BIOLOGICAL AND BIOCHEMICAL QUALITY OF A SEMIARID SOIL AFTER INDUCED DEVEGETATION

Devegetation of soils in arid areas leads to the diminution of their b iological quality. In this paper the changes in the biological quality of arid soils due to devegetation have been quantified. The field exp eriment was carried out on soils from an arid area (southeast Spain) 7 yr after the area was devegetated; this area was contrasted with a na tural or undisturbed area. Different parameters related with organic m atter as well as biomass C and oxidoreductase and hydrolase activities were determined. Total organic C levels in soils after devegetation f ell more than humic substance fractions, among which the most recalcit rant (humic acids) showed the least change. The level of the humic sub stances was higher in summer. Water soluble compounds, which are used as an energy source by microorganisms, were affected by devegetation, as was dehydrogenase activity (indicative of microbial metabolic activ ity) and catalase activity. Hydrolases involved in the N cycle (urease ), P cycle (phosphatase), and C cycle (beta-glucosidase) became less a ctive, while the protease that hydrolyzes N-alpha-benzoyl-L-argininami de showed no change. There was very little seasonal variation in the a ctivity of the hydrolases analyzed in the area after devegetation.