SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...
SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...
SCHRIFTENREIHE Institut für Pflanzenernährung und Bodenkunde ...
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grazing for a southern caldenal soil in Argentina. However, we also fo<strong>und</strong> that<br />
soil physical functions had been improved after fenced for a longer period (e.g.,<br />
25 yr in UG 79), as mirrored by a decrease in bulk density accompanied by an<br />
increase of total pore volume. Processes contributing to the natural recovery of<br />
physically degraded soil in the ungrazed sites might include reduction of animal<br />
trampling, earthworm burrowing, root penetration and decay, wetting and drying<br />
cycles, and freezing and thawing cycles (Drewry et al., 2006). Our results<br />
therefore suggests that reduction of grazing intensity could improve soil<br />
functions again, which was in agreement with Proffitt et al. (1995), who fo<strong>und</strong><br />
that natural recovery of soil physical properties <strong>und</strong>er pasture happened<br />
relatively rapid.<br />
106<br />
Grazing influenced hydraulic parameters, i.e., decreasing θs, θr, α, and Ks<br />
due to compaction effects. These grazing-induced changes were parameterized<br />
by the coupled water and heat model HYDRUS-1D. To account for the special<br />
conditions in grazed semi-arid grassland systems we modified root growth<br />
dynamics and bo<strong>und</strong>ary conditions according to the different grazing intensities.<br />
Particularly, three main improvements were <strong>und</strong>erlined. Firstly, we ran root<br />
growth model to reflect dynamics of plant water uptake, which was important<br />
because models designed to simulate agriculture management were normally<br />
limited to simulate crop growing. Secondly, estimate of the intercepted water<br />
provided an accurate bo<strong>und</strong>ary condition. Finally, the ET partitioning, based on<br />
the actual measurements, was essential for the prediction of plant transpiration<br />
since it was only determined by root water extraction function related with<br />
potential transpiration in HYDRUS code.<br />
After the model parameterization, there was a good matching between<br />
measured and simulated soil moisture and temperature at each site. This<br />
indicated that HYDRUS-1D model was suitable tool to reflect the grazing effects<br />
on water and heat fluxes. The LDP model was better than the NN model to<br />
predict the water fluxes as it reflected the soil structural changes affected by soil<br />
compaction. This result was consistent with Richard et al. (2001), who