Agriculture, Ecosystems and Environment 79 (2000) 199–214 Nitrogen mass balances in conventional, integrated and ecological cropping systems and the relationship between balance calculations and nitrogen runoff in an 8-year field experiment in Norway Audun Korsaeth ∗ , Ragnar Eltun Apelsvoll Research Centre, The Norwegian Crop Research Institute, N-2849 Kapp, Norway Received 9 March 1999; received in revised form 8 December 1999; accepted 14 December 1999 Abstract For a cropping system to be sustainable, should not only the soil nitrogen (N) content be preserved but also the N runoff be minimised. Finding a simple but robust way to estimate N runoff would thus be a great advantage when evaluating cropping systems. In this study all major N flows in six different cropping systems, each covering 0.18 ha of a separately pipe drained field lysimeter, located in southeast Norway, were either measured or estimated over a period of 8-years. The effect of the cropping system on the soil N content was evaluated using mass balances of total N, and the usefulness of such N balances to predict N runoff (total N losses via drainage and surface water) was investigated. The experiment included systems with conventional arable cropping (CON-A), integrated arable-cropping (INT-A), ecological arable cropping (ECO-A), conventional forage cropping (CON-F), integrated forage cropping (INT-F), and ecological forage cropping (ECO-F). All the arable cropping systems resulted in a net reduction in the calculated soil N pool, and the reduction increased with decreasing N input. The only system, which did not alter the soil N content, was CON-F. The largest net reduction was estimated for ECO-A and ECO-F, which averaged 45 and 43 kg N ha −1 per year, respectively. The N runoff from the systems was in the range of 18–35kg N ha −1 per year, with highest losses from the two conventional and lowest from the two ecological systems and INT-F. The forage systems had lower N runoff than the arable systems. The INT-F system appeared to be the most favourable system in terms of both soil N balance and N runoff. When the annual (May–April) N balance, calculated as N fertiliser +N slurry −N harvest , the annual precipitation and the precip- itation from the previous year were used as predictors in a linear regression model, 87 and 65% of the variation in N runoff could be explained from the arable and forage cropping systems, respectively. The average N balance calculated for all years, on its own predicted 86% of the variation in N runoff from the arable systems. Mass N balances were thus found to be a useful tool for predicting N runoff, especially in systems with mainly arable crops. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Cropping systems; Leaching; Nitrogen balances; Nitrogen runoff; Predictor; Symbiotic N fixation; Sustainability; Total nitrogen ∗ Corresponding author. Tel.:+47-61-16-69-10; fax: +47-61-16-69-01. E-mail address: audun.korsaeth@planteforsk.no (A. Korsaeth) 1. Introduction There is increasing concern about the long term productivity of soils as a resource base for food production (Dick, 1992). Nitrogen (N) is the major 0167-8809/00/$ – see front matter ©2000 Elsevier Science B.V. All rights reserved. PII:S0167-8809(00)00129-8