Characterising And Modelling Of Greenhouse Gas Emissions From The Ground Level Of Dairy Open-lot

Open lots are typical feeding operations for dairy cows in China. In such an operation system, large amount of manure kept on the open lots, and it becomes an important greenhouse gas (GHG) emission source in dairy farm. Due to the difficulties on gaseous emission measurement, little fundamental information can be found on GHG emissions from the dairy open lots in China. This make it impossible to do accurate estimation of GHG emissions from dairy sector and unable to develop targeted strategies for mitigation. Thus, this research choose the most widely used chamber technique as a potential flux measuring method for the open lots, and investigated the impacts of key factors on its measuring accuracy. Using the improved closed chamber, field measurements had been done to quantify the GHG emissions from the brick-paved dairy open lots and manure stockpiles in four consecutive seasons. GHG and ammonia emissions from the open lots were simulated at a lab scale to analyze their emission behavior and the influence of key factors driving gaseous emission. Furthermore, estimation models on CH4 emitted from the ground level of open-lot with unpaved soil floor were established in this study. The results in this study concluded that:(1) Measred fluxes by closed chambers were significantly related to the reference fluxes at a relatively low emission rates. However, closed chambers would underestimated the reference fluxes, and the underestimation decreased at the higher flux level. For a solid emission source, chamber enclosure area didn’t affect the chamber performance (P>0.05) while the height significantly impacted their measurement accuracy (P<0.05). When the headspace air was internally circulated and the vent was closed, with or without the mixing fan and the different fan speed did not affect the chamber performance (P>0.05). However, the mixing fan was found to induce a positive air pressure in chamber headspace. When the vent is open, the mixing fan resulted to an extra positive air pressure and decreased the measuring accuracy of closed chamber. Internally air circulation was recommended to mix the air in headspace.(2) When the manure was collected once a day during field measurements, annual CO2, CH4 and N2O emissions from the ground level of the brick-paved dairy open lots were 137.5±64.7、 0.45±0.21�'�0.13±0.08 kg·hd-1·yr-1, respectively. There were remarkable location variations of GHG emissions from different zones (cubicle zone vs. aisle zone) of the surveyed open lot due to the amount of manure kept on the floor surface. Cubicle zone had higher gaseouse emission (P<0.05). After manure collection, lower CH4 but higher N2O emitted from the open lot (P<0.05). Rainfall could stimulate the N2O emission from the open-lot. Showing a seasonal variation, annual CO2, CH4 and N2O emissions from the uncovered stockpile were 858.9±64.7、 8.5±5.4 and 2.3±1.1 kg·hd-1·yr-1, respectively. CH4 and N2O emissions from the whole manure management system were 9.0 kg·hd-1·yr-1 and 2.75 kg·hd-1·yr-1.(3) Generally, CO2, CH4, N2O and NH3 emissions from the scale model of dairy open lot were significantly enhanced with the increased air temperature and surface velocity (P<0.05). CO2, N2O and NH3 emissions were more sensitive to the air temperature changes from 15℃ to 25℃, while the CH4 emissions were more sensitive to the changes from 25℃to 35℃. NH3 emissions were more sensitive to lower velocity changes.(4) Brick paved floor had higher CO2 and NH3 emissions before manure scraped (P<0.05), while statistical analysis showed no significant difference on CH4 and N2O emissions from different floor types (P>0.05). Due to infiltration, unpaved soil floor lowered CH4 and N2O emissions before manure scraped but highered their emissions after manure scraped, resulted to a secondary gaseous emission.(5) Manure temperature on the open lots was found to be as a function of the air temperature. Air temperature could be used to estiomate the manure temperature on the open lots when it’s unavailable, and the average error was about 2%. CH4 emission from the scale model was exponentially related to CO2 flux (P<0.05). Relationship between surface velocity and CH4 emissions from the unpaved soil floor was more likely to be exponential (P<0.05).