Nitrogen, phosphorus and potassium losses in a grazing system with different stocking rates in a volcanic soil.

A B S T R A C T 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.