Structural changes of an Andisol with contrasting pasture coverages

Abstract

In Southern Chile, pastures are the most used feed component in livestock systems. Excessive grazing can alter the mechanical and hydraulic properties of the soil causing a negative effect on its structure. Temporal changes caused by sheep grazing on soil mechanical and hydraulic properties were evaluated under contrasting grassland cover conditions.

Four types of pastures were established on an Andisol (T1-Mixed; T2-Multispecies; T3-Naturalised without fertilisation; T4-Naturalised with fertilisation), which were grazed with an instantaneous stocking rate of 625 ewes ha^-1. Post-grazing (Dec. 2010 and Oct. 2011) undisturbed soil samples (0-10 cm) were collected to determine soil bearing capacity (CS) and soil air conductivity (kl).

Soil CS ranged from “very low” (< 30 kPa) to “low” (30-60 kPa) over a range of 7 kPa (T2-2011) to 57 kPa (T3-2011). Convective air fluxes (kl) were below the threshold value of -3.26 log cm s^-1, independent of measurement year or meadow type. However, the average air fluxes for T3 and T4 were -3.9 log cm s^-1 and -4.6 log cm s^-1 for T1 and T2. The relationship between CS and kl in the 2011 season (p = 0.011; R² = 0.978) suggests an increase in soil structural stability associated with mineral fertilization that

allowed greater root development and air flow in soils that maintained their structure.