Nitrous oxide emission from dairy farming systems in the Netherlands

A large part of the nitrogen (N) input in dairy farming systems in the Netherlands is lost from the system via N leaching and volatilization of gaseous N compounds, including the greenhouse gas nitrous oxide (N(2)O). The aim of the present study was to quantify N(2)O emission from dairy farming systems in the Netherlands, using a whole-farm approach. A total of 14 N(2)O sources was identified and emission factors were derived for each of these using literature. Figures are presented for the amounts of N(2)O produced per kg herbage N produced (ranging from 4 to 89 g N(2)O-N kg(-1) herbage N), depending on soil type and grassland management. Using Monte Carlo simulations, variations in mean total N(2)O emissions from the different sources were calculated for three model dairy farming systems differing in nutrient management. These different farming systems were chosen to assess the effect of improved nutrient management on total N(2)O emission. The total direct N(2)O emissions ranged from 15.4 +/- 9.4 kg N(2)O-N ha(-1) yr(-1) for the average dairy farming system in the eighties to 5.3 +/- 2.6 kg N(2)O-N ha(-1) yr(-1) for a prototype of an economically feasible fanning system with acceptable nutrient emissions. Leaching-derived, grazing-derived and fertilizer-derived N(2)O emissions were the major N(2)O sources on dairy farming systems. The total direct N(2)O emissions accounted for 3.2 to 4.6% of the N surplus on the dairy farming systems, suggesting that only a small amount of N was lost as N(2)O. Total N(2)O emissions from dairy farming systems in the Netherlands were estimated at 13.7 +/- 5.1 Gg N yr(-1), which is about 35% of the estimated total N(2)O emission in the Netherlands. II is concluded that improvement of nutrient management of dairy farming systems will significantly decrease the N(2)O emissions from these systems, and thus the total N(2)O emission in the Netherlands.