REVEGETATION IN SEMIARID ZONES - INFLUENCE OF TERRACING AND ORGANIC REFUSE ON MICROBIAL ACTIVITY

Revegetation of areas under semiarid conditions is difficult due to bo th the water shortage and the poor quality of the soils of semiarid ar eas; Two techniques of soil management (manually and mechanically buil t terraces), as well as soil amendment with organic materials were use d for revegetation in a semiarid area. In this work the effect of such techniques on the microbial activity of a soil revegetated with Alepp o pine (Pinus halepensis Miller) was studied. The content of the diffe rent labile C fractions studied (water-soluble C, water-soluble carboh ydrates, and polyphenol compounds) substantially increased in soils wi th mechanically built terraces and with addition of organic refuse. Th e highest values of these labile C fractions were found in soil sample s collected in spring (rainy season) while those collected in January (dry season) showed the lowest values. The activity of oxidoreductases such as dehydrogenases as well as that of hydrolases involved in the biogeochemical cycles of important nutrients (ureases, proteases, phos phatases, and beta-glucosidases) were stimulated by the addition of or ganic matter to the soil. The lowest values of microbial biomass and e nzyme activities were detected when revegetation was carried out on me chanical terraces without addition of organic materials. The simultane ous use of both soil management techniques, mechanical terracing and a mendment with organic refuse, clearly improved soil microbial activity and hence soil biological quality. Plant growth was also improved wit h these techniques.