The Role of the Specific Properties of an Andosol as a Water Reservoir to Improve Pasture Growth and Prevent Soil Physical Degradation in Irrigated Grazing Systems

This study analyzed the role of an Andosol as a water reservoir for the improvement of pasture growth under different irrigation schedules considering the short-term effects of grazing/mowing on soil mechanical strength. Water retention curves measured in undisturbed soil samples collected at three depths (10, 20, and 60 cm) and calibrated soil moisture sensors were used to study the water content dynamics under different irrigation schedules (rainfed, 50% and 100% of field capacity) during the summer of 2020 in three types of pastures (Lolium perenne, Bromus valdivianus, and a diverse pasture). The changes in mechanical strength due to defoliation techniques (mowing and grazing) were evaluated by using penetrometers. As the water available in the soil (WAS) increased, the pasture productivity increased as well; however, saving water by restricting its application was feasible (up to 50%) due to the wetting-drying cycles (WD), which showed that when irrigation was applied some of the water infiltrated to deeper horizons. The mechanical strength in the soil under grazed pastures (4500 kPa) was higher as compared to mowed (3900 kPa) pastures. The consideration of the specific physical properties (e.g., plant-available water between 20 and 41% and sensor calibration) permitted a reduction in the amount of water applied with no detrimental effects in pasture productivity. Irrigation reduced mechanical strength, and irrigated soils proved to be more susceptible to animal trampling; however, when the amount of water applied to the soil was reduced, it could better resist animal trampling.