The Influence of Soil Texture on Spatial Variability of the Cone Index in a Sandy Loam Soil (Eutric Leptosol)

by Open Science Repository Agriculture
(October 2013)


Geo-referenced penetration resistance measured as Cone Index CI, were conducted in a 54 (9 by 6) grid cells each 10 m² on a sandy loam soil (Eutric Leptosol) of the University of Juba demonstration farm in October 2012. Undisturbed soil core samples were extruded at 30 cm depth for the determination of the soil fractions and texture. An Eikjelkamp handpush penetrologger was used to determine the cone index. The results showed that correlations between the CI and sand, silt and clay contents at (P<0.05) were significant though for sand this was very weakly positive (r²=0.03) and weak for silt (r²=0.133) and hardly any for clay (r²=0.01) fractions respectively. The result of this study showed that the mean penetration resistance or Cone Index varied between 1.2-1.9 MPa with a critical value of CI, tα=2.41 MPa significant at (P<0.05). The results showed that the critical CI value was attained with textural composition of silt and clay at values 63.53% and 11.01% respectively (P<0.05). This suggested that higher CI in the soil was contingent on the critical amounts of especially silt and clay. Sites on the experimental plots that were originally cultivated a year earlier on in 2011 showed CI values ranging between 1.2 to 1.7 MPa while this was between 1.7 to 2.8 MPa for previously uncultivated sites. A spherical model of the isotropic semi-variogram gave the best fit for both ordinary kriging and Inverse Distance Weighted (IDW) methods with no significant differences in the separation distance, h at 13.10 m, semi-variance γ or sill at 0.334. The semi-variances for both methods was constant over the entire separation distance suggesting spatial dependence. The results of this study clearly indicated that the penetration resistance of the Eutric Leptosol was a function of the soil texture.

Keyword: spatial variability, cone index, ordinary kriging, Inverse Distance Weighted.

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The Influence of Soil Texture on Spatial Variability of the Cone Index in a Sandy Loam Soil (Eutric Leptosol)

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