Effect of pasture improvement managements on physical properties and water content dynamics of a volcanic ash soil in southern Chile

The pastures in Chile are sustained on volcanic ash soils covering an area of 1,340,000 ha. Since 44% of these pastures are degraded, different strategies to improve these prairies have been implemented. This study examined the impact of the different pasture improvement managements (PIMs) on soil physical properties, water content dynamics and pasture productivity of a volcanic ash soil under sheep grazing. The experiment was established on a Duric Hapludand and considered four types of PIMs (fertilised-naturalised pasture, cultivated pasture, direct-drilled pasture, diverse-direct drilled pasture) including the initial situation (non-fertilised naturalised pasture). The effect of PIMs and grazing events on bulk density (BD), plant available water (PAW), air permeability (k(a)), saturated hydraulic conductivity (Ks) and pre-compression stress (Pc) in the topsoil (0-10 cm) was determined taking undisturbed soil samples, whereas the penetration resistance (PR), field air permeability (k(1) field) and herbage mass production were measured in the field. The volumetric water content, matrix potential and soil temperature were continuously registered at different depths. The fertilisation of degraded naturalised pastures, without soil structure disturbance, improved the pasture yield (140%), reaching values comparable to those improved with conventional systems. In the short term, the volume of macropores does not change significantly as a function PIMs. However, tilled soils presented less connected pores compared to the non-cultivated PIMs. The conservation of soil structure plays an important role in water accessibility by plants, so that fertilised-naturalised pastures were able to absorb water to depths of up to 60 cm. Compared to the improved pastures, the degraded non-fertilised pasture presented the lowest above ground herbage biomass as well as negative effects on soil physical properties (e.g. Pc increased by 57% and lower physical resilience) after grazing events.