoirs on the Loess Plateau or in other water-limited regions.