Forage systems and sustainability of milk production: feed efficiency, environmental impacts and soil carbon stocks

Abstract Farm sustainable intensification is an important strategy to reduce environmental impacts, which can be obtained in particular through improvements in the milk production per cow and feed efficiency, as well as by increasing the net primary production of the Utilized Agricultural Area. Farming systems that are mainly based on multi-annual/perennial forages may increase soil carbon (C) sequestration, which is a significant greenhouse gases mitigation strategy. The aim of the present study has been to identify the forage systems related to dairy farms that are able to maximize feed production and to improve feed efficiency and C sequestration, in order to achieve the best environmental sustainability result. A group of 46 dairy farms was selected to represent the most widespread forage systems in Northern Italy. The identified forage systems were: CONV, conventional corn silage system; MIXED, low intensity mixed system; HQFS, high quality forage system; WICE, winter cereal silage system; PR DRY, hay system for Parmigiano Reggiano PDO cheese production and PR-FRESH, hay and fresh forage system for Parmigiano Reggiano PDO cheese production. Primary data were collected to carry out a life cycle assessment. Soil samples of representative crops of the forage systems were collected to determine in particular the soil organic carbon density and soil organic matter. The WICE, CONV and HQFS forage systems provided the greatest amount of dry matter (DM) per hectare, whereas the PR FRESH system showed the highest soil C density. The LCA results showed that the HQFS system registered the lowest values for all the impact categories (except for land occupation and the use of non-renewable resources), probably due to the higher milk production, both in terms of individual production (fat and protein corrected milk/head) and feed efficiency (kg milk/kg DMI). More intensive systems, such as HQFS, demonstrated that the milk production per cow and feed efficiency are negatively related to the impact per kilogram of product. The HQFS system also resulted to be more sustainable, in terms of feed self-sufficiency, as a high amount of DM per hectare. However, as far as this forage system is concerned, there is still room to strengthen environmental sustainability, since HQFS also showed the lowest C soil density. Further investigations are needed to consider environmental sustainability over a wider spectrum.