Effects of surface wind speed and simulated precipitation on N2O emissions in cow manure stacking

Abstract: Through nitrification and denitrification process of nitrogen, nitrous oxide (N2O) could be generated and emitted from animal manure storage, which is catching more attention because of its much higher global warming potential (GWP, 265 times of CO2) and the side effect of ozone destruction. In China, it is documented that N2O emission accounts for approximately 18.23% of its total greenhouse gas (GHGs) production from animal industry in 2015. For dairy operation in Northern China alone, the estimation of N2O production is about 6.24×106 t in 2012. Open lots is a typical operation for keeping dairy cows in China, and the short term storage of the solid dairy manure collected from the barn and lots somewhere inside the farm from days to weeks before land application is a common management in China, which currently result in a large amount GHGs emission to atmosphere, including N2O, CH4 and CO2, making the dairy operation an important contributor to global warming. Except for physicochemical properties of the manure, N2O generation and emission process from the unshielded dairy manure storage is easily affected by ambient temperature, surface wind velocities and natural rainfall, while the emission law is still lacking of relevant explanations. In this paper, laboratory experiment trials was conducted to reveal the effect of different wind velocities (0.5m/s, 0.8m/s, 1.2m/s and 1.6m/s) and simulated rainfall (a total of 9.9 mm) on N2O emissions during the dairy manure storage by using the dynamic chamber technique to simulate the real management practice. Results show there was a significant variation on the N2O emission under different wind velocities with/without simulated rainfall. The N2O emission increased as wind speed increasing in the range of 0.5-1.2 m/s, and the emission reached the peak at 1.2 m/s rather than 1.6 m/s, which could be explained by the crust formation on the surface under the maximum wind speed. The N2O emission after the simulated rainfall sharply increased within an hour and then dropped rapidly to the emission level before-rainfall, and the process lasted for about 10h. The sharp increase could be mainly explained by the destruction of crust formed on manure surface by the simulated rainfall, which theoretically constrained the N2O emitted process, boosted the vitalization of N2O from manure to free air in a short time. Although the simulated rainfall stimulated the N2O emission in the 10h duration, the total GHGs emissions in the days with rainfall were effectively reduced by 12.9% and 10.9% compared with that of the day before because of its influence on CH4 and CO2 emissions. With the implementation of green bill policy in China, more measures to protect animal manure from the natural rainfall are taken in practical management of dairy farms, helping the producers to reduce the GHGs emissions to the atmosphere and the neighbor complaints due to odour annoying.