Resource-efficient use of land and animals-Environmental impacts of food systems based on organic cropping and avoided food-feed competition

摘要

Current food systems are resource-inefficient, as farm animals consume large quantities of human-edible crops and large amounts of external fossil fuel-based inputs are used for energy and fertilisers. In this study, we assessed the production capacity and environmental performance of an alternative theoretical regional food system based on organic production, avoided food-feed competition and agriculture that is self-sufficient in bioenergy. Livestock in the system are reared solely on feeds that do not compete with food production, i.e. grass from permanent pastures, temporary grass-clover leys and food industry by-products. We modelled the effect of this food system on food production, land use, environmental impacts and nutrient flows, using the Nordic region as a case. As crop rotations under organic farming need leguminous forage crops to supply nitrogen and control weeds, substantial amounts of grass biomass suitable for feeding ruminants are produced in the system. Modelling showed that such a food system could feed 109% of the projected Nordic population in 2030 in a scenario where ruminant production is limited by the availability of semi-natural grasslands, and 130% in a scenario in which all grass biomass produced in organic crop rotations is used as animal feed. However, even when all grass biomass is used for animal feed, the associated reduction in meat production led to diets with 81% less meat compared to current consumption in the Nordic region. Using all ley from the organic crop rotations as livestock feed would result in greater total food output and reduced land use per person, but also a larger climate impact per person due to more livestock production. There is thus a trade-off between optimising the food system for efficient land use or for 'climate efficiency'. Assessments of nutrient supply showed nitrogen and phosphorus deficits in both scenarios, but particularly in the scenario in which all grass biomass is used for animal feed, due to nutrient losses in animal production. Increased recycling from society and other innovative sources of essential soil nutrients are needed to counterbalance removal and losses. Through utilising leftover streams and hence minimising food-feed competition and reducing livestock production, we show that organic agriculture can maintain high food output, sufficient to feed the future Nordic population and more, despite lower yields.