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Grazing of tropical grasses represents the most common forage source used for ruminant nutrition in Puerto Rico. However, because of limited land availability for agricultural purposes and periodic extended drought during recent years, many dairy producers have adopted the use of total mixed rations (TMR) as a feeding system for dairy cattle. Low yield and poor nutritive value of tropical grasses represent one limitation of this feeding method. Therefore, the evaluation of high yielding forages with potential for use in silage production represents an urgent need. Corn (Zea mays L.) is the most frequently used forage source in TMR in temperate environments. Knowledge about the agronomic and ensiling characteristics of corn hybrids planted, harvested and ensiled in tropical environments will enable selection of the most appropriate varieties. This research was designed to determine yield (dry matter basis), fermentation characteristics and aerobic stability of silages made from two corn hybrids. An experimental planting of the two corn hybrids, Dekalb DKC 67-60 and Dekalb DKC 69-71, was carried out for the stated purpose. Research plots (50 X 50 m) were established at the Agricultural Experimental Sub-station located in Lajas, Puerto Rico. The two commercial corn hybrids evaluated were replicated four times in the plots. Research plots were irrigated as needed to ensure germination and no weed control was needed. Lannate Pw (Metomil-S-metil N-metilcarbamil oxitioacetamidate) was sprayed (0.3 kg ai/ha) with a pressure sprayer at 35 days after corn emergence to control fall army worm [Spodoptera frugiperda (Smith)]. Measurements of plant density (number of plants per hectare) were taken at 28, 37 and 90 days after planting. Forage dry matter yield and cob length (cm) was measured only after 90 days. Statistical analysis for the agronomic characteristics was appropriate for a randomized block (corn hybrids) design (Steel and Torrie, 1980). To study the ensiling characteristics, we harvested a subsample of planted corn after 77 days of growth and ensiled it in lab-scale microsilos (1.2-kg capacity). Triplicate samples of each hybrid were analyzed to determine initial (prior to ensiling) chemical composition using standard procedures (AOAC, 1990; Van Soest et al., 1991). Three silos of each corn hybrid were opened after 45 days of fermentation and silage samples were analyzed to determine pH, and fermentation end-products (organic acids). Statistical analysis of the ensiling characteristics was according to a randomized design with a 2 (Dekalb corn hybrids) by 2

SILAGE YIELD, FERMENTATION CHARACTERISTICS AND AEROBIC STABILITY OF TWO CORN HYBRIDS