Methane and nitrous oxide emissions from pen surfaces in a commercial beef feedlot in South Africa

Abstract

The aim of the study was to determine methane (CH4) and nitrous oxide (N2O) emissions from beef feedlot pen surfaces, as influenced by diet and seasons, and from back grounding operations as well as manure management systems across different seasons at a commercial beef feedlot in Mpumalanga, South Africa. The closed static chamber method was used for measuring CH4 and N2O emissions from the feedlot. Feedlot surface parameters such as temperature, pH, moisture, ash, nitrogen (N), neutral detergent fibre (NDF) and acid detergent fibre (ADF) concentrations all observed differences (P<0.05) in set seasons between treatments. Methane and N2O emissions from feedlot pen surfaces were influenced by different feedlot diets fed. Within the feedlot, the grower diet observed the highest overall CH4 and N2O emissions over the measured seasons, whilst the starter treatments observed the lowest CH4 and N2O emissions over the measured seasons. The seasons that experienced, on average, higher CH4 and N2O emissions were the dry and hot season and the wet and hot season, which indicated that temperature and moisture had an effect on CH4 and N2O emissions from manure and feedlot surfaces. Methane and N2O emissions from the manure management practices were affected by season, with the wet and hot season having the highest CH4 emission for both the effluent dam and manure piles, which indicated that available substrate, through rainfall wash off into the dam, and adequate moisture, though rainfall, in the piles allowed favourable conditions for CH4 production to occur. The N2O emissions from the effluent dam were lowest in the wet and hot season and highest in the dry and cold season, whilst for the manure piles it was lowest in the dry and cold season and highest in the wet and hot season. Manure characteristics differed between seasons as a result of different feedlot diets, including rangeland grass and supplement fed. This could have affected the rate of CH4 and N2O emissions from the manure as a result. The gas emissions observed did show a trend between diets fed within the feedlot, with the manure management areas (pile and effluent dams) recording the highest CH4 emissions over each of the measured seasons. The CH4 emissions between seasons within the feedlot and manure management practices, observed significant differences for certain treatments and seasons, as well as certain manure characteristics which observed significant differences. The N2O emissions observed showed no set trend between areas measured on the feedlot. The varying values, and negative values obtained may indicate a general uptake of N by soil or microorganisms (Chantigny et al., 2007; Li et al., 2011). Chadwick et al. (2011) described how farm management decisions interact with environmental controls, such as temperature and water availability to influence key microbial processes, which ultimately affects the magnitude of emissions from each stage of the manure management continuum. In this trial, environmental conditions could have influenced the manure composition at different sites within the feedlot across the different seasons. Although the CH4 and N2O emissions from a commercial beef cattle feedlot in the present trial did differ between seasons, only the grower treatment observed significant differences for CH4 emissions from feedlot pens surfaces. Rangeland observed significant differences between the dry and cold season and dry and hot season as compared to the wet and hot season for both CH4 and N2O emissions. This was different for the manure piles, N2O emissions, which observed no differences (p>0.05) between seasons, and the effluent dam, CH4 emissions, which observed a significant difference between the wet and hot season as compared to the dry and hot season and dry and cold season. The piles CH4 emissions observed a difference between the dry and hot season as compared to both the dry and cold season and wet and hot season. Within the present trial the highest emissions within the feedlot pens were recorded during the dry and hot season for the grower treatment and the dry and cold season for CH4 and N2O respectively. The highest recorded emissions for CH4 in the management systems were in the hot and wet season for both the effluent dam and manure pile system. The highest N2O emissions were observed during the dry and cold and wet and hot seasons for effluent dams and manure piles respectively. The results of the present trial suggests that the difference between the seasons, and manure composition, based on diet fed, impacted on the feedlot pen surface parameters, and ultimate CH4 and N2O production from beef cattle manure.