CHARACTERISTICS OF LABORATORY-PREPARED HUMIFIED ORGANIC-MATTER AS AFFECTED BY THE COMPOSITION OF STARTING MATERIALS

Laboratory humification experiments were carried out at 27°C and 95 percent relative humidity starting from sawdust, either alone or mixed with different materials, and using watered soil extract as a primer. Increasing yields of humified matter were obtained by the following additions: NH4NO3< sawdust alone < NH4NO3+ sucrose < NH4NO3+ CaCO3< sucrose < CaCO3< NH4NO3+ CaCO3+ sucrose < CaCO3+ sucrose < casein + sucrose < casein + CaCO3+ sucrose < casein < casein + CaCO3. Also, the most favorable molecular size distribution of the humic fractions, with reference to the promotion of the stability of soil structure and to the efficiency of nutrient uptake by roots, was that obtained by incubation of sawdust with casein + CaCO3. © 1979 The Williams & Wilkins Co.