YIELD, COMPOSITION, AND IN-VITRO DIGESTIBILITY OF TEMPERATE AND TROPICAL CORN HYBRIDS GROWN AS SILAGE CROPS PLANTED IN SUMMER

Following the harvest of corn silage crops that were planted in spring , second crops of one temperate and four tropical corn hybrids were pl anted under conditions of minimum tilling in four replications on Augu st 3, 1992 and harvested on October 11, 1992 (yr 1). During the 2nd yr , second crops were planted on July 21, 1993 and harvested on October 19, 1993. Dry matter yields of the hybrids ranked similarly for both y ears but differed among hybrids, ranging from 7800 to 11,430 kg/ha (yr 1) and from 8470 to 13,150 kg/ha (yr 2). The temperate hybrid yielded 20% (yr 1) and 26% (yr 2) less than the lowest yielding tropical hybr id. The proportion of grain in the dry matter (DM) differed across hyb rids, ranging from 14.3 to 32.2% during yr 1 and from 18.0 to 32.4% du ring yr 2. Composition of the DM, excluding grain, also differed for t he hybrids: acid detergent fiber ranged from 38.0 to 42.2% during yr 1 and 40.0 to 48.8% during yr 21 in vitro digestible DM ranged from 60. 9 to 65.1% during yr 1 and from 53.0 to 64.6% during yr 2. The tempera te hybrid was the highest in acid detergent fiber and the lowest in in vitro digestible DM. Lower digestibility during yr 2 was attributed t o disease, which infected 24.9 to 40.4% of the foliage of tropical hyb rids and 84.3% of the temperate hybrid. Whole plant DM digestibilities differed narrowly in yr 1 (68.8 to 70.4%) but differed widely in yr 2 (62.2 to 69.9%). There were important differences among yields and co mpositions of tropical hybrids planted in summer, but all were superio r to the temperate hybrid.