Autumn-Accumulated Tall Fescue and Orchardgrass. II. Effects of Leaf Death on Fiber Components and Quality Parameters

The practice of accumulating late summer and fall forage growth for winter pastures is growing. As temperatures drop in the fall, and as growth rates decline, the percentage of dead leaf material increases. The effects of reduced growth rates, and increased leaf senescence, has a pronounced effect on the quality of accumulated forage. The objective of this research was to determine the relationship between dead leaf content and whole plant digestibility of autumn-saved forage. Field experiments were conducted during 1970–71 on a Beltsville silt loam soil (Typic Fragiudults) to determine the influence of N application and soil temperature on leaf deaths, fiber components, and quality parameters of autumn-saved ‘Ky-31’ tall fescue (Festuca arundinacea Schreb.) and ‘Potomac’ orchardgrass (Dactylis glomerata L.). Nitrogen was applied at either 0, 50 (1970 only), or 100 kg N/ha in late September. In 1971, soil temperatures were maintained at ambient and aproximately 12, 20, and 27 C during the autumn using specially designed field equipment. Forage samples were collected from randomly-selected, previously unharvested areas. These were separated into green and dead leaf fractions and analyzed for fiber components and quality parameters. Neither forage species, N application, nor soil temperature greatly affected neutral detergent fiber, acid detergent fiber, lignin, or silica contents of autumn-saved forages. However, there were trends for high fiber and lignin contents in plants grown on high soil temperature plots and for increased fiber content with time during autumn and early winter. Green leaves had lower levels of neutral and acid detergent fiber, lignin, and silica than dead leaves. During autumn and early winter, the proportion of dead leaves in the pastures increased from approximately 20 to 46% in both years; IVDMD of the green leaf fraction decreased slightly during this period from 89 to 85%. In the dead leaf component, IVDMD remained at approximately 67% in 1970 but increased from 60 to 75% in 1971. Relationships were developed for both years which showed that IVDMD of the pastures decreased by 3.38% (r = −0.8477, P 0.001) and 1.0% (r= −0.3147, P 0.05), respectively, for each increase of 10% in dead leaf content. The data indicate that caution should be exercised when using dead leaf percentages alone to predict forage quality of fall-saved pasture; instability in the IVDMD of the dead leaves appears to be a major factor.