RYEGRASS STRAW COMPONENT DECOMPOSITION DURING MESOPHILIC AND THERMOPHILIC INCUBATIONS

The decomposition of perennial ryegrass straw was examined under mesop hilic and thermophilic temperatures. Thermophilic conditions were used to define the composting process. The change in lipids, sugars, solub le polysaccharides, cellulose, and lignin was determined during a 45-d ay incubation. C, H, O, and N steadily decreased in both temperature t reatments. The lignin content, as measured by the Klason or 72% H2SO4 method, decreased by 10% under mesophilic and 29% under thermophilic c onditions. The Klason lignin C loss was 25 and 39% under mesophilic an d thermophilic incubations, respectively. The changes in element (C, N , H, and O) ratios indicated that 94% of the lignin fraction was alter ed during both low- and high-temperature incubations. The changes in t he lignin-like fraction as shown by elemental ratios were more extensi ve than those indicated by the Klason method, showing that this lignin determination has limited value in describing plant residue decomposi tion. The decomposition of the straw components and the concomitant de gradation of the lignin fraction represent an important decomposition process that facilitates the composting of ryegrass straw with a high C:N ratio.