Soil moisture is one of the most important parameters controlling various critical zone processes including energy balance and nutrient cycling. However, hillslope soil moisture variation and its response to rainfall are not fully understood yet. Through real-time monitoring systems, mechanisms of soil moisture response to rainfall were investigated at top, upper, middle, lower and toe slope positions along a typical mixed land-use hillslope in Taihu Lake Basin, China. The corresponding land use types for these five hillslope position are woodland, tea (Camellia sinensis), tea, meadow and woodland, respectively. This hillslope has annual precipitation around 1100 mm. Soil moisture varied from < 0.05 m³ m^− 3at the top slope during the dry period to > 0.40 m³ m^− 3 at the toe slope during wet period. Despite different land-use types, similar characteristics of soil moisture response to rainfall were observed at the top (woodland), upper (tea) and middle (tea) slope positions. At these three sites, degrees of soil moisture change (difference between maximum soil moisture during the rainfall and antecedent soil moisture) were significantly (P < 0.05) influenced by precipitation amount and intensity, as well as antecedent soil moisture in some cases. However, at the lower slope position (meadow), soil moisture variation during the rainfall was mainly influenced by lateral subsurface flow; the cumulative precipitation was less than the increased soil water storage, indicating that water must come from the upslope areas to recharge this site. At the toe slope position (woodland), precipitation interception by tree canopy and surface organic matter reduced the degree of soil moisture change during rainfall events. Lateral subsurface flow can recharge deep soils at the toe slope position in rainfalls > 35 mm with relatively wet initial condition (e.g., soil moisture at 0.1-m depth of this site > 0.30 m³ m^− 3). Results suggest that lower and toe slope positions are hot spots receiving lateral surface and subsurface recharge. Perennial vegetation at toe slope position can remove nitrogen in lateral subsurface flow by promoting denitrification. Therefore, maintaining toe slope area in perennial vegetation may help to mitigate dissolved nitrogen losses from upslope fertilized tea plantations.

Applying N fertilizer at rates that satisfy both economic and environmental objectives are critical for sustainable agriculture. The hypothesis of this study was that the spatial variability in maize (Zea mays L.) yield and its response to N rate were influenced by soil–water-topography dynamics. In 2008 and 2009, a study was conducted along an agricultural hillslope in the Northern Appalachian Ridge and Valley Physiographic Province in the USA with Cambisols according to FAO soil classification. Minimum, maximum, and delta yields and optimum N rate at different slope positions were determined using quadratic-plateau maize yield – N rate models. Results confirmed our hypothesis. The spatial variability of maize yield and its response to N rate was influenced by silt content, soil depth, profile curvature, slope, soil wetness and degree of soil water content temporal variation. In both dry year (2008) and wet year (2009), optimum N rates positively correlated (P < 0.05) with the temporal variation of soil water content, which is an indicator of subsurface flow paths. In 2008, maize yield was little varied along this hillslope (11.7–12.0 Mg ha-1), while greater yield response to N rate (represented as delta yield, 5.6 Mg ha-1) was observed in upper convex and steep slope areas with low minimum yield (6.1 Mg ha-1). However, in 2009, greater maximum maize yield (13.5 Mg ha-1) and yield response to N rate (8.7 Mg ha-1) were observed in lower concave slope areas with deeper soil depth and thus greater water storage. Results from this study suggested that site-specific N applications could be improved by considering within field variability of soil, topography and hydrology.

This is a solid piece of work that could help to establish these research sites as excellent long-term research sites for both basic and applied projects.

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http://www.sciencedirect.com/science/article/pii/S0167198714002153