Nutrient flows in lowland dairy farms in the Italian Alps

A traditional dairy production system is still common today in the mountain environment of the Italian Alps, enhancing the economic valorisation of milk through the production of quality cheese such as Fontina PDO (Protected Designation of Origin), and favouring the agroenvironmental management of marginal areas. This type of dairy system depends mainly on summer grazing: farmers set up the farm stock on the basis of the high-altitude grassland areas available. For the rest of the year, the livestock is housed on the farm lowland, consequently reaching high stocking rates. Since grassland areas are limited in size here, animal feeding is largely based on acquired forages. In order to study the environmental sustainability of the lowland farm areas, agronomic management, nitrogen (N) and phosphorus (P) farm-gate balances were calculated for 22 livestock farms in the Valle d’Aosta region. Lowland surfaces show a quite high variability, with an average value of 6.8 ha. An unbalanced stocking rate referred to the lowland is common showing an average value of 5.7 livestock units (LU) ha–1, but reaching a maximum of 26.8 LU ha–1. Lowland milk production is approximately 1700 kg per LU per year, but some farms could reach 3500 kg per LU The feed efficiency varies from 1.1 to 4.7 kg milk per kg feed, depending on the farm feeding strategy. The average N farm-gate balance is equal to 75 kg N ha–1. The two main input components are represented by purchased hay and feed, both showing the highest variability between farms. The output data also differ substantially among farms. The manure sold is the most important output component and represents 70% of the total output on average. The P farm gate balance surplus is equal to 6 kg ha–1, but more than 25% of the farms considered show a negative value. The surpluses calculated in this work can be compared with the values belonging to a distribution calculated for bovine farms under different management and environmental conditions in Italy and Europe. They occupy the lower part of the distribution and are similar to those measured in mountains or other extensive environments.