How much grassland biomass is available in Ireland in excess of livestock requirements?

Abstract

Grassland is a dominant biomass resource in Ireland and underpins most animal production systems. However, other commercial uses for grassland biomass exist, including, for example, the production of biogas through anaerobic digestion for the generation of heat, electricity and transport fuel. The objective of this study was to estimate the annual grassland resource available in Ireland in excess of livestock requirements under six contrasting scenarios. Under current grassland management and production practices there is an estimated average annual grassland resource of ca. 1.7 million tonnes of dry matter (DM) available in excess of livestock requirements. Only a small proportion of this resource (0.39 million tonnes of DM per annum) would be available if the targets set out in ‘Food Harvest 2020’ were achieved. However, increasing nitrogen (N) fertiliser input (to the limit permitted by the E.U. Nitrates Directive) combined with increasing the grazed grass utilisation rate of cattle (from 0.60 to 0.80 kg DM ingested by livestock per kg DM grown) has the potential to significantly increase this average resource to 12.2 million t DM/annum, even when allowing for achievement of ‘Food Harvest 2020’ targets. Under these scenarios, alternative uses for grassland biomass such as anaerobic digestion and green biorefining would not compete with traditional dairy, beef and lamb production systems, but could provide an alternative enterprise and income to farmers.