Felipe Zúñiga

Short-term effects of different pasture improvement treatments on the physical quality of an andisol

Abstract The improvement of degraded pastures is important for increasing pasture herbage mass and animal production in southern Chile. While research has normally focused on how animal treading affects soil compaction, no major work has yet been done to define the impact of pasture improvement managements on soil physical functions, particularly when the initial situation is a degraded pasture. Thus, the aim of this study is to define the short-term effects of different pasture improvement managements on the physical quality and related processes of a volcanic ash soil. Four treatments were defined: two tilled, fertilized and seeded plots (T1 and T2), one non-tilled and non-fertilized plot (T3) and one non-tilled and fertilized plot (T4), all of which were compared to the initial situation of a highly degraded pasture (IS). Undisturbed soil samples were collected (1-10 cm) and the volumetric water content and temperature was continuously monitored at the 10 cm depth. The short-term effects of pasture improvement managements on soil physical quality and related processes differed in relation to the treatment method. As compared to the non-tilled plots, the aggregate destruction after tillage induced an increase in the water holding capacity, but a decrease in the air capacity and pore-continuity values due to grazing. The physical quality assessed by the S-Index reflected a good soil structural quality (S > 0.035). The tilled plots presented a higher S-Index as compared to the non-tilled plots, which is related to a slightly lower mechanical strength and larger water holding capacity. The latter also increased due to tillage and was positively correlated to pasture yields during the first intensive soil drying. Soil temperature differences between treatments were assessed and can be related to the higher water contents in the tilled plots and the presence of broad-leaf species in the non-tilled pastures. Finally, in order to properly understand how the implementation of pasture improvement managements affects the soil physical quality and related processes, long-term studies are required.

Water and temperature dynamics of Aquands under different uses in southern Chile

Aquands are soils derived from holocenic volcanic ashes located in southern Chile. Due to the presence of very high levels of organic matter (30 %), these soils present a high total porosity (80 %) but at the same time, a limited water storage capacity due to their shallow soil depths. The aim of this work was to analyze the influence of land use change of a Duric Histic Placaquand (Nadi) soil on soil physical properties and their consequences on water and temperature dynamics. The volumetric water content (qField) and soil temperature (T) were registered at different depths in a Nadi soil under a secondary native forest (sNF) and naturalized grassland (NG). Undisturbed soil samples were collected to analyze the water retention curve, saturated (Ks) and unsaturated (Ku) hydraulic conductivity and water repellency. The dynamics of rainfall and water table depth (WT) were registered using a rain gauge and groundwater wells. The land use change of a Nadi soil from sNF to NG induced soil structural changes in the first 15 cm of soil reducing the amount of macropores under NG and affecting the hydraulic conductivity function as well as qField and T dynamics, i.e. while the WT in winter reached the soil surface in the NG, under sNF the air-filled pores were still present. Similarly, the T gradients increased as qField decreased, being more intensive under NG. A nonhomogeneous soil wetting and water infiltration was assessed, which can be related to an increased spatial water repellency, soil hydraulic properties and rainfalls.