Simulating The Impacts Of Manure Management On CH₄and N₂O Emissions From Dairy Open-lot Surface

Global warming is one of the most challenging concerns of various environmentalissues nowadays. Of the important greenhouse gases, methane and N2O accounted for32%and6%of the global warming due to their high global warming potentials (e.g.25for CH4and298for N2O). It has been indicated that agricultural sectors are the major source ofatmospheric greenhouse gases, whereas the agricultural emissions of methane and N2Owere dominated by the emissions from enteric fermentation and manure storage in animalproduction. In China, feedlot operations are a very common practice due to its inexpensivefacility. In this case, understanding the impact of the type of animal feedlot surfaces as wellas the management practices on methane and N2O emissions is very important to reducethe uncertainty associated with the greenhouse gas inventories and evaluate the usefulnessof mitigation practices.Spatio-temporal heterogeneity of gas emissions from animal feedlot surfaces isconsidered the major barrier in estimating emission rates. Simulations that evaluate theimpact of the existence of consolidated manure pad (CMP) of feedlot surface (i.e.long-term (CMP) vs new (non-CMP) feedlot surface), frequency of dung deposition andremoval as well as DCD (Dicyandiamide) application on CH4and N2O emissions fromdung patches with intact soil core technique were conducted to reveal such heterogeneitymagnitude. Continuous dung deposition turned the non-CMP surfaces from minor CH4sinks to significant sources (2.450mg m-2h-1) and largely increased the CH4emissionsfrom CMP surfaces up to49.485mg m-2h-1with a factor of25-62; it increased the N2Oemissions from non-CMP surfaces over a factor of190yet reduced the N2O emissionsfrom CMP surfaces with a factor of77-103. Average CH4emission rate of the CMPsurfaces was about10times greater than the non-CMP surfaces under both high and lowdung deposition frequency scenarios.For the non-CMP surfaces, CH4emission patterns differed among two depositionscenarios, where under the high frequency deposition, methane rate of non-cmp surfaceincreased continuously from1.75mg m-2h-1to292.8mg m-2h-1, and it sharply declined to20.11mg m-2h-1due to the dung removal event; afterwards, the emission rate build upagain with dung deposition; whereas for the low frequency scenario, the patterns of CH4emissions were consistent with manure deposition events, that is, methane emissionincreased after dung deposition till next deposition event. However, such difference in CH4emissions of the CMP surfaces under two deposition scenarios was less apparent althoughthe impact of manure removal on emissions can be clearly identified.Dung deposition increased the methane emission rates of both CMP and non-CMP feedlot surfaces. However, it differed on N2O emissions, where dung deposition increasedthe N2O emission from non-CMP surface but decreased the emission from CMP surface.In addition, applying DCD decreased the N2O emissions from CMP surface from9.97mg m-2h-1to0.01mg m-2h-1, and the inhibitory effect lasted about65days. However, theinhibitory effect on N2O emissions from other scenarios was not observed, which mightinfer that the inhibitory effect of DCD may only apply for high N2O emission conditions.