Changes in rainfall partitioning and its effect on soil water replenishment after the conversion of croplands into apple orchards on the Loess Plateau

Abstract

The partitioning of rainfall by plant canopies into throughfall (TF) and stemflow (SF) affects the process of rainfall infiltration into the soil as well as the ecological functions of soil water. A change in land use from croplands to orchards inevitably influences the preexisting rainfall partitioning and soil water replenishment processes. However, few studies have focused on the differences in TF and SF and their effects on soil water replenishment after converting croplands into apple orchards. Thus, the objectives of this study were to quantify the differences in TF and SF between maize (Zea mays L.) and apple trees (Malus domestica, cv. Fuji), clarify their influencing factors, and compare the efficiency of soil water replenishment by rainfall from June to September as well as the soil water content and storage in each hydrological year of the study. Under the same rainfall conditions, the rainfall was distributed differently due to the presence of the maize and apple tree canopies. The sum of the TF and SF in the maize field (129.1 mm and 167.6 mm) was lower than that in the apple orchard (250.4 mm and 354.2 mm) in 2017 and 2018, respectively; the TF amount in the apple orchard was on average 3.4 times that in the maize field, while the SF amount in the maize field was on average 12.9 times that in the apple orchard. The TF percentage ranged from 0 to 76.9 % and 0 to 97.9 % for the maize field and the apple orchard, respectively, while the SF percentage ranged from 0 to 37.5 % and 0 to 3.3 %. The soil water input sources for the maize field were TF and SF, while the input source for the apple orchard was mainly TF. TF and SF production increased linearly with rainfall in the apple orchard. The rainfall amount was identified as the variable with the greatest influence on rainfall partitioning among the rainfall factors considered. An increasing leaf area index resulted in decreasing relative TF but increasing relative SF for maize and decreasing relative TF and SF for apple trees. The mean efficiency of the replenishment of soil water by rainfall in the maize field (30.8 % and 37.4 % in 2017 and 2018, respectively) was slightly lower than that in the apple orchard (34.4 % and 41.0 %). This study provides insight into water cycle analyses aimed at understanding rainfall partitioning and the soil water environment within croplands converted into apple orchards on the Loess Plateau and in other, similar regions.