Capacity and intensity parameters of the pore system for the evaluation of the soil physical quality of an andisol under grazing

Abstract

Pastures in southern Chile are the main livestock feed throughout the year, whereas grazing events, depending on soil mechanical stability, may affect soil physical functions. In these terms, the soil physical quality is a concept, which can be determined through the response of the soil porous system functionality to the application of internal and external stresses. The purpose of this study was to analyze the effect of cattle grazing on the temporal evolution of the capacity and intensity parameters of the Andisols porous system. Six soil samplings were conducted (2-10 cm depth; the most affected by grazing), and properties such as volumetric soil water content, precompression stress (CS), air capacity (AC), air (k_l) and saturated hydraulic (Ks) conductivity, coefficient of pore shrinkage, and bulk density (Da) were determined. All investigated properties present temporal variations, caused by grazing events and natural wetting and drying cycles. The values defined as critical for soil compaction, have a restricted applicability in Andisols: i) while the values of bulk density are far from representing compaction problems (1.7 g cm^-3), ii) the AC (< 8%) and k_l (<12*10^-4 cms^-1) of these soils may manifest problem of soil physical quality. Finally, despite of the low Da of the Andisol, an increase in the grazing intensity during winter did not affect any investigated property negatively, highlighting the good physical quality of this soil. However, considering the properties of soils for which the critical parameters were determined, further studies are needed for Andisols to determine the range of their soil quality parameters.