No abstract

Abstract:Soil moisture patterns were recorded for six different land uses, including oak forest, matorral scrub, olives, and a cultivated field, in central Spain during 1998-99. Volumetric water content was determined using time domain reflectometry at more than 140 sites in each, extending across a range of topographic units. Soil moisture content was a function of land use, with the oak forest being wetter than either the matorral shrubby area or the cultivated site. The spatial patterns for a wet period were kriged and are presented as interpolated contour plots. Geo-statistical analysis confirmed that the patterns were highly heterogeneous, as the variograms showed a pure nugget for each land use, except for the two olive sites, where some spatial structure could be observed. During the investigation the soils were in the dry state and the soil moisture distribution was controlled by 'local' factors; it was not possible to determine which environmental factor had the most influence.

No abstract

No abstract

Soil variability is often seen as problematic in land degradation studies in terms of sampling effort, data interpretation and for the extrapolation of results to other areas or time periods. Examples are given from land degradation research undertaken in central Spain which demonstrate some of these problems associated with soil variability. Geostatistics is presented as a usefu1 tool for quantifying soil variability and in particular the variogram for interpreting and understanding spatial patterns. Soil variability is also seen to complicate the issues surrounding management strategies and makes monospecifi c management strategies less likely to be successful. In recent years several studies have suggested that variability in soil properties and vegetation cover may reduce the risk of land degradation by minimizing the spatial extent of runoff and erosion. These studies suggest that increasing soil variability may prove to be an effective strategy for reducing the runoff and erosion risk. This paper discusses these ideas and highlights the importance of increasing thresholds above which runoff and erosion occurs for the success of such strategies. TIlls in particular applies to many semiarid environments where thresholds are deemed to be extremely low. Finally, these concepts are placed in the context of scale where soil variability may be viewed as existing at a multitude of nested levels varying from the micro-to the macro-scale.