Abstract of PhD Thesis

Greenhouse gas emissions from Irish livestock production systems

John Casey, University College Dublin (2005)

Actions to moderate the major emission contributors of enteric fermentation, fertiliser and manure management on farms should not simply move the emissions elsewhere in the system, but actually reduce them. Life cycle assessment methodology was used to provide an objective framework for estimating emissions and to evaluate emission management scenarios with respect to kg CO2 eq. emitted per unit of energy corrected milk (ECM) (dairy system) and live weight (suckler beef and sheep systems) produced to the farm gate. European Union agri-environmental schemes aim to reduce the environmental impact of agricultural production, but the schemes were developed before consideration of greenhouse gas emissions (GHG) from agriculture. Nevertheless these schemes were assessed for dairy and beef systems to ascertain whether reductions in GHG emissions could be attained. An average dairy unit was defined from national census data and emissions were compartmentalised to calculate a total emission of 1.50 kg CO2 eq kg-1 (energy corrected milk) yr-1. Of the total emissions, 49% was enteric fermentation, 21% fertiliser, 13% concentrate feed, 11% dung management and 5% electricity and diesel consumption. Scenario testing indicated that more efficient cows with extensive management could reduce emissions by 14-18%, elimination of non-milking animals could reduce emissions by 14-26% and a combination of both could reduce emissions by 28-33%. It was concluded that the evolution of the Irish dairy sector, driven by the Common Agricultural Policy (CAP) should result in reduced GHG emissions. To evaluate these results a case study involving ten functioning farms (five functioning conventionally and five within an agri-environmental scheme) was carried out. The agri-environmental scheme farms operate extensive systems from 40 to 120 milking cows producing between 3032 to 5946 kg (ECM) per cow per lactation. The cows are fed on grazed grass, conserved silage and concentrates. Supplementation ranged between 250 to 620 kg cow-1 yr-1. The conventional (more intensive) farms had between 30 and 77 milking cows producing 4736 to 6944 kg (ECM) per cow per lactation. Supplementation ranged from 400 to 1000 kg cow-1 yr-1. The emissions from each dairy unit were estimated using published emissions factors and possible error was evaluated by using ranges of values for each factor. Emissions were calculated to range from 0.92 to 1.51 kg ECM-1 yr-1 and 5924 to 8323 kg CO2 equivalent ha-1. On average, total emissions from conventional farms were around 18% (p = 0.01) greater than the agri-environmental scheme farms and emissions per hectare (total area required) were 17% greater (p = 0.02) but there was no significant difference (p = 0.335) in terms of emission per unit of energy corrected milk produced.

The typical suckler-beef system was estimated to produce 11.92 kg CO2 LW yr-1. Scenarios were developed that examined using both beef-bred animals (Charolais, Simmental and Limousin) and dairy-bred animals (Holstein-Fresian). By scaling total GHG emissions relative to a FU of live weight per year (kg CO2 kg LW yr-1), it was possible to estimate both the emissions and the potential for emissions reduction by adopting alternative management. The system evaluated was derived from national census data. For beef-bred animals the cow contributed a large amount to the total emissions whereas for dairy-bred beef production the allocation from the cow was much less. In terms of diet supplementation for GHG emissions reduction, a broad range of diet combinations were evaluated and showed no major reduction potential compared to, or within, the grass-dominated system. The problems of overproduction within the European Union countries and the environmental impact of agriculture have lead to the introduction of schemes, which aim to reduce both. Beef production forms a large component of the Irish agriculture industry and accounts for over one quarter of agricultural economic output. Recently, the European Common Agricultural Policy (CAP) has been re-evaluated to include supplementary measures, which encompass the environmental role of agriculture rather than just the production role. A life cycle assessment (LCA) type method was adopted to estimate emissions per kg of CO2 equivalent per kg live-weight (LW) leaving the farm-gate per annum (kg (CO2) kg-1 (LW) yr-1) and per hectare (kg (CO2) kg (ha-1) yr-1). Fifteen units engaged in suckler-beef production (five conventional, five in an Irish agri-environmental scheme, and five organic units) were evaluated for emissions per unit product and area. The average emissions from the conventional units were 13.0 kg (CO2) kg-1 (LW) yr-1, from the agri-environmental scheme units 12.2 kg (CO2) kg-1 (LW) yr-1, and from the organic units surveyed 11.1 kg (CO2) kg (LW) yr-1 per unit product. The average emissions per unit area from the conventional units were 5346 kg (CO2) ha-1 yr-1 kg (CO2) kg (ha) yr-1 from the agri-environmental scheme units 4372 kg (CO2) ha-1 yr-1 kg (CO2) kg  yr-1, and from the organic units surveyed 2302 kg (CO2) ha-1 yr-1 kg (CO2) kg (ha) yr-1. Results indicated that moving towards extensive production could reduce emissions per unit product and area but live weight production per hectare would be reduced.

The overall emissions from the mid-season lamb production system evaluated were 11.25 kg CO2 equivalent per kg LW and 4247 kg CO2 equivalent per HA. Scenario testing indicated that moving towards more extensive production would reduce emissions per kg LW and intensifying the system would increase emissions. The major problem with adopting more extensive production would be a probable loss of productivity.

Overall holistic analysis is advantageous for quantifying emissions from livestock production because it facilitates greater understanding of the system and in particular the effect of implementing GHG emission reduction options. The holistic approach is important to ensure emissions are genuinely reduced rather than transferred elsewhere.