Figure 1. General map of the study site, the experimental plots, and sampling points. In the upper left and lower right corners of the map, there are zoom layers displaying the four 100 x 100 m plots for each condition (OG and CG fenced area).
In each zone (CG and OG), four plots of 100 x 100 m were randomly established using the Geographic Data Analysis R package (Hijmans & Van Etten, 2016). Then, at each plot, eight random sampling points were selected using the same R package. Once the sampling points were established in the field, in each one of the random plots, we stratified four of these points in a bare soil condition and four under Araucaria canopy to consider the heterogeneity derived from the high clustering of tree coverage in the study area (Figure 1).
In each point, and to consider the spatial variation of the soils (Kirwan et al., 2005), four auger samples per sampling point were composited at two established depths (0 – 15 cm and 15 – 30 cm) (n=128). The samples were collected in sterile and hermetic bags and separated into two aliquots, one for keeping it at four °C for NO3- and NH4+. These were measured colorimetrically within 48h after sampling (Forster, 1995; Miranda et al., 2001). The second larger aliquot was air-dried (25°C) and sieved (<2mm) for later analysis. Total C and N were quantified by Dumbas combustion using a SERCON© EA total CHNS analyzer. Besides, we determined N following the Kjeldahl distillation method (Sadzawka et al., 2006). Total, organic and inorganic phosphorus were determined following the protocol described by Bowman & Moir (1993), using EDTA as the extraction solution. Available phosphorus was measured by the Olsen extraction method adapted by Sadzawka et al. (2006). Permanganate oxidizable carbon (POXC) was determined following the procedure described in Weil et al. (2003) as an index for easily decomposable carbon (Culman et al., 2012). Soil pH was measured with combined electrodes in both 1:1 soil/water and 1:50 NaF suspension. Cation exchange capacity (CEC) was determined following the protocol described in Sadzawka et al. (2006) buffered (pH=7) ammonium acetate as the extractant solution. All these analyses were performed at the Soil, Water, and Forest Research Laboratory of the University of Concepción (http://www.lisab.udec.cl).
For physical parameters, in each sampling point, infiltration tests were conducted using a Mini-Disk infiltrometer (Decagon ©). Also and following the protocol described in Mohanty et al. (1994), a 750cc undisturbed soil sample was taken from the soil surface up to 10 cm depth and carefully transported into the laboratory for soil saturated conductivity measurements (Ksat) using the ”Constant-Head” method (Black et al.,1965). Following the Ksat measurements, the samples were analyzed for soil bulk density, particle density (Blake & Hartge, 1986), texture (Day, 1965), and water holding capacity as described in Burt (2004). Also, undisturbed soil samples were taken at each sampling point from the top 5 soil cm and used to estimate aggregates stability using a wet sieving apparatus (Eijkelkamp ®) following the methodology described by Kemper & Rosenau (1986) and the adaptation described in Rivera & Bonilla (2020) for the Eijkelkamp wet sieving apparatus.