Soil water content temporal-spatial variability of the surface layer of a Loess Plateau hillside in China

Surface soil moisture exhibits an important variability in terms of spatial and temporal domains, which may result in critical uncertainties for agricultural water management. The purposes of this study were (i) to characterize the temporal dynamics and stability of the spatial variability of the surface 0-6 cm soil water content theta on a hill-slope; (ii) to investigate issues related to soil moisture conditions including dominating factors on Soil Moisture and to the estimation of the mean theta. During a period of more than one month theta was measured on thirteen days by Frequency Domain Reflectometry using a 10 x 10 m grid of measurement points covering a 60 x 280 m domain within a hill-slope of the Loess Plateau in China. Soil water content exhibited a moderate variability for each measurement date, and the correlation length (lambda) for theta ranged from 8.4 to 27.7 m. With the soil becoming drier, lambda decreased, the CV% and the sampling number for accurate mean 0 estimation increased. Aspect, elevation, organic matter content, clay content, and bulk density were the main influencing factors, whose extent of influence weakened with decreasing theta. Based on time stability analysis and on the correlation of mean relative difference of theta with the relative difference of dominating factors, mean theta values were well estimated, with a better accuracy under wetter conditions.