Spatial variability in penetration resistance of a hardsetting tropical alfisol

Abstract

Geostatistical techniques were used to analyse the spatial variation of penetration resistance on an experimental plot intended for root studies. Penetration resistance was measured at two soil water conditions. Penetration resistance exhibited spatial structure but the models describing the semivariograms were different for the two soil water conditions. An isotropic linear model provided the best fit for penetration resistance in the dry soil while an isotropic spherical model was used for penetration in the wet soil. A complementary study of the spatial structure of water content also showed a similar trend. Cross-semivariograms were constructed to determine the spatial relationship between penetration resistance and water content. Penetration resistance in the dry soil was negatively correlated with water content. The nugget variances as the percentage of the sill in the wet soil data set suggest that the topsoil was slightly more variable than the subsoil. The spatial scale of variation in penetration resistance of the wet soil was 33 m at 7.5 cm depth and 20–27 m at 15–30 cm depth. Punctual kriging was used to estimate the penetration resistance and water content values. The estimated values are presented as contour maps. The pattern of variation and the underlying possible processes for the variation are discussed. The results suggest that the likely influence of spatial variation of soil properties on crop growth may have to be considered in modelling in order to simulate the real field situation.