Abstract

ALFARO, Marta et al. Nitrogen, Phosphorus and Potassium Losses in a Grazing System with Different Stocking Rates in a Volcanic Soil. Chilean J. Agric. Res. [online]. 2008, vol.68, n.2, pp. 146-155. ISSN 0718-5839.  doi: 10.4067/S0718-58392008000200004.

In Chile there is little information on nutrient losses in livestock systems. The experiment was carried out between 2004 and 2006. Two stocking rates (3.5 and 5.0 steers ha^-1) were tested under rotational grazing with Black and White Friesian steers on a permanent pasture (67.5 kg N and 40 kg P ha^-1 yr^-1). To quantify surface runoff losses (N, P, K), three surface lysimeters (5 x 5 m) per treatment were established. N and K leaching losses were estimated with ceramic cups. Runoff and leachate samples were individually analyzed for available and total N, reactive (RP) and total P, and K. Dissolved organic N (DON) and organic P (OP) were estimated as the difference between total and available forms. The stocking rate did not increase total N, P and K losses (P > 0.05). Losses in surface runoff were < 0.5 kg N, < 0.05 kg P and < 0.6 kg K ha^-1 yr^-1, respectively, due to the low amount of runoff measured. Nitrogen leaching losses were high (11 up to 71 kg ha^-1 yr^-1) and K leaching losses were low (3 to 5 kg ha^-1 yr^-1). Nitrogen in runoff was mainly lost as DON (50%). Nitrogen leaching losses were mainly as nitrate (70%). Phosphorus was lost as RP (70%). Thus, stocking rates of 5.0 steers ha^-1 are plausible, but fertilizer application should be avoided in rainfall periods during the year to reduce incidental nutrient losses.

Keywords : eutrofication; water quality; grazing; Andisol; beef production.