PERSISTENCE OF SAINFOIN UNDER DIFFERENT GRAZING REGIMES

Sainfoin (Onobrychis viciaefolia Scop.), a non-bloat inducing legume, is well adapted to the calcareous soils of the Southern Great Plains. Poor persistence under some managements has limited its use for grazing. Our objectives were to determine the effect of plant growth stage at defoliation and defoliation intensity on persistence of sainfoin. Nitrogen fertilized (100 kg N ha-1) 'Renumex' sainfoin was grown under irrigation on a Pullman clay loam (fine, mixed, thermic Torretic Paleustoll) near Lubbock, TX. Light (L), medium (M), and heavy (H) grazing intensities were applied at the bud (B), flower (F), and seed shatter (S) stages of growth. Across growth stages, L, M, and H intensities averaged 52, 69, and 87% removal of pre-graze herbage mass, respectively. Over the 2 yr, sainfoin stands declined 20 and 43% when defoliated at the B and F stages under H defoliation intensity. Stands remained above 80% for the L and M intensities. Stands increased from reseeding in the S treatments by 35, 31, and 16% for the L, M, and H defoliations, respectively. Root concentrations of total nonstructural carbohydrates (TNC) began to decrease with the initiation of spring growth, reached their seasonal low in June, and then increased into late summer and autumn. Average TNC for H (130 g kg-1) was less than TNC in roots of L and M (155 g kg-1). Our findings indicate that sainfoin defoliated at the B or F stages of growth under L or M intensities of defoliation may have acceptable stand persistence when grown under irrigation in the Southern Great Plains.