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item Sinclair, Thomas
item Ray, Jeffery - Jeff
item Mislevy, Paul
item Premazzi, L.

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2002
Publication Date: 3/1/2003
Citation: Sinclair, T.R., Ray, J.D., Mislevy, P., Premazzi, L.M. 2003. Growth of subtropical forage grasses under extended photoperiod during short-daylength months. Crop Science. 43:618-623.

Interpretive Summary: Forage grass yields in the southeastern U.S. during the winter months can be severely limiting in cattle production. This seems especially true in the more southerly regions where temperatures are usually sufficiently warm to allow grass growth through the winter months. This paper, written by USDA, ARS scientists located at Gainesville, FL and Stoneville, MS, explores the hypothesis that grass growth during the winter months is regulated to decrease as a result of the short daylengths that exists during these months. To demonstrate that growth was constrained by daylength, lights were erected over field plots to extend the daylength to 15 hours. The results of this experiment did indeed, show that grass growth could be sustained during the winter months simply by eliminating the control resulting from the short daylength. Winter yields in two of the grasses were increased two and three fold. Continued growth in the winter months did not result in any negative consequence on subsequent spring grass growth, or the quality of the forage. This experiment indicates that the genetic introduction of daylength insensitivity into these forage grasses could lead to substantial yield increases during winter months.

Technical Abstract: One constraint on cattle production in southeast USA is low productivity of forage grasses during the short-daylength months. Evidence indicates that loss of total growth during these months could be lessened by exposing grasses to extended photoperiod. A detailed analysis of their year-round productivity and nutritive value is needed to fully understand the consequences of overcoming the photoperiod-induced decline in growth. A 2-y experiment was established at Ona, FL in which photoperiod was extended to 15 h throughout the short-daylength months. Four grasses were studied: Pensacola bahiagrass, Paspalum notatum Flugge var. Saurde Parodi; Tifton 85 bermudagrass, Cynodon spp. L.; Florakirk bermudagrass, Cynodon dactylon L.; and Florona stargrass, Cynodon nlemfuensis Vanderyst var. nlemfuensis. Growth increases were observed in all grasses during the short-daylength months as a result of the extended-photoperiod treatment with increases in the January through March harvests of 3-fold or more for Pensacola bahiagrass and 1.5- to 2.5-fold for Tifton 85 bermudagrass. Generally, there was no evidence of adverse consequences from sustained growth during the short-daylength months.