Harvest Frequency and Cutting Height Affect Herbage Accumulation and Nutritive Value of Sunn Hemp.

Cool-season perennial forages, such as tall fescue become dormant and less productive during summer. We need to identify warm-season forages that improve nutritive value and yield of fescue-based forage-livestock systems during this period. Crotalaria juncea L. (sunn hemp; SH) is a fast-growing, warm-season tropical legume that can fill this void. Our objectives were two-fold: to evaluate nutritive value of SH and SH silage harvested at 35, 45, and 55 days after planting (DAP) and to determine yield and regrowth potential when harvested at 10 and 15 cm cutting heights at each harvest interval. Crude protein was greatest (P<0.05) in SH silage (157 g/kg DM) followed by pre-ensiled SH (140 g/kg DM) at 35 DAP. Crude protein was lowest for pre-ensiled SH (85 g/kg DM) and SH silage (93 g/kg DM) harvested at 55 DAP. Neutral-detergent fiber was greatest (P<0.05) for SH silage at 55 and 45 DAP (544 and 542 g/kg DM, respectively). Neutral-detergent fiber was lowest (P<0.05) for pre-ensiled SH (304 g/kg DM) and SH silage (292 g/kg DM) harvested at 35 DAP.  Acid-detergent fiber was greatest (P<0.05) in SH silage at 45 and 55 DAP (451 and 446 g/kg DM, respectively). Acid-detergent fiber was lowest (P<0.05) for pre-ensiled SH (202 g/kg DM) followed by SH silage (239 g/kg DM) harvested at 35 DAP. Overall DM yield was greatest (P<0.05) at 55 DAP followed by 45 and 35 DAP. The greatest regrowth potential (P<0.05) was observed at 35 DAP regardless of harvest height (10 cm = 1.5 Mg/ha; 15 cm = 2.1 Mg/ha). Nutritive value of SH decreased with increasing DAP, and silage CP was greater than pre-ensiled at each harvest. Our results suggest that nutritive value and yield of SH and SH silage can be optimized by initially harvesting at 35 DAP and harvesting again following a 20-d period of regrowth.