Nitrogen balances at the crop and farm-gate scale in livestock farms in Italy

Nutrient balances are often used to represent nutrient flows and to produce sustainability indicators. A soil surface nutrient budget (at the crop scale) and a farm-gate budget (at the farm scale) were calculated over 41 commercial Italian livestock farms. The objectives were to estimate the N use efficiency of the main farm types using the two balances independently, and to assess and discuss the relationship between the two different budget methods. The N surpluses calculated as a farm-gate balance (FGBS) or at the soil surface scale (CBS) ranked livestock farms in a similar manner. The suckling cow farms (SC) showed the best sustainability, BB (beef breeding) and DC (dairy cow) farms were intermediate, while PB (pig breeding) farms were the worst due to their weaker link between breeding activities and farm crops. The CBS was mainly influenced by the manure input, while the FGBS was mainly influenced by the purchased animal feeding in the PB, BB and DC farms, and by the mineral fertiliser in the SC farms. Other information can be derived from a combination of the N flow quantified in the farm-gate balance and the crop balance; two examples are given concerning an estimation of gaseous losses and of animal N excreta for the different animal categories. It has been concluded that even though N balances cannot be directly used to estimate the actual environmental impact of different farming systems, they remain reliable indicators to help discriminate between different farm types. (C) 2007 Published by Elsevier B.V.