Spatial Variability of Soil Moisture Under Sprinkler Irrigation

Crop yield response to sprinkler irrigation depends mainly on the spatial distributions of applied water within the root zone,however,we have quite limited know ledge aboutit.The redistributions of water in the soil were therefore observed under the conditions of sprinkler uniformity (CU) ranging from 53% to 98% and application amount from 5 to 58 mm,on two different soil types—a volcanic ash soil and a sandy loam soil.The distribution of bulk density was examined and showed that it can be represented by a normal distribution function for both soil types.The autocorrelation functions and semivariograms were calculated for water application and soil water content 24 h after application ceased to determine their spatial dependency.Sprinkler water application demonstrated a correlative length of 4 to 6 m,which increased with wind velocity during the experiments,but water applied by a rainfallevent was spatially independent.Soil water contents for 24 hrs after water application ceased exhibited a correlative length of 5 to 6m and appears to be independent of application uniformity.The field experiments also showed that the water was more uniformly distributed in the soil than sprinkler water applied on the ground surface,and the uniformity of water in the soil was closely related to the uniformity of initial soil water content and the total water applied.