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

The effects of pastoral hill country natural landscape features and land management practices on nitrate losses and its potential attenuation for improved water quality

“…For instance, Crofoot et al (2010) found higher nitrate-N leaching at low (0-12°) and medium (13-25°) slopes compared with high (>25°) slope in a hill country farm in the Wairarapa region of NZ. Similarly, consistent with the higher soil nitrification potential observed at low slopes (Devantier et al, 2012;Letica et al, 2006), Hoogendoorn et al (2016) reported greater nitrate-N leaching on low (68 kg ha −1 ) versus medium (5 kg ha −1 ) slopes at Ballantrae Research Farm in NZ. The authors, however, did not observe differences in the amount of DOC leached from these slope classes.…”

“…Grazing animals tend to graze and rest (camp) on lower slopes than on steeper slopes. This results in the nonhomogeneous distribution of urine and dung along the catena, with a reduction in nutrient accumulation as slope increases (Letica et al, 2006; Saggar et al, 1999). The accumulation of nutrients, runoff and seepage water on flat (low) slopes makes them CSAs with greater potential for nitrate leaching, due to their accumulation and rapid transport processes.…”

“…However, several factors, including grazing management, potentially influence DOC leaching under such fertiliser combinations (Parfitt et al, 2009; Scott et al, 2015). Research on Ballantrae and another hill country farm at Invermay, NZ (Letica et al, 2006) indicated that lower slope areas (camp sites) and soils with high pH (>6) have greater nitrification potential and a higher tendency for nitrate loss following N fertiliser application. This highlights the interaction between landscape features and land management practices that influence potential nitrate leaching loss from the soil profile.…”

Heterogeneity of nitrification potentials within a paddock of a sheep farming system

“…Similar to the current study, a previous study performed at a hill grasslands with Brown soil reported that the nitrification potential was 0.94–1.15 mg N kg −1 h −1 at its animal camping zone, which was >3‐fold higher than other area (Letica et al . ). Le Roux et al .…”