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Dissolved organic nitrogen as an indicator of livestock impacts on soil biochemical quality

Nikolaidis Nikolaos, Stamati Foteini, Venieri Danai, Psyllaki Eleftheria, Kalogerakis Nikos

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Summary

Soil degradation in the Mediterranean and other arid and semi-arid regions of the world is caused mainly by cultivation and grazing (Li et al., 2007). Livestock grazing alone is responsible for 23 % of soil degradation in Europe (RCEP, 1996) and is particularly intense in the Mediterranean region. Free grazing of uncontrolled length and frequency and high stocking densities are responsible for the de-vegetation of many areas within this region. The Greek island of Crete represents a characteristic case of land degradation resulting from intensive grazing (Hill et al., 1998). Since Greece joined the European Communities in 1981, grazing in mountainous regions has expanded due to subsidies that became available through the Common Agricultural Policy (Hill et al., 1998). A consequence of de-vegetation due to overgrazing has been a decrease in organic matter (litter) input to soil and a decrease of aggregate size and stability making soils more susceptible to erosion and to organic matter losses (Bastida et al., 2006). DON has been found to be decoupled from the production of DOC in such soils and has proportionally more labile soluble organic matter (Ghani et al., 2007). However, detailed information on the nature, bioavailability, and fate of the mobilized dissolved OM following a change in land use such as de-vegetation is still lacking (Akagi and Zsolnay, 2008).Mediterranean watersheds appear to export a larger fraction of nitrogen in organic form compared to watersheds of continental Europe and North America. However, no systematic analysis of existing data has been made to date. The objective of this work was to test the hypothesis that livestock grazing (and the resulting de-vegetation) degrades soil quality and enriches surface and ground waters with DON by examining data from 3 different scales.

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