Compressibility and elasticity of a Vertissol affected by the intensity of grazing cattle

The supply of pasture quantity and quality in areas of native grassland is goal of ranchers. In this study we evaluated the impact of three grazing intensities by beef cattle in an area of unspoilt countryside with improved white clover and red cloveron soil bulk density (Bd), pre-consolidation pressure (sp), compression index (Ci) and the relaxation index (Ri) in a Vertisol derived from basalt. The experiment was conducted in an area of unspoilt countryside with improved white clover and red clover, subjected to three intensities of grazing, located in the experimental field of INIA Glencoe, in the Centre-North of Uruguay (Latitude: 32 degrees 41'S and Longitude: 56 degrees 16'W). The soil has a depth of 0.92m, clayey silt (0.58kg kg(-1) clay) and has granular structure. The intensity of grazing configured the treatments: no grazing (SP), grazing with low load (consisting of grazing animals per hectare from 20 to approximately 385kg of body weight, during 4 days) (PCB) and grazing with high load (40 animals per hectare of approximately 385kg live weight, during 4 days) (PCA). Statistical analysis consisted of comparing averages of Bd, sp, Ci and Ri in the three soil treatments by Student's t test at 5% of significance. PCA caused no increase in relation to the Ds SP nor significant changes sp and Ic, indicating that the bulk of the organic material provided on the surface of Vertisoil high load bearing capacity, low compaction susceptibility and high elasticity of the soil. The most superficial layer of Ri with respect to subsurface conditioned more resilient deformation, because the PCA were no significant changes in sp and Ic against the SP and PCB.