Temporal Dynamics and Stability of Spatially Measured Soil Water Status in Crop and Grass Systems.

Soil water status and its spatial and temporal variability are of great importance to hydrological modeling and agricultural management.  Changes in meteorological conditions, especially precipitation, usually cause large temporal dynamics in soil water status; whereas, inherent soil properties maintain its spatial pattern with time. The objective of this study was to analyze the temporal dynamics and stability of field soil water status measured at different soil depths across two land use systems. Along a 48- by 3-m transect evenly across cropland and grassland, soil matric potentials at depths of 10, 30, 50, 70, 90 and 110 cm were investigated at 1-m intervals using a hexagon nest of six tensiometers on a weekly basis from May to October in 2013. The results showed that at 10 and 30 cm, matric potential varied much more pronouncedly in time than in space and the standard deviation along the transect decreased with precipitation amount. According to wavelet and autocorrelation analysis, temporal dynamics in both soil water status and its spatial structure diminished with soil depth. The spatial autocorrelation ranges at the upper three depths were significantly longer than those in the deep soil. In contrast, temporal stability of soil matric potential generally increased with soil depth. The temporal autocorrelation ranges were the shortest at 10 and 30 cm. Significant negative rank correlation coefficients were only obtained at these two soil depths when either a very wet or very dry spatial series was included in the correlation. At 10 cm, this phenomenon could be explained by the relationship between soil water status and soil texture; while at 30 cm, it may also relate to the flow conditions in the overlying layers.