Spatial Distribution of Soil Moisture and Fine Roots of Apple Trees under Water Storage Pit Irrigation

This study was conducted to determine the spatial distribution of soil moisture and fine roots (white, diameter <2 mm) growth under water storage pit (WSP) irrigation of apple trees in an experimental apple orchard. Three irrigation treatments have been used since 2009-WSP60 (water storage pit irrigation, pit depth 60cm), WSP40 (water storage pit irrigation, pit depth 40cm), and CK (border irrigation)-in controlled trials. In the considered soil profile of a 0-2m depth, the soil moisture was mostly distributed in the middle-deep soil layer (40-150cm) of the rhizosphere of apple trees, yet this was lower at a depth of 0-40cm under WSP (WSP60 or WSP40) irrigation. For CK, the soil moisture was mainly concentrated within a depth of 0-60cm of the rhizosphere of apple trees. Compared with CK, the fine root length density (FRLD) in the surface soil (0-40cm) was reduced by 7.52-7.56% under WSP (WSP60 and WSP40) irrigation, whereas in the middle-deep soil layer (40-110cm), it increased by 10.32-11.70%. The total amount of FRLD in a 0-2m soil profile under WSP irrigation was 1.19-1.10 times that under CK. The FRLD increased, and the location of the highest concentration of fine roots deepened under WSP (WSP60 and WSP40) irrigation. Thus, this method benefited roots by allowing them to absorb water in a wider area and improving drought resistance. The results obtained provide a theoretical basis for application of the WSP irrigation method.