Water footprinting of dairy farming in Ireland

In the context of global water scarcity, water footprints have become an important sustainability indicator for food production systems. To improve the water footprint of the dairy sector, insight into freshwater consumption of individual farms is required. The objective of this study was to determine the primary contributors to freshwater consumption (i.e. water use that does not return to the same watershed) at farm-gate level, expressed as a water footprint, for the production of one kg of fat-and-protein corrected milk (FPCM), on 24 Irish dairy farms. This is the first study that uses detailed farm level data to assess the water footprint of a large set of Irish dairy farms. The water footprint comprises of the consumption of soil moisture due to evapotranspiration (green water), and the consumption of ground and surface water (blue water), and includes freshwater used for cultivation of crops for concentrate production, on-farm cultivation of grass or fodder and water required for animal husbandry and farm maintenance. The related impact of freshwater consumption on global water stress from producing milk in Ireland was also computed. Over the 24 farms evaluated, the production of milk consumed on average 690 L water/kg FPCM, ranging from 534 L/kg FPCM to 1107 L/kg FPCM. Water required for pasture production contributed 85% to the water footprint, 10% for imported forage production (grass in the form of hay and silage), concentrates production 4% and on-farm water use ∼1%. The average stress weighted water footprint was 0.4 L/kg FPCM across the farms, implying that each litre of milk produced potentially contributed to fresh water scarcity equivalent to the consumption of 0.4 L of freshwater by an average world citizen. The variation of volumetric water footprints amongst farms was mainly related to the level of feed grown on-farm and levels of forages and concentrates imported onto the farm. Using farm specific data from a subset of Irish dairy farms allowed this variability in WF to be captured, and contributes to the identification of improvement options. The biggest contribution to the water footprint of milk was from grass grown with green water, which is a plentiful resource in Ireland. This study also indicates an opportunity for present and future milk production systems to source feed ingredients from non-water stressed areas to further reduce the burden on freshwater resources, especially in countries that utilise confinement systems that have a higher proportion of concentrate feed in the dairy cow's diet.