Biological and biochemical quality of a semiarid soil after induced devegetation

Devegetation of soils in arid areas leads to the diminution of their biological quality. In this paper the changes in the biological quality of arid soils due to devegetation have been quantified. The field experiment was carried out on soils from an arid area (southeast Spain) 7 yr after the area was devegetated; this area was contrasted with a natural or undisturbed area. Different parameters related with organic matter as well as biomass C and oxidoreductase and hydrolase activities were determined. Total organic C levels in soils after devegetation fell more than humic substance fractions, among which the most recalcitrant (humic acids) showed the least change. The level of the humic substances 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 activity) and catalase activity. Hydrolases involved in the N cycle (urease), P cycle (phosphatase), and C cycle (beta-glucosidase) became less active, while the protease that hydrolyzes N-alpha-benzoyl-L-argininamide showed no change. There was very little seasonal variation in the activity of the hydrolases analyzed in the area after devegetation.