NITROGEN RUNOFF AND LEACHING LOSSES IN BEEF PRODUCTION SYSTEMS UNDER TWO DIFFERENT STOCKING RATES IN SOUTHERN CHILE. The Lakes Region of Chile produces 60% of the country's milk and 45% of its meat. Production is expected to increase in the near future, yet there are few data on the environmental impact of local livestock systems. A field experiment was carried out during 2004 to measure nitrogen (N) runoff and leaching losses in beef cattle-grazing production systems near Osorno. Grazing was carried out with Holstein-Friesian steers of 220 kg of initial live weight, with stocking rates of 3.5 and 5 steers ha-1. Water samples were collected during 6.5 months with surface lysimeters and ceramic cups, and were analyzed for nitrate and ammonium. Total losses were calculated as the product of N concentration and accumulated drainage at each sampling date. A significant difference in the total N loss was found between the two treatments (11.1 and 29.9 kg N ha-1, respectively; P < 0.05). The main pathway of N loss was leaching, which contributed 99% of the total N loss. Nitrate was the main form of N loss in runoff (71%) and leaching (99%). Average nitrate concentration in leaching samples was always below the European Community Directive limit. However, nitrate concentration in runoff samples had maximum values of 116 ± 13.8 and 82 ± 22.4 mg L-1 for the 3.5 and 5 steers ha-1 treatments, respectively. For the experimental conditions tested, N losses from beef cattle production systems were low. This was related to the low N inputs in fertilizers used and to the physical and chemical properties of the volcanic soils. https://bibliotecadigital.infor.cl/handle/20.500.12220/29484