Plant Residues Decomposition and Formation of Active Organic Matter in the Soil of the Incubation Experiments

The decomposition and mineralization of various plant residues (oak and aspen leaves, pine needles, small branches and thin roots of trees, aboveground biomass and roots of meadow grasses, aboveground biomass and roots of clover, and straw and roots of barley) were investigated in the laboratory experiments by quantitative measurement of produced C-CO2. The plant residues were mixed with vermiculite or gray forest soil (Greyzemic Phaeozems Albic) and incubated under constant temperature and moisture conditions. After a year of incubation, 25-67% of C-org in plant residues were mineralized. Oak leaves, aboveground mass of meadow grasses, and aboveground mass and roots of clover were characterized by a three-pool structure of organic matter with moderate (0.1 > k(1) > 0.01 day(-1)), slow (0.01 > k(2) > 0.001 day(-1)), and very slow (k(3) < 0.001 day(-1)) mineralization rates, while the other types of plant residues had only a two-pool structure with slow and very slow mineralization rates. An opposite relationship between the decomposition rate and the C : N ratio in the plant residues was found. Poorly decomposable types of plant residues were the main source for particulate organic matter (C-POM) in the soil, while highly decomposable types were the main source for microbial biomass (C-mic). The content of potentially mineralizable organic matter in the soil with plant residues correlated positively with C-POM and with C-mic.