3. RESULTS
3.1 Description and location of sampling units
Figure 2 shows the study site and SUs locations where soil specimens were extracted. Six dominant land uses were identified in the study area: páramo grasslands – low slope (Ls), páramo grasslands – steep slope (Ss), páramo – dense shrublands (Ds); and agricultural use: fallow (F), spring onion crops (Oc), and potato crops (Pc). Table 2 summarizes the main characteristics of the dominant land uses studied.
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3.2 Influence of seasonality on the soil hydrophysical properties of páramos
Tables 3 and 4 show the influence of the rainfall regime on the soil hydrophysical properties in the SUs under natural vegetation and agricultural use, respectively. It is observed that natural vegetation did not show significant statistical differences on the soil properties between seasons, except for Bd in Ls for the three studied depths (Table 3). This low variability in the hydrophysical properties in the SUs under natural vegetation possibly occurs because natural vegetation protects the soil from the extreme climatic conditions of the páramo, such as high solar radiation, low temperature, strong winds, and high variation in daily temperature (Hedberg & Hedberg, 1979). Likewise, natural vegetation has adapted to capture a large amount of water from rain, dew and mist, store water, minimize water losses by evapotranspiration (Salamanca, 1986), and to trap and accumulate organic matter in its structure (Josse et al., 2009). These two natural processes (water and organic matter storage) interact with each other to maintain regular soil hydrophysical properties despite seasonality changes, supporting their high capacity to store and sustain water fluxes.
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On the other hand, in anthropic SUs, statistically significant differences were observed for SOM and Bd (Table 4). SOM showed statistically significant differences in F at surface level between seasons. An average maximum difference in SOM of 7.2% was observed in F, in contrast with the 2.1% in Oc and -3.2% in Pc (p>0.05) when comparing average values for the wet and the dry season. The low variability in SOM observed in Oc could be associated to the frequent organic fertilization over this SU (every three months with unstable poultry manure), which does not occur in the other agricultural SUs.
Bd had statistically significant differences in Oc and Pc in the whole profile (0–25 cm), with smaller values in the dry season. Ploughing carried out in these plots could change soil structure, degrading macro and micro porosity, which can have different water saturation levels in the soil between seasons, influencing Bd values. In Oc and Pc an average difference of up to 0.21 g cm-3 can be associated to rainfall seasonality, similar to the results reported by Ordoñez, Galicia, Figueroa, Bravo, & Peña (2015) who found differences of up to 0.14 g cm-3. F did not show statistically significant differences, possibly due to the high compaction (i.e., high Bd) in this SU.
pH and EC were not different between wet and dry seasons (p<0.05) in any of the SUs (Tables 3 and 5). A slight reduction in these two properties was observed during the dry season, possibly because of the leaching of soluble ions (Juan et al., 2011) that can decrease pH and EC.
3.3 Influence of agriculture on the soil hydrophysical properties of páramos
This section describes the studied soil hydrophysical properties according to the SUs and depth (0–5, 10–15 and 20–25 cm). Furthermore, the changes on the hydrophysical properties associated to the agricultural land uses (F, Oc, Pc) are analyzed and compared with natural vegetation covers (Ls, Ss, Ds).