Spatiotemporal Variability of Soil Moisture as Affected by Soil Properties during Irrigation Cycles

Information on spatiotemporal soil water variability and its association with soil properties during multiple irrigation cycles is important for precisely estimating soil water storage and developing effective irrigation strategies. Temporal change in the spatial soil water distribution and its correlation with topography and soil properties (texture, bulk density, and C 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 soil depths of 0 to 20 and 20 to 40 cm at 135 georeferenced locations. There were four irrigation events during the study period. The 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 to be 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 mostly insignificant. The correlation of soil water content with soil sand content were stronger during the late period of an irrigation cycle when the soil was drier than at the earlier period when the soil is wetter. The spatial structure of the standardized soil water content, characterized by variograms, was found to be similar at different periods of irrigation cycles, and nugget/sill ratios of the fitted variogram model suggested that a relatively larger portion of spatial variability in soil water content was spatially structured at the surface than in the subsurface soil.