Greenhouse gas emissions from dung, urine and dairy pond sludge applied to pasture. 1. Nitrous oxide emissions

Abstract

Nitrous oxide (N2O) from excreta deposited by grazing ruminants is a major source of greenhouse gas emissions in Australia. Experiments to measure N2O emissions from dairy cow dung, urine and pond sludge applied to pasture, and the effectiveness of the nitrification inhibitor nitrapyrin in reducing these emissions, were conducted in south-western Victoria, Australia. In Experiment 1, emissions from urine, with and without nitrapyrin, and from dung were measured. Treatments applied in September 2013 resulted in cumulative emissions (245 days) of 0.60, 5.35, 4.15 and 1.02 kg N2O-nitrogen (N)/ha for the nil, urine (1000 kg N/ha), urine (1000 kg N/ha) + nitrapyrin (1 kg active ingredients/ha), and dung (448 kg N/ha) treatments, respectively, giving emission factors of 0.47% and 0.09% for urine and dung respectively. Nitrapyrin reduced N2O emissions from urine for 35 days, with an overall reduction in emissions of 25%. In Experiment 2, sludge, with and without nitrapyrin, was applied in May 2014, and dung was applied in May, August, November 2014 and January 2015. Cumulative emissions (350 days) were 0.19, 0.49, 0.31 and 0.39 kg N2O-N/ha for the nil, sludge (308 kg N/ha), sludge (308 kg N/ha) + nitrapyrin (1 kg active ingredients/ha), and dung (total 604 kg N/ha) treatments, respectively, giving emission factors of 0.10% and 0.03% for sludge and dung. Nitrapyrin reduced N2O emissions from sludge for 60 days, with an overall reduction in emissions of 59%. A third experiment on two soil types compared emissions from urine and dung, with and without nitrapyrin, applied in different seasons of the year. Emissions were highly seasonal and strongly related to soil water status. Emission factors (90 days) ranged from 0.02% to 0.19% for urine and 0.01% to 0.12% for dung. Nitrapyrin reduced emissions from urine by 0–35% and had little effect on emissions from dung. Overall, the experiments found that nitrapyrin was an effective tool in reducing emissions from urine, dung and sludge applied to pasture, but the magnitude varied across the year, with nitrapyrin being most effective when soils had >70% water-filled pore space when major emissions occurred.