Nitrification in pastures on the Northern Tablelands of NSW

An incubation experiment assessed the effects of pasture management and soil depth on nitrification in grazing land on the Northern Tablelands of NSW. Soils from six paired sites, each comprising a paddock of exotic pasture amended with superphosphate and an adjacent roadside reserve of unfertilized pasture, were used in the experiment. Soil samples to a depth of 20 cm were amended with 6 mL of ammonium sulphate ((NH₄)₂SO₄) at the rate of 100mg of NH₄+-N / kg or 6 mL of deionized water and incubated for 24 days at 25°C. Results from one of the sites are reported. It was found that nitrification in the paddock was significantly higher than the reserve and consistent with pasture management that provided ideal conditions for nitrifying bacteria and greater microbial activity. Nitrate concentrations decreased with increased depth for the paddock, yet nitrification, net accumulation of nitrate, did not decrease with depth.