FORAGE QUALITY AND HARVEST INDEX OF CORN HYBRIDS UNDER DIFFERENT GROWING CONDITIONS

Recent studies suggest that grain content may not necessarily predict corn (Zea mays L.) forage quality. Field studies were conducted at two New York locations in 1991 and 1992 to evaluate forage quality differences among commercial corn hybrids across different growing conditions and the relationship between the harvest index (HI) value and forage quality. Twelve hybrids, which ranged in relative maturity from 95 to 116 d, were evaluated in two experiments according to maturity differences. Each hybrid was hand-harvested at the 1/2-milk-line stage or 350 g kg-1 dry matter (DM) concentration to determine DM yield, HI, whole-plant N, neutral-detergent fiber (NDF), acid-detergent fiber (ADF), lignin, and in vitro true digestibility (IVTD). Although the relationship among hybrids for NDF was consistent across three of four site-year comparisons, year x hybrid and location x hybrid interactions existed in one experiment because some hybrids received a killing frost at one location before attaining the 1/2-milk-line stage. In contrast, hybrid interactions for IVTD did not exist, which suggests a consistent relationship among hybrids for digestibility, even if hybrids received a killing frost between the dent and 1/2-milk-line stage. The HI correlated closely with NDF (-0.84 and -0.82) and IVTD (0.79 and 0.63) in both experiments. Likewise, lignin correlated closely with NDF (0.84 and 0.88) and IVTD (-0.76 and -0.79). The data suggest that livestock producers can continue to choose hybrids with high grain content if relatively low fiber and high digestibility are of prime interest.