Dynamics of soil nitrogen and water in a selective thinning in the argentinian dry chaco

Resumo

Clearcutting for livestock production in the Dry Chaco is leading to shrub 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 moisture dynamics were studied during one year. Accumulated N mineralization was 40% higher in the selective thinning than in the natural woodland (85% arbustive + tree canopy cover). Different patterns were observed under the dominant tree species. In the selective thinning, available N, N immobilized in microbial biomass and soil water content were significantly higher under Aspidosperma quebracho-blanco Schlecht., Apocinaceae. In the natural woodland, N availability and nitrifier densities were higher under Prosopis flexuosa DC, Fabaceae. The open interspaces between trees exhibited the lowest values of all measured parameters. Possible explanations of observed differences and implications for pasture production are discussed.