Under Nordic conditions, adequate organic cereal yields may be
achieved in rotation with forage crops, but poorer yield levels have
been found in organic systems without animal manure (Bakken
et al., 2006; Korsæth and Eltun, in press; Olesen et al., 2007). On an
area basis, about one third of the organic grain in Norway is
produced within stockless systems and this proportion is expected
to increase. Under such management, crops rely largely for their
nutrient supply on the mineralization of green manure (including
legumes), crop residues and soil organic matter (SOM). Favourable
soil structure is considered important both for mineralization and
to permit sufficient root growth for optimum nutrient uptake
(Christensen, 2001; Pietola, 2005).
The avoidance of compaction is essential for the maintenance of
good soil structure (Ha˚ kansson, 2005). Besides the timing of traffic
in relation to soil moisture, compaction risk is associated with the
weight of machinery used, especially that of tractors