Nitrogen, Phosphorus and Potassium Losses in a Grazing System with Different Stocking Rates in a Volcanic Soil

Abstract

A B S T R A C TIn 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.

Nutrient retention in a microcatchment with low levels of anthropogenic pollution

“…This means that even though the soils belong to the same Valdivia series, important differences along a transect from upland areas to streambeds were found. We also discovered an unexpected variation in phosphorus retention: the extractable aluminum values above 1,000 mg kg -1 found in both the grasslands and the forested slopes are typical for allophanic soils implicated in high phosphorus retention (Rodríguez et al 2001, Alfaro et al 2008. Generally, the higher Olsen phosphorus concentrations were inversely correlated with extractable aluminum, but grassland avoided this trend.…”

“…variable charge, low bulk density, high hydraulic and air conductivity, among other characteristics (Dörner et al 2009). Furthermore, these soils also have a very high capacity of phosphorus adsorption due to their aluminum and hydrous oxide composition (Alfaro et al 2008). On the other hand, the anthropogenic replacement of upland forests by grasslands should produce a difference in carbon accumulation in soil, which should be more elevated in forests still growing in the floodplains.…”

Intensification of grassland and forage use: driving forces and constraints

“…Intensification of dairy production has been made possible through increased pasture productivity, that is through reseeding, fertiliser applications, rotational grazing and increased pasture utilisation (Alfaro and Salazar 2005;Alfaro et al 2008;Núñez et al 2010). Application of fertiliser P to pastures on the dominant (~90%) low-P volcanic soils has greatly contributed to increased pasture productivity (Escudey et al 2001).…”

“…Although direct P losses have been estimated to be low (<80 g P/ha) (Alfaro and Salazar 2007), there is an increasing risk of surface water pollution when high P inputs continue. Slurries collected during confinement are temporarily stored in open ponds and then surface-applied to pastures (at an N application rate of 40 kg/ha.year; Alfaro et al 2008). Total ammonia (NH 3 ) volatilisation losses from urea fertilisers and cattle slurry are in the range of 20-50% of the amounts of N applied (Salazar et al 2012b).…”

Soil nitrogen contribution to grasslands and its implication for nitrogen use efficiency

“…This has resulted in greater yields and stocking rates being used in direct grazing (Alfaro et al, 2008). Moreover, available data suggest that further intensification of grasslands is still possible (Oenema et al, 2014).…”