A modelling study of nitrogen deposited to arable land from the atmosphere and its contribution to nitrate leaching

Atmospheric nitrogen (N) makes a significant contribution to the N inputs to agricultural systems and is a major eutrophying and acidifying input to natural and semi-natural ecosystems. We have estimated the nitrogen deposited to arable land at Rothamsted and at two Nitrate Vulnerable Zones (NVZs) in the UK, Lichfield and the River Wavenecy. Using the SUNDIAL N cycle model calibrated against measured soil mineral N and leaching losses at Rothamsted, we have calculated the contribution of deposited N to nitrate leaching under a range of crops growing on the major soil series in the NVZs. Approximately 44, 46 and 28 kg N/ha per yr are deposited to arable land around Rothamsted and in the Lichfield and Waveney NVZs, respectively Most of this is dry-deposited in oxidized forms; nitrogen dioxide and nitric acid are the main components, arising mostly from industry, home heating and vehicle emissions. SUNDIAL predicts that current total leaching losses from arable crops average 39 kg W/ha per yr in the Lichfield NVZ and 22 kg/ha per yr in the Waveney NVZ. Atmospheric N contributes about 28% of the N leached from arable land in the Lichfield NVZ and 17% in the Waveney NVZ, a very significant amount. There is little variation in total leaching or the atmospheric contribution to it between soil series within each NVZ, but much variation with crop type and the weather: atmospheric N can comprise over 40% of the N leached under spring cereals in some years.