Spatial-Temporal Variability of Soil Moisture As Affected By Soil Properties During Irrigation Cycles.

Temporal change of spatial soil water distribution and its correlation with topography and soil properties (texture, bulk density, and carbon content) were studied in a furrow irrigated 7.56 ha vineyard located in northwestern China. Soil water measurements were taken 17 times from May to October, 2012 and at two soil depths of 0 – 20 cm and 20 – 40 cm of 135 geo-referenced locations. There were four irrigation events during the study period. Coefficient of variation (CV) of spatial soil water ranged from 14.5 to 25.8%, and decreased with higher spatial mean soil water content. The relation between CV and mean soil water content was found similar between the two soil layers. Soil water content was significantly and consistently correlated with soil texture and bulk density, while correlations with topography were most insignificant. Correlation of soil water content with soil sand content were stronger at the later period of an irrigation cycle when soil was drier than that at the earlier period when soil is wetter. Spatial structure characterized by semivariograms of standardized soil water content were found similar at different period of irrigation cycles, and ratios between nugget and sill values of the fitted semivariogram model suggested that relatively larger portion of spatial variability in soil water content was spatially-structured at the surface soil than at the subsurface soil.