Influence of methods of determination, and time of day, on contents of nonstructural carbohydrates in grazed ryegrass—clover herbage from a nitrogen-fertilised pasture

Abstract

Different methods for estimating contents of nonstructural carbohydrates in grazed ryegrass-white clover herbage from a pasture fertilised with nitrogen were investigated in some detail and compared; with all methods, a Somogyi copper reagent was used for the final titration of reducing sugars. Extraction with cold water, and then hot water, and subsequent hydrolysis of the extracts with dilute H₂SO₄ gave results that generally agreed with those obtained with a method using an initial extraction with aqueous ethanol, and one using enzymatic hydrolysis with amyloglucosidase. The amount of carbohydrate soluble in hot water, but insoluble in cold water, was taken as an indication of the content of starch; other methods tor determining starch were also investigated. Some advantages and limitations of the above procedures are discussed. The water-extraction method was subsequently adopted for routine use in a more comprehensive investigation of the influence of nitrogen fertiliser on the chemical components of grass-clover herbage, The levels of total nonstructural carbohydrates in all of the samples of grass-clover herbage were low. In a time-of-day experiment, samples taken in mid morning had less (9–11%) total water-soluble carbohydrates than those taken in rather late morning (11–13%) or mid afternoon (11–14%); the fraction soluble in hot water, but insoluble in cold water, corresponded to 0.6–0.8%, 0.7–0.9%, and 0.9–1.1% respectively.