Influence of enhanced efficiency fertilisation techniques on nitrous oxide emissions and productivity response from urea in a temperate Australian ryegrass pasture

Abstract

The effect of a nitrification inhibitor on nitrous oxide (N2O) emissions across seasons, the effect of a urease inhibitor and a fine particle spray (both targeting ammonia (NH3) loss) on N2O emissions, and the potential for productivity benefits and efficiencies by using these enhanced efficiency fertilisers (EEFs) were investigated in temperate pastures. The study compared three treatments over an eight month period (April to December 2010): (1) urea (U), (2) urea with a nitrification inhibitor (3,4-dimethylpyrazole phosphate) (DMPP), and (3) urea with a urease inhibitor (N-(n-butyl) thiophosphoric triamide (NBTPT)) (GU). In autumn, when NH3 loss was predicted to be high, the effect of urea applied as a fine particle spray (containing urea, NBTPT and gibberellic acid (10g ha–1)) (FPA) on N2O emissions and productivity was determined. N2O emissions from urea applied to pastures were low, and were larger in spring than autumn due to soil moisture and temperature. DMPP was an effective tool for mitigating N2O emissions, decreasing fertiliser-induced N2O emissions relative to urea by 76% over eight months. However, the urease inhibitor (NBTPT) (GU) increased N2O emissions from urea by 153% over eight months. FPA had no impact on N2O, but was only examined during periods of low emission (autumn). No significant biomass productivity, agronomic efficiency benefits, or improvements in apparent fertiliser recovery were observed with the DMPP and GU treatments. A significant biomass productivity benefit was observed with the FPA treatment 55 days after fertiliser was applied, most likely because of the gibberellic acid. The outcomes highlight that although DMPP effectively decreased N2O emissions it had no impact on biomass productivity compared with urea. The use of the GU increased N2O emissions by preserving NH3 in the soil. To avoid this a lower rate of N should be applied with the urease inhibitor.