Contribution of subterranean clover (Trifolium subterraneum) to changes in morphological and physiological parameters raised alone and with birdsfoot trefoil (Lotus corniculatus)

Changes in some morphological and physiological parameters (leaves/stems ratio, total plastid pigments content, fixed amount nitrogen) of birdsfoot trefoil (Lotus corniculatus L.) (cv. Targovishte 1) and three subterranean clover subspecies, i.e. Trifolium subterraneum ssp. brachycalicinum (cv. Antas), Trifolium subterraneum ssp. yaninicum (cv. Trikkala) and Trifolium subterraneum ssp. subterraneum (cv. Denmark) were studied in a field trial in the Institute of Forage Crops, Pleven, Bulgaria (2012-15). Crops were grown alone (100%) and in mixtures as follows: birdsfoot trefoil + Trifolium subterraneum ssp. brachycalicinum (50:50%); birdsfoot trefoil + Trifolium subterraneum ssp. yaninicum (50:50%); birdsfoot trefoil + Trifolium subterraneum ssp. subterraneum (50:50%). Leaves/stems ratio for alone grown crops was found: birdsfoot trefoil (1.33), Trifolium subterraneum ssp. brachycalicinum (1.02), Trifolium subterraneum ssp. yaninicum (0.93) and Trifolium subterraneum ssp. subterraneum (0.93). Leaves/stems ratio for birdsfoot trefoil in all mixtures was found be higher as compared to alone grown birdsfoot trefoil - by 13.0% for the mixture with Trifolium subterraneum ssp. yaninicum, by 16.3% for that with Trifolium subterraneum ssp. brachycalicinum and by 20.1% for the mixture with Trifolium subterraneum ssp. subterraneum. Total plastid pigments in birdsfoot trefoil increased in all mixtures: with Trifolium subterraneum ssp. brachycalicinum by 7.4%, with Trifolium subterraneum ssp. subterraneum by 8.1% and with Trifolium subterraneum ssp. yaninicum by 15.6%. From mixtures of birdsfoot trefoil were obtained more fixed amount of nitrogen - from 1.71 kg N/da (with Trifolium subterraneum ssp. subterraneum) to 4.84 kg N/da (with Trifolium subterraneum ssp. brachycalicinum) as compared to alone grown birdsfoot trefoil. Birdsfoot trefoil and subterranean clover in mixtures showed good tolerance, morphological and physiological status.