Forage management to improve on-farm feed production, nitrogen fluxes and greenhouse gas emissions from dairy systems in a wet temperate region

Improving forage cropping systems and grasslands are key factors to enhance on-farm resources and sustainability in wet temperate regions of North Spain, contributing to the preservation of associated ecosystem services. This study evaluates the potential of agronomic field management for mitigating greenhouse gas emissions (GHG) and enhancing nitrogen (N) fluxes that can support an increase in on-farm forage resources, thus reducing the dependency on external inputs (fertilizers and feed products). A survey conducted in a weighted sample of 40 dairy farms in Cantabria showed four characteristic forage systems according to field management based on grazing, zero-grazing, conserved forages and growth of maize. The semi-dynamic whole farm model FarmAC was used to characterize a model farm representing an average farm in each of the forage systems including field area and use, number of cows and heifers, diet, milk yield and slurry management. The model was applied to simulate carbon (C) and N fluxes at the farm level, and to calculate feed balances, GHG emissions and the N surplus. Farms were simulated under current forage management (baseline) and under scenarios of enhanced forage production. Milk yield, the balance between forage production and consumption in the animal diet, and between manure generation and application in the field, were used as reference for accepting model simulations. The results from the scenarios indicate that increasing forage productivity, not only reduces the external dependence for feeding animals, but also would have a clear potential for mitigating yield-scaled farm GHG emissions. However, this potential appears to have a limit when N surplus exceeds a threshold value. Rotational grass-clover would have additional benefits in terms of reduced N fertilizer costs and soil carbon enhancement.