SUSTAINABLE YIELD INDEX IN SOME MIXTURES

Abstract

Sustainable yield index (SYI), nitrogen in dry aboveground mass yield and amount of fixed nitrogen of birdsfoot trefoil, sainfoin and subterranean clover pure grown and in mixtures with tall fescue in the next ratios: birdsfoot trefoil + tall fescue (50:50), sainfoin + tall fescue (50:50), subterranean clover + tall fescue (50:50), birdsfoot trefoil + subterranean clover + tall fescue (33:33:33), sainfoin + subterranean clover + tall fescue (33:33:33) were studied. Pot trial was carried out in the Institute of Forage Crops, Pleven, Bulgaria during 2011-2012. SYI in pure grown birdsfoot trefoil (0.767), sainfoin (0.720) and subterranean clover (0.666) was calculated. Sustainable yield index (SYI) in mixtures was found be higher - from 9.6% (sainfoin+tall fescue) to 18.2% (subterranean clover + tall fescue). Birdsfoot trefoil accumulated the highest amount of fixed nitrogen in dry aboveground biomass (8102 mg N/kg DM), followed by subterranean clover (6730 mg N/kg DM) and sainfoin (5598 mg N/kg DM). On averaged from mixtures studied nitrogen in dry aboveground biomass (7540 mg N/kg DM) was found be higher by 10.7% as compared to pure grown crops (6810 mg N/kg DM). Amount of fixed nitrogen obtained from mixtures (95.64 mg/kg DM) was by 15.2% higher as compared to pure grown forage legumes (81.79 mg/kg DM). Parameters as sustainable yield index, nitrogen in dry aboveground biomass, amount of fixed nitrogen were found be higher in mixtures.