Effect of grazing density on the bearing capacity and functionality of the pore system of an Andisol

Abstract

Grazing management is a dynamic process that affects both the plants and the soil that supports them. The objective of this work was to evaluate the effect of grazing density on the bearing capacity and the functionality of the porous system of a Duric Hapludand, analysing its recovery. Two grazing densities of 50 and 200 cows ha-1 were established on a natural pasture regenerated with Lolium perenne L. and Trifolium repens L. (20x20 m2 plots). In each experimental unit, disturbed and undisturbed soil samples (2 to 10 cm) were collected in different moments: 1 day before grazing, 1 day after the last grazing and after a lag period of 105 days without grazing. On the undisturbed and packed samples at the same bulk density, the bearing capacity (CS, at 6 kPa of tension) was determined with static loading test (CS_est) and cyclic loading test (CS_din). Additionally, the bulk density (da), air capacity (AC), air conductivity (Kl) and coefficient of linear extensibility (COLE) were determined. It was observed that continuous grazing affects the mechanical stability of the soil and the functionality of its pores. An increase in the grazing density during winter increases the CS value of the soil, being higher when calculated with CS_din. However, this relationship was not observed when analysing soil resilience. There were no critical values for the development of plant roots; however, it does not mean that these soils can endure stresses indefinitely.