AbstractForage sorghums Millo Blanco (MB) [Sorghum bicolor (L.) Moench] and ATx623 x MB (photoperiod sensitive) (PS) and Greenleaf (GL) sudangrass [S. sudanense (Piper) Stapf] and ATx623 x GL (photoperiod insensitive) (PE) were planted the 15th day of each month over a period of two years at the Isabela, P.R., USDA-ARS farm. Two consecutive 60-d harvests were made for each planting during a period of two years. Mean annual dry matter yield (DMY) in t/ha was 32 for ATx623 x MB, 29 for MB, 26 for ATx623 x GL, and 20 for GL. On the average, the PS genotypes had significantly higher DMY (32%) than the PI genotypes; and produced significantly more DM (96%) when planted in June than when planted in December. ATx623 x GL and ATx623 x MB significantly surpassed their male parents in DMY (33 and 11%). Mean forage crude protein (CP) of the genotypes was 11%. Significantly more crude protein yield (CPY) was obtained when the PS genotypes were planted during long days. Genotypes planted during short days were shorter. In most cases, leaf area was greater for the June to August plantings. Planting date (PD) had no significant effect on the in vitro dry matter digestibility (IVDMD) of the genotypes; the overall mean was 56%. This research demonstrated that DMY of more than 7 t/ha with a CP of 11% and IVDMD of 56% can be obtained in a 60-day growth period from a forage sorghum such as MB or ATx623 x MB planted during long days (June) in Puerto Rico. Results showed the advantage of planting PS lines and hybrids for forage production in Puerto Rico.
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