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 differ ences among commercial corn hybrids across different growing condition s 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 differ ences. Each hybrid was hand-harvested at the 1/2-milk-line stage or 35 0 g kg-1 dry matter (DM) concentration to determine DM yield, HI, whol e-plant N, neutral-detergent fiber (NDF), acid-detergent fiber (ADF), lignin, and in vitro true digestibility (IVTD). Although the relations hip among hybrids for NDF was consistent across three of four site-yea r comparisons, year x hybrid and location x hybrid interactions existe d in one experiment because some hybrids received a killing frost at o ne location before attaining the 1/2-milk-line stage. In contrast, hyb rid interactions for IVTD did not exist, which suggests a consistent r elationship among hybrids for digestibility, even if hybrids received a killing frost between the dent and 1/2-milk-line stage. The HI corre lated closely with NDF (-0.84 and -0.82) and IVTD (0.79 and 0.63) in b oth experiments. Likewise, lignin correlated closely with NDF (0.84 an d 0.88) and IVTD (-0.76 and -0.79). The data suggest that livestock pr oducers can continue to choose hybrids with high grain content if rela tively low fiber and high digestibility are of prime interest.