Year: 2017
Type: dissertation
Abstract: Globally agriculture and livestock producers have come under increasing pressure over the \nenvironmental impact of production systems. The objectives of this study were to re-calculate the \ndirect methane (CH4) and nitrous oxide (N2O) emissions of livestock production systems in South \nAfrica, taking into consideration the uniqueness of the South African scenario and to identify and \nevaluate possible greenhouse gas mitigation strategies for extensive production systems. It is \nimportant to generate accurate greenhouse gas (GHG) baseline figures to develop South Africa’s \ncapacity to understand and reduce GHG emissions emitted from the livestock sector. \nLivestock produce GHG’s in the form of methane from enteric fermentation and nitrous oxide and \nmethane from manure management and manure deposited on pastures and rangeland by grazing \nanimals. Agriculture, forestry and land use (corrected for carbon sink values) emitted an estimated \n4.9% of South African GHG gases in 2004, which makes it the third largest GHG contributor in \nSouth Africa after the energy industry and industrial processes. Livestock produced approximately \n27% of the national methane emissions and 98% of the agricultural sector’s methane emissions in \n2004. \nMethane is a potent GHG that remains in the atmosphere for approximately 9 to 15 years and is 28 \ntimes more effective in trapping heat in the atmosphere than carbon dioxide (CO2) over a 100-year \nperiod. Nitrous oxide has an atmospheric lifetime of 150 years and a global warming potential of \n265 times that of CO2 over a 100-year period. South African livestock production is based on a unique combination of commercial (intensive and \nextensive) and emerging and communal (subsistence) production systems. The levels of productivity \nand efficiency in these production systems vary greatly in certain areas and it is important to \ndistinguish between them when calculating GHG emissions. Previous inventories were conducted \non a national scale utilizing IPCC default values (Tier 1 approach) for some or all of the emission \ncalculations. These emission factors do not distinguish effectively between classes of animals, \nproduction efficiencies, and production systems. They are often based on assumptions of animals \nutilizing diets which are not representative of South African production systems. \nThe IPCC Tier 2 methodology seeks to define animals, animal productivity, diet quality and \nmanagement circumstances to support a more accurate estimate of feed intake for use in estimating \nmethane production from enteric fermentation. It was also considered important to do separate \ncalculations for each province as provinces differ in vegetation or biomes and production systems \nwhich may require different approaches to mitigation recommendations. Due to the heterogeneity \nof available feed types within South Africa it was considered important to use methodologies that \ncould reflect such differences and was developed under similar conditions. \nThe methodology utilized is based on the Australian national greenhouse account’s National \nInventory Report, which contains Australian country-specific and IPCC default methodologies and \nemission factors. Emission factors specific to South African conditions and management systems \nwere calculated where possible. A Tier 2 approach was adopted for all major livestock categories \nincluding privately owned game in accordance with the IPCC Good Practice requirements. Recently \ngame farming has become a recognized commercial enterprise in the agricultural sector which needs \nto be included as an anthropogenic emissions source. \nMethane emissions from South African livestock were estimated at 1328 Giga gram (Gg) during \n2010. Dairy and beef cattle contributed an estimated 964 Gg or 72.6% of the total livestock methane \nemissions in South Africa during 2010. Beef cattle in extensive systems were the largest contributor \n(83.3%), followed by dairy cattle (13.5%), and feedlot cattle (3.2%). The estimated direct enteric \nmethane emission factors for dairy and beef cattle were higher than the IPCC default factors for \nAfrica. The Eastern Cape recorded the highest dairy and beef cattle methane emissions, whereas \nGauteng showed the highest feedlot methane emissions primarily due to cattle numbers. \nSmall stock was responsible for 15.6% of the total livestock emissions contributing an estimated \n207.7 Gg, with sheep producing 167 Gg and goats producing 40.7 Gg. Calculated enteric methane \nemission factors for both commercial and communal sheep were higher than the IPCC default values \nfor developing countries. A similar tendency was found with goat emission factors. The highest \nsheep and goat methane emissions were reported for the Eastern Cape province. \nThe pig and ostrich industry both contributed approximately 8 Gg CH4 during 2010. The North- \nWest province produced the highest commercial pig GHG emissions with the highest communal pig \nemissions originating from the Eastern Cape. The poultry industry was the largest direct N2O \nproducer of the non-ruminant livestock industries, contributing 2.3 Gg or 92.8% of the total nonruminant \nN2O emissions. \nThe privately owned game industry contributed an estimated 131.9 Gg of methane emissions with \nthe provinces of Limpopo, Eastern Cape and Northern Cape being the three largest contributors with \n43.4, 37.3 and 21 Gg methane, respectively. The total privately owned game population was \nestimated at 2 991 370 animals, utilizing 20.5 million hectares. \nBeef cattle are the major contributors to livestock GHG emissions in South Africa followed by \nsheep, privately owned game, dairy cattle, goats, pigs, ostriches, equine, and poultry. The IPCC \ndefault values for Africa underestimate emission factors across all livestock categories. The methane emission factors calculated for commercial livestock production systems are more comparable to \nemission factors from developed countries and the emerging/communal production systems to those \nof developing countries. This emphasizes the need to develop country-specific emission factors \nthrough quantitative research for livestock in all provinces and on all types of production systems to \nproduce accurate baseline figures, which is critical to future mitigation protocols. \nAs part of this study fourteen tropical grass species typical of transitional rangeland regions of South \nAfrica were characterised in terms of chemical composition, in vitro total gas and in vitro methane \nproduction. The results of the study demonstrated that in vitro methane production varied between \ntropical grass species typical of transitional rangeland in South Africa. The variation between species \nallows for the potential to identify and select species with a lower enteric methane production \npotential. Panicum maximum, Eragrostis curvula and Elionurus miticus were the three species \nwhich produced the lowest in vitro methane production but which also had a crude protein (CP) \nconcentration of more than 3.5% of dry matter (DM) and with an in vitro organic matter digestibility \n(IVOMD) above the group average for the study. Furthermore, the results of the study revealed that \nin vitro methane production was higher in Decreaser species compared to Increaser species. \nImproving the quality of available forages through the use of cultivated pastures and fertilization is \nknown to improve ruminant production efficiency. The effect of level of nitrogen (N) fertilization \non certain qualitative parameters and in vitro total gas and methane production of improved grass \nspecies commonly utilised in South Africa was evaluated. Treatments included seven grass species \ndivided into two photosynthetic pathways (C3 and C4) with three levels of N fertilization (0, 50 and \n100 kg N/ha). No effect was found for N fertilization on in vitro total gas or methane production. \nThe CP concentration increased (P < 0.05) and the NDF concentration tended to decrease (P < 0.1) \nas the level of N fertilization increased for both C3 and C4 species. Increasing the level of N fertiliser \nincreased (P < 0.05) the methanogenic potential of Dactylis glomorata, Festuca arundinacea and \nCenchrus ciliaris after the 24 hour incubation period but no effects (P>0.05) were found after the \n48 hour incubation period. Results suggests that the stage of physiological development of forages \nmight have a greater influence on the methanogenic potential of forages compared to the effect of \nN fertiliser application.
Authors: Du Toit, Cornelius Jacobus Lindeque
Language: English
Subfield: Animal Science and Zoology
Domain: Life Sciences
SDGs: Climate action, Zero hunger
Open Access status: green
OpenAlex ID: W2770520840