Ryegrass straw component decomposition during mesophilic and thermophilic incubations

The decomposition of perennial ryegrass straw was examined under mesophilic and thermophilic temperatures. Thermophilic conditions were used to define the composting process. The change in lipids, sugars, soluble polysaccharides, cellulose, and lignin was determined during a 45-day incubation. C, H, O, and N steadily decreased in both temperature treatments. The lignin content, as measured by the Klason or 72% H₂SO₄ method, decreased by 10% under mesophilic and 29% under thermophilic conditions. The Klason lignin C loss was 25 and 39% under mesophilic and thermophilic incubations, respectively. The changes in element (C, N, H, and O) ratios indicated that 94% of the lignin fraction was altered during both low- and high-temperature incubations. The changes in the lignin-like fraction as shown by elemental ratios were more extensive than those indicated by the Klason method, showing that this lignin determination has limited value in describing plant residue decomposition. The decomposition of the straw components and the concomitant degradation of the lignin fraction represent an important decomposition process that facilitates the composting of ryegrass straw with a high C:N ratio.