Humification of Rice and Wheat Residues in Soil

Humification of carbon (C) added through crop residues was investigated in the laboratory at 25±2°C and 40±2°C and at 60 per cent water holding capacity of the soil About 29.0 to 43.4 per cent of applied C through rice straw and 24.8 to 39.5 per cent through wheat straw was decomposed to CO₂ in 60 days period. Humic acid (HA) fraction accumulated 23.7 to 41.2 per cent of the carbon applied through rice residues and 14.4 to 38.3 per cent through wheat straw. Humin (Hn) fraction of organic matter retained 10.6 to 28.6 per cent and 20.4 to 45.0 per cent carbon of rice and wheat straw, respectively. Application of nitrogenous compounds increased the decomposition of crop residues, decreased the C content of HA and increased the C content of th Hn. The nitrogen contents of HA and Hn fractions were increased by applying fertilizer N alone and along with crop residues.