N transfer in three-species grass-clover mixtures with chicory,ribwort plantain or caraway

Background and aims

There is substantial evidence that legume-derived Nitrogen (N) is transferred to neighboring non-legumes in grassland mixtures. However, there is sparse information about how deep rooted non-legume forage herbs (forbs) influence N transfer in multi-species grasslands.

Methodology

Red clover (Trifolium pretense L.) was grown together with perennial ryegrass (Lolium perenne L.) and one of three forb species: chicory (Cichorium intybus L.), ribwort plantain (Plantago lanceolata L.) or caraway (Carum carvi L.) in a field experiment. During the first year after the establishment, red clover leaves were labeled with ¹⁵N-urea to determine the N transfer from red clover to companion ryegrass and forbs.

Results

On an annual basis, up to 15 % of red clover N was transferred to the companion ryegrass and forbs, but predominantly to the grass. The forb species did not differ in their ability to take up clover N, but biomass production and soil N acquisition was higher in chicory and plantain than in caraway.

Conclusions

Grass relied to a great extent on clover N, whereas forbs relied on soil N. Soil ¹⁵N-enrichment indicated that N transfer occurred in the upper soil layers and that a dependence on clover-derived N did not necessarily give grass a growth advantage.