Irrigation quality has been described by calculated parameters assuming that water storage capacity in soil is a constant. However, this property presents spatial variations. Concern with environmental and economic aspects has led to culture management in specific areas, a fact which requires knowledge of spatial distribution of soil properties. Geostatistics makes possible the identification of the spatial dependence structure and the mapping of a given soil property. The objective of this work was to identify sampling and block kriging intensities, adequate to estimate soil water storage with enough precision to characterize irrigation quality. A radial transect was sampled each 2.83 m, in 56 locations in a center pivot-irrigated area at ESALQ/USP, São Paulo, Brazil. At each point, the water storage capacity in soil was determined at pressures varying between 0.01 and 0.08 MPa at 0-3 m depth. Based on the semivariogram obtained for the transect data, kriging was performed in blocks of different lengths varying between 2 and 30 m and simulated sampling spacings between 2 to 20 m, in the transect direction. From these values, the available soil water storage at 0.30 m soil profile was calculated. The block kriging variance and deep percolation water volume were obtained for each block kriging combination. To quantify deep percolation, it was assumed that the constant depth of applied irrigation was equal to the mean soil water storage. The results showed that block kriging must be performed with a 2 m block length, provided computer resources are not limiting factors. Increasing the soil sampling intensity did not promote interpolation. Thus, a 20 m grid may be used but a 10 m grid should be more appropriate. Short range sampling should be performed to identify the semivariogram at lower distances. Although it promoted smoothing, block kriging must be used to describe the spatial pattern of the soil water storage, since it allows a better evaluation of excess and deficit volumes and, mainly, the identification of the sites where they occur.
spatial variability; available soil water; sampling; center pivot