Spatial Variations of Soil Penetration Resistance and Shear Strength and the Effect of Land Use Type and Physiographic Unit on These Characteristics

Investigating spatial variability of penetration and shear strength properties is of particular importance for the management and improvement of agricultural soil fertility for sustainable production. The aim of this research was to investigate the effect of land use type and physiographic units on soil penetration and shear strength, and their spatial variability in Lapoui plain. The soil penetration and shear strength were measured using cone index penetrations and cutting blade at 130 observation points with three replication at the top layer (0-30 cm) in three physiographic units and two land uses in the area. The primary and secondary derivatives of the digital elevation model were also used as covariates. To evaluate the spatial variability of the proposed variables, three covariates including, co-kriging, ordinary kriging, and inverse distance weighting were used. The results of linear correlation showed an inverse relationship between shear strength and penetration resistance and DEM covariates. As a significant inverse relationshipwas observed between shear strength and penetration resistancein the physiographic units of piedmont plain, alluvial plain and hill. The same inverse and significant relationship was also found between the two characteristics in the irrigated and rainfed land use. The co-kriging method for shear and penetration strength based on the coefficient of determination (R2), with values of 0.55 and 0.38, indicated a good performance. Generally, geostatistical methods showed a moderate to poor accuracy in predicting penetration and shear strength. Further work is suggested to investigate the performance of other linear and nonlinear modeling approaches (pedotransfer functions, PTFs) in prediction of the abovementioned soil parameters.