Analyzing the impact of grazing and short-term irrigation management on soil mechanical strength of a volcanic ash soil under different types of pastures

Abstract

In southern Chile, there are over 1.3 million ha of pastures on volcanic ash soils. The climate change scenario and the need to increase yields are forcing farmers to increase irrigated surface areas. This implies an intensified soil use that must be analyzed to prevent soil degradation. Therefore, this study analyzed the impact of initial pasture defoliation (mowing and grazing) and short-term irrigation managements on soil structure dependent properties of a volcanic ash soil under different types of pastures. Field penetration resistance (PR) profiles (0–80 cm), soil water content measurements (0–10 cm) and undisturbed soil samples (0–3 cm) displayed the impact of animal trampling due to repeated loading events. Though this experiment did not determine significant interactions such as pasture x defoliation method x applied load, the early developmental stage of this experiment provided a basis for better understanding deformation processes due to animal trampling when different types of pastures are irrigated in the short-term. The plastic deformation caused by loads higher than precompression stress induced an increase in soil mechanical strength (e.g. Pc increased after the first grazing, but not after mowing), affecting the macropore volume and air permeability. The short-term effects (<2 years) showed the incipient consequences of grazing and irrigation: PR increased due to animal trampling (data dispersion: grazed> mowed plots, showing footprint formation after 8 grazing events) and the higher sum of PR in non-irrigated pastures evidenced the increase of the cohesion between particles/aggregates after drying events. Therefore, it can be expected that in the medium-term (3-4 years), animal trampling could lead to significant soil deformation and a progressive increase in soil mechanical strength near the soil surface.