Opportunities to improve sustainability on commercial pasture-based dairy farms by assessing environmental impact

Abstract

For pasture-based dairy farming to become more sustainable, the negative environmental impacts associated with milk production must be minimized. These negative impacts include eutrophication, ammonia emissions and greenhouse gas (GHG) emissions. Two tools, a nutrient budget and a carbon footprint calculator, allow farmlevel assessments of these negative impacts. In this study, a nutrient budget was used to calculate the efficiency of nitrogen and phosphorous use, and a carbon footprint calculator was used to calculate GHG emissions. Farm system descriptors were used to identify the farm systems that had the lowest environmental impact. Soil carbon was measured as an indicator of soil health, and the link between soil health, nutrient use efficiency and GHG emissions was examined. Nitrogen and phosphorous were not efficiently utilized on the farms included in this study, with a large excess of nutrients imported onto the farms each year. The average use efficiency was 29% for nitrogen, and 36% for phosphorous. The GHG emissions per liter of milk production were higher on the farms included in this study than found in previous studies on dairy farms, with an average of 1.39 kg of carbon dioxide equivalents emitted per kilogram of energy-corrected milk. Farm systems which optimized milk production on the available land, while applying the least amount of fertilizer and feeding the least amount of purchased feeds per milk produced, had the lowest environmental impact. Farms with higher soil carbon levels had higher nitrogen use efficiencies and lower GHG emissions. This is the first South African research to examine environmental impact on pasture-based dairy farms in this manner. It is possible for pasture-based dairy farmers to reduce the environmental impact of milk production by adopting some of the principles identified in this study. conserved forage (roughage). The two farm types employ very different practices and mechanisms to reduce environmental impact and improve efficiency, but comparisons between them are few (Scholtz et al., 2013;O'Brien et al., 2014). The two types are also not always operated

Environmental Impact of Rotationally Grazed Pastures at Different Management Intensities in South Africa

“…Methane emissions, as a result of enteric fermentation from dairy cows, ranged between 30% and 65% and comprised the highest contributor to the total GWP in the current study. The N0 and N20 treatment values are comparable to other literature values, which were between 58 and 65% of the total CO 2 eq in the CF of milk in dairy systems [ 6 , 53 , 55 , 56 , 57 ], but were found to be lower for the N60 and N80 treatments. However, most of these values were obtained from intensive confinement systems in which cows had a higher daily DM intake and consequently higher CH 4 emissions per cow and year.…”

“…The calculated CF, from the investigated low-cost grazing system reported here, ranged between 1.3 and 2.6 kg CO 2 eq kg ECM −1 for South Africa ( Table 3 ). These values are higher than studies by Galloway et al (2018) [ 6 ] and Keller et al (2017) [ 51 ], which reported CF values in the range 0.94–2.07 kg CO 2 eq kg ECM −1 and 1.2–2.0 kg CO 2 eq kg raw milk, respectively, from pasture-based dairy systems. However, the CF of the N20 treatment was within this range (1.3 kg CO 2 eq kg ECM −1 ), and this is more representative of the normal management regime and fertilizer guidelines currently followed.…”

“…The performance of pasture-based dairy farms is dependent on herbage yield and its quality. Irrigation and fertilizer can increase herbage yield of pastures and thereby enable increased stocking rate and milk production [ 6 ]. Availability of water is usually a limiting factor due to insufficient precipitation, and therefore pastures in some areas are additionally irrigated.…”

“…Currently in South Africa, only a few attempts have been made towards calculating the CF of milk from pasture-based systems. These studies suggest that the CF of milk ranges from 0.94 to 2.07 at the farm gate, but little is known on the impacts that N fertilizer management has on the CF of milk in South African dairy systems [ 6 , 18 , 19 ].…”

Carbon myopia: The urgent need for integrated social, economic and environmental action in the livestock sector

“…When GHG emissions were allocated between these various purposes, Weiler et al ( 2014 ) found GHG emissions per unit weight of milk from smallholder dairying in Kenya of 2.0 (0.9–4.3) kg CO 2 ‐e using economic allocation to food products only, 1.6 (0.8–2.9) kg CO 2 ‐e when allocation was based on economic functions, and 1.1 (0.5–1.7) kg CO 2 ‐e when emissions allocation considered the livelihood values of livestock. These emissions intensities are comparable to intensive dairy production systems (Alvarez‐Hess et al, 2019 ; Beauchemin et al, 2010 ; Christie et al, 2018 ; Galloway et al, 2018 ), clearly highlighting a need for careful consideration of the diverse economic, environmental and socio‐economic roles that livestock play, particularly in smallholder systems.…”