Life cycle assessment of drought-tolerant grasses for sustainable dairy farming

Dairy farming in Flanders faces increasing challenges from climate change, particularly the prevalence of droughts. Traditional forages such as perennial ryegrass are highly susceptible to drought, resulting in significant yield losses and increased environmental impacts. This study applies a Life Cycle Assessment to evaluate the environmental implications of adopting drought-tolerant grasses, such as tall fescue, and integrating red clover into dairy cow diets. The analysis used a model farm with 100 dairy cows and 75 youngstock, and applied eight scenarios that varied by forage type, the inclusion of red clover, and weather conditions across wet (2021 and 2023) and dry years (2022). The cradle-to-farm-gate system boundary included feed production, manure management, and enteric methane emissions. Resulting emissions were expressed per kilogram of fat and protein corrected milk and per cow per day. Replacing perennial ryegrass with tall fescue increased forage yields, particularly during dry conditions, with tall fescue producing between 2 and 4 tons more per hectare than perennial ryegrass. This led to reduced land use and lower environmental impacts from feed production per hectare. However, tall fescue diets exhibited reduced digestibility, which contributed to increased enteric methane emissions and emissions from manure, both resulting in a higher climate impact per kilogram of milk. For example, during the dry year, the climate impact for tall fescue based diets was 1.09 kilograms of CO2 eq per kilogram of milk, compared to 1.06 for perennial ryegrass based diets. Furthermore, reliance on soy increased within fescue diets, contributing significantly to the environmental footprint of feed purchases, which accounted for up to 40% of the total climate impact in some scenarios. The inclusion of red clover up to 3.55 kg dry matter per day or 14,9 % of the total ration, enhanced sustainability in both perennial ryegrass and tall fescue systems. Red clover required less fertilizer and diesel inputs, reducing emissions associated with feed production. Its inclusion decreased the reliance on soy and improved digestibility in tall fescue diets by 1.3% , partially offsetting their negative impacts on enteric methane emissions and emissions from manure storage, with a reduction up to 3.8% per unit of milk. In perennial ryegrass-based diets, red clover also lowered overall environmental impacts, with reductions of up to 1.3% in the climate impact per kilogram of milk compared to diets without. Drought conditions increased the environmental impacts of all forage systems. Perennial ryegrass yields dropped from 15.5 tons per hectare to 10.0 in 2022 , necessitating additional maize purchases, while tall fescue yields declined only from 17.5 to 14.0. Tall fescue demonstrated greater resilience, resulting in smaller increases in climate impact during drought compared to perennial ryegrass. This underscores its potential to improve the robustness of forage systems under climate stress. This study highlights the trade-offs between higher yields and lower nutritional value when transitioning to tall fescue, and the complementary benefits of red clover from a LCA perspective. Limitations include reliance on a model farm and the inability to fully isolate dietary effects. Future research should expand to diverse farming systems and explore the long-term impacts of these dietary changes to provide a holistic understanding of the environmental performance of drought-tolerant forages.