The simulated environmental impact of incorporating white clover into pasture-based dairy production systems

摘要

White clover (WC) offers an alternative source ofnitrogen (N) for pasture-based systems. Substitutingenergy- and carbon-intensive synthetic N fertilizerswith N derived from biological fixation by WC has beenhighlighted as a promising environmental mitigationstrategy through the omission of emissions, pollutants,and energy usage during the production and applicationof synthetic fertilizer. Therefore, the objectivewas to investigate the effect of the inclusion of WC inperennial ryegrass (PRG) swards on the environmentalimpact of pasture-based dairy systems. Cradle-to-farmgate life cycle assessment of 3 pasture-based dairy systemswere conducted: (1) a PRG–WC sward receiving150 kg of N/ha per year (CL150), (2) a PRG–WC swardreceiving 250 kg of N/ha per year (CL250), and (3)a PRG-only sward receiving 250 kg of N/ha per year(GR250). A dairy environmental model was updatedwith country-specific N excretion equations and recentlydeveloped N_2O, NH_3, and NO_3~− emission factors. Theenvironmental impact categories assessed were globalwarming potential, nonrenewable energy, acidificationpotential, and eutrophication potential (marine andfreshwater). Impact categories were expressed using 2functional units: per hectare and per metric tonne offat- and protein-corrected milk. The GR250 system hadthe lowest milk production and highest global warmingpotential, nonrenewable energy, and acidificationpotential per tonne of fat- and protein-corrected milkfor all systems. The CL250 system produced the mostmilk and had the highest environmental impact acrossall categories when expressed on an area basis. It alsohad the highest marine eutrophication potential forboth functional units. The impact category freshwatereutrophication potential did not differ across the 3 systems.The CL150 system had the lowest environmentalimpact across all categories and functional units.This life cycle assessment study demonstrates that thesubstitution of synthetic N fertilizer with atmosphericN fixed by WC has potential to reduce the environmentalimpact of intensive pasture-based dairy systemsin temperate regions, not only through improvementin animal performance but also through the reductionin total emissions and pollutants contributing to theenvironmental indicators assessed.