COMPOSITION OF THE ROOTS AND STUBBLE OF PERENNIAL RYEGRASS FOLLOWING PARTIAL DEFOLIATION

Abstract

When the foliar portion of a grass plant is removed by a mower or by a grazing animal, the growth of new tissues is initiated to replace the parts removed. The rate with which the regeneration of new top growth proceeds and the total amount produced are of great importance in forage production. This rate of recovery and total yield, although dependent to a large extent upon external environmental factors, are also influenced considerably by the intensity and frequency of defoliation as determined by management practices. Evidence has been offered by many workers (5, 9, 10, 11, 21, 23, 24, 26, 29) that close and frequent clipping or grazing reduces the total yield of tops of forage plants. Associated with the ability of the plant to produce new growth after cutting is its chemical composition. Plants cut less frequently and less severely have a greater opportunity to synthesize and maintain reserve food materials which are available for the production of new growth than plants more severely grazed. That carbohydrates are important as reserve substances in pasture plant economy has been pointed out by earlier workers (1, 4, 7, 8, 13, 14, 15, 16, 25, 27, 28). The specific carbohydrates which may be considered reserves that can be utilized by the plants for purposes of respiration and production of new tissues have not been definitely established. Weinmann (27) considered that sugars and polysaccharides hydrolyzable by hot dilute HCI were lost from the tops of some South African grasses after the time of flowering and were largely recovered in the roots. In another contribution (28), the seasonal changes in the composition of roots were described as mainly due to translocation and storage. Sugars and starch (polysaccharides rendered soluble by saliva and hydrolyzed by HCI) were considered of importance but the results with total hydrolyzable polysaccharides were not conclusive and were not reported. In alfalfa, Albert (2), Graber, et al. (8), and Leukel (13) considered sugars, dextrins, starch, and hemicelluloses as available carbohydrates and found that the supply of these in the roots was lowered by frequent cutting of the immature tops. Plants in darkness (2, 8) produced new top growth while starch disappeared from the roots; total carbohydrates decreased and hemicelluloses increased. According to Bukey and Weaver (4) there was a marked decrease in the percentage of invert sugar, water-soluble hydrolyzable, and water-insoluble hydrolyzable ? Contribution no. 48, of the U. S. Regional Pasture Research Laboratory, Division of Forage Crops and Diseases, Bureau of Plant Industry, Soils and Agricultural Engineering, Agricultural Research Administration, U. S. Department of Agriculture, State College, Pennsylvania, in cooperation with the northeastern states. 656