# The Carbon Footprint of Milk Production on a Farm
## 3 Results and Discussion
### Main Sources of GHG Emissions, Including Sources in Milk Production
These data confirm that the emission source structure is strongly determined by local conditions, production intens  
Figure 8: Diagram of greenhouse gas emissions related to milk production on the farm (the authors’ own diagram prepared on the basis of research results in the publication [40]). The figure shows two boundaries of the dairy production system and their associated GHG and CF emissions: the left-hand side encompasses the system’s external boundaries (heading: emissions outside dairy farm), while the right-hand side encompasses the system’s internal boundaries (heading: emissions on dairy farm). This review focuses primarily on direct GHG and CF emissions (enteric fermentation; manure and soil management; on-farm/internal feed production and pasture management) within dairy farms, thus focusing on the internal boundaries of this system. Emissions from fertiliser management (especially manure storage and spreading) remain significant and strongly dependent on the technologies adopted [45; 46]. Manure management represents the second key source of emissions on farms. It includes CH\({}_{4}\) and N\({}_{2}\)O emissions generated during the storage and application of natural fertilisers. A study by [PERSON] et al. [22] showed that farms using slurry in uncovered tanks emit significantly more CH\({}_{4}\) and N\({}_{2}\)O than those that use roofed systems or process waste/by-products in biogas plants. An analysis by [PERSON] and [PERSON] [47] demonstrated that the implementation of anaerobic fermentation reduced emissions from manure by 0.26 kg CO\({}_{2}\) eq kg\({}^{-1}\) milk, which translated into a noticeable improvement in environmental performance. The third dominant emission source includes processes related to the production and supply of feed, especially feed purchased from external sources, and emissions associated with crop fertilisation. In India, the share of emissions related to feed production was 23% [4]. In systems based on a large proportion of purchased feed, indirect (upstream) emissions can account for as much as 30% of the CF [29]. A study by [PERSON] et al. [27] showed that the use of HSG can reduce nitrogen (N) emissions from urine and, consequently, N\({}_{2}\)O emissions from the soil (which is important in the context of reducing emissions from feeding systems). In Brazil, where intensive feed production is common, the emissions associated with the purchase and transportation of feed ingredients significantly increased the CF [23]. Although enteric fermentation remains the most important emission source in milk production, emissions from manure management and intermediate processes are becoming increasingly important, especially under more complex and intensive production systems [20; 21; 25]. The optimisation of these three main components, namely fermentation, fertiliser and feed, provides a key direction for an effective reduction in greenhouse gas emissions from the dairy sector [30; 38; 39]. Many LCA analyses emphasised the significance of indirect emissions, e.g., those related to the production of artificial fertilisers or imported feed components, especially on farms that rely on purchased feed. In tropical countries, land use and landscape transformation are significant sources of emissions. Indirect GHG emissions, often referred to as off-farm or secondary emissions, constitute a significant component of the total CF of milk production. These emissions originate from processes associated with the manufacture and transport of farm inputs such as synthetic fertilisers, concentrated feed, pesticides, energy, machinery, and replacement animals [9]. LCA studies emphasised that although direct emissions (e.g., enteric methane) dominate, indirect emissions can account for up to 25-30% of the total CF depending on the production system and input intensity [41]. For instance, [PERSON] et al.