Forage legume species determine the nutritional quality of binary mixtures with perennial ryegrass in the first production year

There is increasing interest in forage legumes as ruminant feeds in Europe as alternatives to using mineral N fertilizer on temporary grassland. Successful management of grass–legume mixtures depends on the suitability of the forage legume species to the cutting frequency, and its nutritional quality for animals. An experiment was completed in 2004 and 2005 on two sites at the University of Kiel (Germany) to examine the response of legume-perennial ryegrass (Lolium perenne L.) mixtures to cutting frequency in terms of dry matter (DM) yield, N₂ fixation, net energy for lactation (NEl), plant cell wall content, and crude protein (CP) content and CP fractions in the first production year. Different legumes in binary mixtures with perennial ryegrass (L. perenne L.), red clover (Trifolium pratense L.), white clover (Trifolium repens L.), hay-type and grazing-type alfalfa (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), Caucasian clover (Trifolium ambiguum M. Bieb.) and two monocultures of perennial ryegrass (with and without cattle slurry supplying 20gN/m²) were examined under two cutting frequencies. All legume–grass mixtures outperformed perennial ryegrass with and without slurry in terms of DM yield, irrespective of cutting frequency. Production from both birdsfoot trefoil and Caucasian clover in grass–legume mixtures were very low, similar to unfertilized pure stands of grass, and the low production was consistent with slow and deficient establishment of birdsfoot trefoil and Caucasian clover, as observed by others. Nutritional quality of Caucasian clover was comparable to white clover. The companion grass benefited from the N transferred by forage legumes and their growth habit. This was especially evident for white clover, resulting in the highest companion grass yield and, in consequence, high mixture DM yield in both the 3 and 5 cut systems. Differences in agronomic performance of the legume–grass mixtures, and the grass monocultures, were related to the legume species in the mixture rather than cutting system. Forage legume species determined the nutritional quality and yield of binary mixtures with perennial ryegrass in the first production year.