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.
[Insert Figure 2]
[Insert Table 2]
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.
[Insert Table 3]
[Insert Table 4]
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).