Legume Productivity and Persistence Under Different Management Regimes.

The ability of forage legumes to fix N, improve productivity, and increase nutritive value makes them a vital component of temperate pasture systems.  Reduced productivity and persistence has been observed, however, in rotationally grazed pastures.  Our objective was to determine the effect of plant maturity and stocking density on pasture productivity and legume persistence.  Individual paddocks of a mixed grass pasture were over-seeded with either alfalfa (Medicago sativa L.), red clover (Trifolium pretense L.), white clover (Trifolium repens L.), birdsfoot trefoil (Lotus corniculatus L.), or nothing in 2013 and rotationally grazed with Holstein heifers (450 kg mean body weight, BW) in 2014 at a low (78,400 kg BW ha^-1) or high (336,000 kg BW ha^-1) stocking density when mixtures reached a mature or vegetative stage of maturity.  Forage yield and nutritive value were measured at each grazing event.  Legume persistence was measured in the fall by point intercept on two 12-m transects at a 50-cm interval.  When grazed at a mature stage, neutral detergent fiber (NDF) concentration of grass-legume mixtures was greatest in spring and declined in subsequent harvests, while NDF of mixtures grazed at vegetative stage increased from spring to summer, and then declined in fall.  When grazed at a mature stage, all treatments were more productive under low (6840 kg ha^-1) than high (5790 kg ha^-1) stocking density, but when grazed at a vegetative stage, all treatments were more productive under high (7090 kg ha^-1) than low (6430 kg ha^-1) stocking density.  Alfalfa and birdsfoot trefoil had greater persistence under both stocking densities when grazed at a mature stage, while red and white clover generally had greater persistence when grazed at a vegetative stage.  The results suggest that legume species respond differentially to grazing management.