NPK farm-gate nutrient balances in dairy farms from Northwest Portugal

Abstract

Farm-gate nutrient balances (N, P and K) were analysed in three groups of dairy farms from NW Portugal – medium, intensive and very intensive farms – during 3 consecutive years, 2003, 2004 and 2005. Results showed that the N surplus per hectare with values between 200 and 850 kg N ha −1 was positively correlated with the milk production per ha and the stocking rate of the farm, whereas the P and K surpluses showed fewer variations between groups. In all farms the main inputs were the mineral fertilizers and the feed concentrates whereas milk was the main output. Farmers involved in the study were advised in terms of nutrient management and significant decreases in the nutrient surpluses were observed during the 3 years study, mainly due to a decrease of the inputs, namely fertilizers. We conclude that advisory campaigns among farmers are efficient to reduce the nutrient surpluses. The N losses via NH 3 emissions at farm scale were also estimated accordingly to IPCC emission factors and it appeared that such losses were significant and had to be considered together with the nutrient surpluses when strategies to enhance nutrient management are defined. On average, higher N surplus per hectare were observed in the studied dairy farms from NW Portugal relatively to other European regions, but NW Portugal present lower N surplus per production unit (kg milk) as well as higher N efficiency. Nevertheless, a target limit of 450 kg N ha −1 for N surplus should be easily reached as a first step by most of the farms of NW Portugal by improving nutrient management at farm scale. However, more efforts will be necessary to reduce NPK surplus and NH 3 emissions to the mean values in a per hectare basis found in other European dairy regions with less intensive systems.