DYNAMICS OF SOIL-NITROGEN AND WATER IN A SELECTIVE THINNING IN THE ARGENTINEAN DRY CHACO

Clearcutting for livestock production in the Dry Chaco is leading to s hrub invasion and desertification. This trend could be avoided through a more rational management of the arboreous resources. The effects of a selective thinning (40% tree canopy cover) on soil nitrogen and moi sture dynamics were studied during one year. Accumulated N mineralizat ion was 40% higher in the selective thinning than in the natural woodl and (85% arbustive + tree canopy cover). Different patterns were obser ved under the dominant tree species. In the selective thinning, availa ble N, N immobilized in microbial biomass and soil water content were significantly higher under Aspidosperma quebracho-blanco Schlecht., Ap ocinaceae. In the natural woodland, N availability and nitrifier densi ties were higher under Prosopis flexuosa DC, Fabaceae. The open inters paces between trees exhibited the lowest values of all measured parame ters. Possible explanations of observed differences and implications f or pasture production are discussed.