Effects of Sample Drying Procedure on Chemical Composition and In Vitro Digestibility of Coastal Bermudagras

‘Coastal’ bermudagrass (Cynodon dactylon L.) grown under three levels of N-K fertilization and three growth intervals was air-dried at 23C and over-dried at 57C, 75C, and 100C to determine sample-drying effects on cell wall constituents (CWC), acid-detergent fiber (ADF), acid-detergent lignin (ADL), and in vitro digestibility. Heat-dried samples were compared with quick-frozen, freeze-dried samples from the same plots. Levels of N-K fertilization were 224-112, 672-336, and 1,120-560 kg N-K/ ha per year, and growth intervals were of 2-, 4-, and 6- week durations under irrigated conditions. Oven-drying increased CWC, ADF, and ADL contents of forage over those of freeze-dried forage. Cell wall constituents were increased most at drying temperatures of 75C or above, with CWC content of immature samples being increased relatively more than that of mature samples. Acid-detergent fiber content and ADL content were significantly increased by longer growth intervals, with one exception—ADL content of 2-week-old samples dried at 100C was similar to that of 6-week-old forage. In vitro digestibility expressed as percent dry matter disappearance was greatest in freeze-dried samples and least in air-dried samples. Growth interval and sample-drying interacted in that 2-week-old, OD-100C forage had similar digestibility to 4-week-old quick-frozen, freeze-dried forage. Differences in in vitro digestibility between the QF-FD, OD-75C, or OD-57C were small and nonsignificant. Forage samples oven-dried to constant weight at temperatures of 75C or less in 48 hours gave results representative of the agronomic treatment effects comparable to those of the quick-frozen, freeze-dried samples. Cells wall contituent fractions appeared most affected by oven-drying; however, even though changes in response to growth interval and N-K level were reduced by oven-drying, interpretation of treatment differences were consistent.