Spatial distribution and rate of potential nitrification activity in two hill country pastures

Abstract

The purpose of this study was to conduct a preliminary investigation into the effect of increasing fertiliser- and excreta-N inputs on the spatial distribution and rate of potential nitrification activity in hill country pasture land at two sites, Invermay and Ballantrae. High nitrification rates could potentially limit N efficiency by increasing N losses through leaching and denitrification. Nitrification potentials (NP) were measured in camp sites and medium slopes of hill country soils receiving 0 kg N and 500 kg N/ha/yr over the previous 18 months. Nitrification potential was determined by calculating the rate of nitrate production (mg NO3-N/kg soil/h) by linear regression of soil solution concentrations, versus time. Nitrification potential was significantly higher at Invermay than at Ballantrae, which was likely due to a significantly lower soil pH at Ballantrae. At Invermay, NP increased with fertiliser-N application rate and in camp site soils. The fertiliser N effect was not observed at Ballantrae. However, soil NO3-N and NP was significantly greater in soils from camp sites than for soils from medium slopes. Best management practices for fertiliser-N application in hill country should make allowances for these factors to maximise farm efficiency and profitability. Keywords: hill country, nitrification potential, nitrogen fertiliser, stock behaviour, excreta-N, mineral-N, New Zealand