Consequences of including adapted white clover in northern European grassland:: transfer and deposition of nitrogen

The interspecific transfer of nitrogen (N) between white clover (Trifolium repens) and smooth meadow grass (Poa pratensis) in legume-based grasslands was assessed under North European field conditions using N-15 individual plant leaf labelling. On average 50% of N in the grass was transferred from the white clover and about 6% of N in white clover was transferred from the grass. This corresponds to 2.5 and 0.3 g N m(-2) being transferred over the growing season between the two species, respectively, and demonstrates that a significant part of the total N of the grass is coming through interspecific transfer. The majority of the N-15 transferred was within a period of 20 days at relatively low soil temperatures. This implies that there is a need for a new focus on direct transfer pathways or exudation and transfer of organic N sources. Rhizodeposition in the top 10 cm of the soil was found to be 2.98 g N m(-2) on average over the growing season for the grass and white clover mixture. Inclusion of adapted white clover varieties in the low-input grassland systems of northern Europe will lead to a substantial contribution of N.