Temporal dynamics of the physical quality of an Andisol under a grazing system subjected to different pasture improvement strategies

•We study the physical quality of an Andisol under different pastures.•Capacity and intensity parameters were measured in tilled and no-tilled soils.•The physical properties change depending on the pasture improvement strategies.•Pore functions evolved positively in pastures that maintained their structure.

The south of Chile presents adequate conditions for the development of pastoral ecosystems in volcanic soils. The improvement strategies of these pastures consider soil tillage and fertilization. Andisols have special physical properties, however, their ability to support high stress levels affecting the soil physical quality should be defined. The aim of this study was to evaluate the evolution of the effect of different pasture improvement strategies on the physical quality of an Andisol. The study was carried out in the Estación Experimental Agropecuaria Austral (39°46′ S, 73°13′ W), on a Duric Hapludand. Four treatments were randomly distributed corresponding to a mixed binary species (T1: Lolium perenne L. + Trifolium repens L.), a multiple species mixture (T2: Bromus valdivianus Phil., L. perenne, Dactylis glomerata L. and T. repens) both of which were tilled, and another two that had no mechanical intervention of the soil, which was degraded naturalized pasture without fertilization (T3) and, finally, one that represented a naturalized degraded pasture with fertilization (T4). Additionally, a naturalized, degraded pasture without intervention was analyzed, which corresponded to the initial situation (IS) of the pasture. Undisturbed samples were taken between 1 and 10 cm in December 2010 and October 2011. The bearing capacity of the soil (BC), the water retention curve (WRC), the saturated hydraulic conductivity (Ks) and the air conductivity (kl) were determined. Soil physical quality indicators were derived such as plant available water (PAW), pore continuity indexes (C2 and C3) and the S index for physical quality. The tillage of the soil separated the pastures, grouping them into either disturbed (T1 and T2) or non-disturbed (T3 and T4). In general, parameters that were derived from the pore volume never reached the critical levels (e.g., PAW > 20%, S Index > 0.035) proposed in the literature. On the other hand, parameters that define the functionality of the porous system (kl), showed differences in one order of magnitude between pastures that maintained their structure (T3 and T4) compared to the tilled ones (T1 and T2), so that for T4 the pore continuity index (C2 and C3) increased by 300% and the volume of blocked pores (ϵb) did not reach 1%. At the same time, properties that define the performance of the pores evolved positively over time in a more intense manner in pastures that maintained their structure (T3 and T4). However, this does not mean that in the long term these pastures would not present conditions of physical degradation.