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 18–35 kg 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.korsaethplanteforsk.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
0167-880900 – see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 8 8 0 9 0 0 0 0 1 2 9 - 8
200 A. Korsaeth, R. Eltun Agriculture, Ecosystems and Environment 79 2000 199–214
limiting nutrient for producing food and maintaining the level of soil N is essential for sustaining agricul-
tural productivity. Agronomic practices affect the balance between
production and mineralisation of soil organic N. The characteristically slow turnover of the N pools implies
that low input farming systems may sustain fairly high productivity at the cost of a gradual decline of
the soil organic N. The degree to which an agronomic system maintains the soil organic N level is thus one
of several measures of its sustainability. This crite- rion is conditional, however, since net changes also
depend on the history of the soil. It is difficult to avoid a net reduction of soil organic N in soils with a
high content of mineralisable organic N, especially in arable cropping systems Christensen, 1990; Uhlen,
1991; Heenan et al., 1995; Thomsen and Christensen, 1998. At the other extreme, most cultivation regimes
will result in a net accumulation of soil organic N on soils with very low initial soil organic N levels Fet-
tell and Gill, 1995; Poulton, 1995; Raun et al., 1998. Thus the sustainability of cultivation regimes with
respect to soil organic N levels can only be compared on equal terms, i.e., when the regimes are run side
by side on the same type of soil and under identical climatic conditions.
Changes in the soil N pool can only be observed over an extended time Poulton, 1995, since the an-
nual changes are small as compared to the total pool size e.g., Uhlen, 1991. Long term experiments are
therefore needed Dick, 1992. It is, however, desirable to obtain information on trends at an early stage, in or-
der to correct the development in the present cropping systems. Good correlations have been found between
calculated N balances and changes in soil N Uhlen, 1989; Nyborg et al., 1995, and thus nitrogen mass
balance N balance studies are a suitable approach to analyse agroecosystems Wood et al., 1991.
Systems with a similar difference between inputs and outputs of N may, however, differ greatly in their
losses of N to the environment, as high losses may be counteracted by high inputs. One major path for
N losses from agriculture is the transport via surface and drainage runoff, and the resulting pollution of wa-
ter resources has become an increasingly important problem Kristensen et al., 1995. In an ideal crop-
ping system, should not only the reduction of soil N be minimised but also the N runoff. Reliable measure-
ments of N runoff are difficult to obtain and require rather expensive lysimeter trials e.g., Bergström and
Brink, 1986; Uhlen, 1994; Thomsen and Christensen, 1998. Finding a simple but robust way to estimate
N runoff would thus be a great advantage when eval- uating cropping systems. Different factors have been
found to correlate with N runoff, such as fertiliser level Bergström and Brink, 1986; Bergström, 1987, pre-
cipitation Jenkinson, 1990, soil mineral-N content in early autumn Bergström and Brink, 1986; Vagstad
et al., 1997 and crop yield Vagstad et al., 1997. Hal- berg et al. 1995 stated in more general terms, that
the N balance fertiliser N plus N applied with ma- nure minus harvested N is an expression of the to-
tal potential for N losses from an agroecosystem, and thus an indirect indicator of N runoff. The direct rela-
tionship between N balances and N runoff at the field level has, however, seldom been investigated.
The Apelsvoll Cropping System Experiment was established in 1988–1989 with the aim of developing
sustainable and environmentally sound cropping sys- tems Eltun, 1994. The experiment consists of six dif-
ferent cropping systems with rotations of either mainly arable or mainly forage crops, ranging from low to
high inputs of N and other production factors. On the basis of results from the first 8 years of this experi-
ment one entire crop rotation, the objective of the study presented here was, i to quantify the major N
flows in the cropping systems, using a mass-balance approach, in order to analyse possible changes in the
soil N content, and ii to test the usefulness of mass balance calculations for predicting N runoff.
2. Materials and methods
