0645 Yield and nutritive value of photoperiod-sensitive sorghum and sorghum-sudangrass in central Wisconsin

A study was conducted to evaluate the yield and nutrient composition of photoperiod-sensitive (PS) and non-PS forage sorghum, sorghum-sudangrass, and sudangrass compared with corn planted on 2 dates and harvested using single- or multiple-cut harvest strategies at 2 research stations (Marshfield and Hancock), each located in central Wisconsin. At each site, treatments were arranged in a randomized complete block design with 4 replicates. The experiment was analyzed as a split-split-plot design with planting date (early or mid June) designated as the main plot, harvest strategy (single cut or multiple cut) as the subplot, and 8 forage cultivars (corn silage, PS forage sorghum, PS sorghum-sudangrass, forage sorghum, BMR forage sorghum, sorghum-sudangrass, BMR sorghum sudangrass, or PS-BMR sudangrass) designated as the sub-subplot treatment factor. Multiple-cut plots were harvested in late August and early October with single-cut plots harvested only in early October. Data were independently analyzed for each location. Overall, forage yields were numerically greater for Hancock plots compared with Marshfield plots. At Hancock, DM yields were greater for the early compared with late planting date (16,225 vs. 12,080 kg DM/ha; P = 0.014), but there were no effects of planting date at Marshfield (overall mean = 8,228 kg DM/ha; P = 0.90). The lack of response at Marshfield was likely due to delayed germination of early planted plots following heavy rains. At both sites, the single-cut harvest (17,517 kg DM/ha at Hancock and 11,729 kg DM/ha at Marshfield) was greater (P < 0.01) than the multiple-cut harvest system (10,789 kg DM/ha at Hancock and 4,726 kg DM/ha at Marshfield). There were yield differences for variety as well as variety by harvest type interactions (P < 0.01) at both locations. At both sites, the multiple-cut harvest strategy reduced yields of all hybrids. The sorghum-sudangrass and PS sorghum-sudangrass varieties had the greatest numerical yields among the sorghum types tested under both harvest strategies. Reduced yields of varieties harvested using multiple-cut strategies may reflect reduced tillering and regrowth capabilities of certain varieties. Using a single harvest, several sorghum forage types has similar or better forage yields compared with corn silage.