Characterizing CH₄and N₂O Emissions From Intensive Dairy Operations

The emissions of methane and nitrous oxide from livestock farming are the mainsources of global greenhouse gas (GHG) production. It is mainly from the ruminant entericfermentation, manure management systems and following field application. The FAOstatistical report indicated that the total emissions of dairy operations in2004in Chinawere0.57Mt and0.01Mt, account for about4.50%and1.70%of the ruminants emissions.In addition, manure storage is also considered one of the most important sources of GHGin livestock farming, and the emissions of CH4and N2O from manure systems of dairyoperations were0.08Mt and0.01Mt, respectively. These figures are approximately0.50%and0.30%of the global manure methane and nitrous oxide emissions. Therefore,characterizing daily emission patterns of CH4and N2O at farm scale, estimating theiremission intensities based on their milk production and verifying the adaptation of IPCCTier2in the North China will help establish the GHG inventory of China and screenpotential mitigation measures as well.In this study, an inverse dispersion technique and a self-designed automatic samplingdevice were used to quantify methane and nitrous oxide emissions from intensive dairyfeedlots in Northern China in order to investigate diurnal emission patterns of CH4andN2O and thus estimated their emission intensities and conversion factor accordingly. Themain results are in below:1. The daily curves of the CH4emission rates were characterized by apparentemission peaks. At experimental site1, for the milking cows, methane emission peaksstarted at05:30am,11:30am and19:30pm, respectively; for the heifers, the peaks beganat approximately5:30am,10:30am and20:30pm, respectively and05:30am,12:00amand18:00pm at experimental site2; each emission peak lasted about2h. The diurnalpatterns of CH4emissions generally corresponded with the feeding schedule.2. Obvious diurnal pattern of N2O emissions were identified. At these twoexperimental sites, the daily curves of the N2O emissions tended to be lower during the lateevening to early morning and then increased until the late afternoon. The diurnal patternswere related to air temperature and animal activities.3. Emission rates of CH4and N2O for different herds were obtained. At experimentalsite1, the milking cows and heifers were separately managed in different feedlots. Thedaily CH4emission rates for the milking cows and heifers were397g/head/d and279g/head/d, indicating emissions of milking cows approximately42%greater than heifers.The daily N2O emission rates for the milking cows and heifers were37g/head/d and24g/head/d, respectively, where the emissions of milking cows are about54%higher thanheifers, indicating the difference of emissions between different herds.4. In this study, further calculations were performed to obtain the CH4and N2Oemission intensities based on milk production to evaluate the CH4and N2O emissions fromthese two experimental sites. The emission intensities of CH4and N2O in terms of milk production for the experimental site1were23.63L and0.85L, respectively. However, atthe experimental site2, which milking and heifers were managed in the same feedlots, theemission intensities of CH4and N2O were25.50L and0.89L, respectively.5. In addition, methane and nitrous oxide conversion factor of feeds used on these twoexperimental dairy operations during measurements were also calculated using IPCC Tier2methodology. At the experimental site1, the methane conversion factors for milking andheifers were5.17%and7.68%, respectively, and the conversion factors of nitrous oxidewere4.25%and6.86%. However, the conversion factors of methane and nitrous oxide forthe experimental site2were6.20%and5.76%. Through this study, the initial range ofmethane and nitrous oxide conversion factors with intensive dairy feedlot waspreliminarily established.