NITROGEN EXPORT FROM FORESTED AND AGRICULTURAL WATERSHEDS OF SOUTHERN CHILE

Measuring nutrients fluxes in watersheds with different landuse is important for evaluating the effects of conversion of native forests to agricultural land, and for establishing guidelines for land management. Nitrogen (N) concentrations and fluxes were studied over a 12-month period in four watersheds in the Lake Rupanco basin in the Andean Cordillera and four watersheds located in the Lake Huillinco basin in the Coastal Cordillera of southern Chile. Two watersheds in either lake basins were covered mainly by native rainforests, and the other two had mixed landuse (livestock pastures, subsistence agriculture and shrub-pasture mixtures). In the Lake Rupanco area, the annual transport of NO3-N from forested and agricultural watersheds was 4.9 and 11.0 kg ha-1 yr-1, respectively. Inorganic-N (NO3-N + NH4-N) accounted for 53% and 74% of N transport in forested and agricultural watersheds, respectively. In the Lake Huillinco area, the annual transport of NO3-N was 1.4 and 0.8 kg ha-1 yr-1, respectively, with nitrogen organic forms (DON), prevailing and exported mainly from native forests. The impact of the replacement forests by livestock pasture was clearly reflected in the streamwater NO3-N concentrations and fluxes in the watersheds at the Lake Rupanco basin, probably due to fertilization practices