Opportunities and limitations in use of clovers as N-source in organic farming systems in Norway

From an economic as well as ecological point of view, transfer of clover N to the subsequent growing season should be maximised and the risk of environmental pollution minimised. It is very important in organic farming. Detailed studies on white clover lifespan indicated that the foliage is a main source of readily plant-available N as the leaves are short lived. However, the leaf N is largely lost from the plant foliage during the cold season. The risk of loss may probably be reduced by using winter-hardy cultivars that tend to reallocate resources to stolons and roots which are more persistent than leaves.