Growth Stage at Harvest Influences Forage Quality and Yield of Brown Midrib Forage Sorghum

Forage sorghum (Sorghum bicolor L.) can be a viable alternative to corn silage (Zea mays) in double cropping rotations with winter cereals in the northeastern US. Given a relatively short summer, a late September or early October harvest of sorghum is ideal for the rotation. Our objective was to determine the impact of harvest timing on quality and yield of forage sorghum. Sorghum was harvested weekly for nine weeks in 2015, from boot through hard dough at two locations in central NY. In 2016, a rotation trial with forage sorghum and triticale (x Triticosecale) was initiated in Aurora, NY, to evaluate the impact of timing of sorghum harvest (2-week interval; four timings) on quality and yield. Quality parameters that were measured included crude protein (CP), rumen degradable protein (RDP), acid detergent fiber (ADF), neutral detergent fiber (NDF), lignin, acid detergent lignin (ADL), starch, non-fiber carbohydrates (NFC), NDF digestibility (30 hr, NDFD₃₀), and in vitro true 30 hr digestibility (IVTD₃₀). Yields increased from 14.6 and 12.2 Mg DM ha^-1 at flowering to 16.6 and 23.4 Mg DM ha^-1 at milk stage (late September/early October) for 2015 and 2016, respectively, with no further yield gain beyond milk stage in either year. Between milk and soft dough in 2015, freshly dried samples decreased in CP, RDP, NDF, and NDFD₃₀ as plants matured, while ADL, starch, and NFC increased. In the 2016 study, for freshly dried samples, NDF, ADF, IVTD₃₀, and NDFD₃₀ decreased with plant maturity while ADL increased. Ensiled samples in 2015 between milk and soft dough were higher in CP, RDP, ADL, and ADF and lower in starch, NDF, and NDFD₃₀ than the freshly dried samples. In 2016, the ensiled samples followed a similar pattern to the freshly dried samples, however ADL and NDF were slightly lower at the soft dough stage. These data suggest that harvest of forage sorghum as early as milk stage optimizes yield and most forage quality parameters, enabling more timely planting of winter cereals. However, harvest at milk stage will result in lower starch and higher moisture content than forage harvested at soft dough. Additional work is ongoing to determine the feed quality of forage sorghum when harvested at milk stage.