Fertiliser Formulation Effects on Gross Nitrogen Transformations in Permanent Grassland Soil.

Agriculture was responsible for almost one third of Ireland’s overall Greenhouse Gas (GHG) emissions in 2012, with 39% of these emissions arising from chemical/organic fertilisers in the form of nitrous oxide (N₂O). Ireland has a target to reduce GHG emissions by 20% below 1990 levels by 2020 while increasing the volume of milk produced by 50% in the same timeframe. The contradictory aims of increasing food production while reducing GHG emissions will require an adjustment to the current system of agricultural production. As part of a larger study evaluating the  switching of nitrogen (N) fertiliser formulation to minimise N₂O emissions, (from calcium ammonium nitrate (CAN) to urea based formulations), this experiment examined the effect of urea based fertiliser formulations on gross N transformations in a permanent pasture soil from Hillsborough, Co. Down, Northern Ireland.

 

This study used an established grassland soil in a laboratory incubation study, to examine the effect of urea in various combinations with two types of inhibitors on the soil N dynamics and N₂O and N₂ emissions.  The inhibitors examined were the urease inhibitor N-(butyl) thiophosphoric triamide (nBTPT) and the nitrification inhibitor dicyandiamide (DCD). ¹⁵N isotopic labelling was applied to the samples to allow the determination of several simultaneously occurring gross N transformation rates.  Soil mineral N (urea, NH₄⁺ , NO₂^- and NO₃^-) concentrations, gaseous losses (N₂O and N₂) and the ¹⁵N enrichments of the NH₄⁺, NO₂^-, NO₃^- , N₂O and N₂ were analysed on 8 separate occasions over 25 days. A numerical ¹⁵N tracing model (Müller et al., 2007) was used to quantify gross N transformation rates.  The effect of the inhibitors on gross N transformations, sources of N₂O and N₂O:N_2, emission ratios was analysed.