NH3 emissions from grazing pasture following urea and urease inhibitor treatments

Mei Bai1*, Helen Suter1, Shu Kee Lam1, Rohan Davies2, Deli Chen1

1 Crop and Soil Sciences Section, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Parkville, VIC 3010, Australia

2BASF Australia Ltd., Southbank, VIC 3006, Australia

*Corresponding author: [email protected]

Abstract

Ammonia (NH3) volatilization to the atmosphere following urea based nitrogen (N) fertilizer application not only causes nutrient loss but also detrimentally impacts on the environment, our ecosystems, and contributes to global warming (as an indirect greenhouse gas). Here, we report our studies of quantifying NH3 emissions from dairy pasture following urea application, and the effectiveness of a urease inhibitor in mitigating NH3 loss. Two experiments were conducted in summer at Queensland (northern site) and autumn at South Australia (southern site) where urea was surface applied to pasture. A urease inhibitor (NBPT, applied with urea as Green ureaNVTM) was added at the northern site. Open-path NH3 laser concentration sensors were used to measure line-averaged concentrations along an open path downwind of the treatment plots. Ammonia fluxes were calculated using the inverse-dispersion technique (WindTrax). We found NH3 flux increased following urea application and varied temporally at the two sites. Daily average NH3 flux from dairy pastures fertilized with urea was 4.4 ± 0.46 and 6.4 ± 1.2 mg N m-2 h-1 for the northern and southern sites, respectively. Nitrogen loss as volatilised NH3 from the urea application over the course of the experiments (12-15 days) accounted for approximately 40 and 60% of total applied N for the northern and southern sites, respectively. The difference between sites is likely attributed to the differences in N input, soil properties and microbial activity. The urease inhibitor reduced NH3 emissions by approximately 71% compared to that from the urea treatment. The results in these studies also demonstrated that inverse-dispersion technique combined with the open-path lasers is able to measure NH3 fluxes from large-scale field sites, and the open-path NH3 laser has adequate detection resolution.