Temporal stability analysis identifies soil water relations under different land use types in an oasis agroforestry ecosystem

Abstract The spring wheat–shelterbelt–maize agroforestry ecosystem is one of the most common land use patterns occurring in oasis agriculture in the arid zones of northwest China. Soil water interactions were hypothesized to exist between adjacent land use types, and that these interactions could be analyzed by using the soil water content (SWC) measured at the most time-stable locations (MTSLs) under each land use type. Objectives of this study were to (1) identify the MTSLs for the different soil layers under each land use type and (2) to investigate the soil water relations between adjacent land use types using the SWC measured at the identified MTSLs. The SWC was measured in 2012 and 2013 at 10-cm depth intervals within 0–260 cm soil profiles at 36 locations along three transects that passed through spring wheat, shelterbelt, and maize subplots. A time-stability analysis of SWC was used to identify the MTSLs in the four different soil layers under each of the three land use types. The results indicated that temporal variations in soil water in the same soil layer among the three land use types tended to have similar patterns. The SWC of the different soil layers under maize exhibited the highest temporal stability among the three land use types. The SWC measured at the MTSLs identified for each soil layer under each land use type was proven to represent their mean SWC. Correlation analyses of the SWCs measured at the MTSLs between two land use types indicated that soil water relations occurred between adjacent land use types but not between those that were non-adjacent land use types by the correlation analyses of the SWCs measured at the MTSLs between two land use types. In the upper soil layer (0–200 cm), soil water relations were mainly affected by shelterbelt root water uptake from the adjacent cropland into which the tree roots had extended. In the lower soil layer (200–260 cm), the soil water relations among the three land use types were due to groundwater recharge, which was a result of crop irrigation that had raised the water table to a level at which it could replenish this soil layer.