Harvest management and genotype effects on sunn hemp forage characteristics

Sunn hemp (Crotalaria juncea L.) is an annual legume widely used as cover crop; however, there is potential to use it as forage. The objective of this study was to evaluate forage characteristics of five sunn hemp genotypes (herbage accumulation, nutritive value, N fixation, and nematode control), and beef heifer responses (intake and digestibility) to sunn hemp dietary inclusion. Two experiments were conducted at Ona, FL in 2016 and 2017. In Experiment 1, treatments were the factorial arrangement of five sunn hemp genotypes (AU Golden, Crescent Sunn, Ubon, Blue Leaf and Red Mini) and two harvesting time (60 d after seeding or flowering) in a randomized complete block design. In Experiment 2, treatments were 100% sun hemp hay, 50% sunn hemp–50% bermudagrass [Cynodon dactylon (L.) Pers] hay, or 100% bermudagrass hay diets distributed in a completely randomized design. In Experiment 1, Crescent Sunn had the greatest herbage accumulation [15.2 Mg dry matter (DM) ha−1], N fixation (81 kg N ha−1), and nematode control (80% reduction). AU Golden had the greatest crude protein concentration at 60 d after seeding and flowering (155 and 162 g kg−1, respectively). In Experiment 2, increasing the proportion of sunn hemp in the diet decreased total forage DM intake (1.6, 1.4, and 1.2 as a % bodyweight with 0, 50, and 100% sunn hemp inclusion). Sunn hemp harvested 60 d after seeding is adequate to meet the nutritional requirements of most beef cattle categories but the genotype choice affects herbage accumulation and nutritive value.