DROUGHT EFFECTS ON PERENNIAL FORAGE LEGUME YIELD AND QUALITY

Drought frequently limits alfalfa (Medicago sativa L.) herbage productivity during mid-summer in the North Central USA, but the productivity of other legumes during drought is unknown. We determined the effect of drought on the herbage yield and quality and stand persistence of birdsfoot trefoil (Lotus corniculatus L.), cicer milkvetch (Astragalus cicer L.), red clover (Trifolium pratense L.) and alfalfa. Legumes were established on a sandy, mixed, Udorthentic Haploborolls and subjected to two soil water regimes promoting 'droughted' and 'well-watered' (control) plant growth. Mid-day stem pressure potentials for droughted and control plants ranged from -1.3 to -3.8 MPa and -0.1 to -1.4 MPa, respectively. When drought occurred throughout growth, legume herbage yields of droughted alfalfa, birdsfoot trefoil, cicer milkvetch, and red clover averaged 33, 21, 19, and 13% of their respective controls. Average herbage yield of droughted alfalfa was 120% greater than yields of birdsfoot trefoil and cicer milkvetch, and 165% greater than red clover yield. Averaged for all harvests and species, whole herbage acid detergent fiber (ADF), neutral detergent fiber (NDF), and acid detergent lignin (ADL) concentrations were reduced by 30 to 48%, 26 to 46%, and 0 to 49%, respectively, when drought occurred throughout growth. Effects of drought on lignin in NDF and crude protein concentration were not consistent. Droughted alternative legumes produced herbage with lower ADF, NDF, and ADL concentrations than alfalfa. Improved quality in droughted legumes was related to greater leaf:stem weight ratio, delayed maturity, and often higher quality in both the leaf and stem fractions compared to the control treatment. Although drought reduced the herbage yield of all legumes, alfalfa has the greatest yield potential in drought.