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 2O). The aim of the present study was to quantify N2O emission from da iry farming systems in the Netherlands, using a whole-farm approach. A total of 14 N2O sources was identified and emission factors were deri ved for each of these using literature. Figures are presented for the amounts of N2O produced per kg herbage N produced (ranging from 4 to 8 9 g N2O-N kg(-1) herbage N), depending on soil type and grassland mana gement. Using Monte Carlo simulations, variations in mean total N2O em issions from the different sources were calculated for three model dai ry farming systems differing in nutrient management. These different f arming systems were chosen to assess the effect of improved nutrient m anagement on total N2O emission. The total direct N2O emissions ranged from 15.4 +/- 9.4 kg N2O-N ha(-1) yr(-1) for the average dairy farmin g system in the eighties to 5.3 +/- 2.6 kg N2O-N ha(-1) yr(-1) for a p rototype of an economically feasible fanning system with acceptable nu trient emissions. Leaching-derived, grazing-derived and fertilizer-der ived N2O emissions were the major N2O sources on dairy farming systems . The total direct N2O emissions accounted for 3.2 to 4.6% of the N su rplus on the dairy farming systems, suggesting that only a small amoun t of N was lost as N2O. Total N2O 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 N2O emission in the Netherlands. I I is concluded that improvement of nutrient management of dairy farmin g systems will significantly decrease the N2O emissions from these sys tems, and thus the total N2O emission in the Netherlands.