LAUSR

ABSTRACT Three sites were selected for the present study: native forest (FR), an agricultural land subjected to minimum water erosion by terracing farming (ARMN), and an agricultural land subjected to moderate water erosion without terracing farming (ARMD). Conversion of forest to agricultural land significantly affected soil physicochemical properties. The lowest contents of both humic and fulvic acids were registered in the ARMD site, while the highest was observed in FR. The site with moderate water erosion showed a decrease of total microbial activity as estimated by fluorescein diacetate activity (FDA), but an increase of dehydrogenase activity. Both C-related enzyme activities glucuronidase and glucosidase as estimated by fluorogenic methylumbelliferil (MUF)-substrates were also reduced in ARMD, with moderate values in ARMN site, and high values in FR. Our study revealed that ARMD had the mean microbial biomass estimated by phospholipid fatty acid (PLFA) profiles. Furthermore, the ARMD site showed the highest Gram-positive to Gram-negative ratio, suggesting that moderate water erosion may also affect soil microbial community structure. The results of the present research have important implications for the study of deforestation under sites subjected to water erosion, which is one of the most significant ecological changes facing in central Argentina and the world.