The effects of forest plant residue type and nitrogen application on organic carbon and nitrogen dynamics

Forest ecosystems are very important types of land uses for storage of carbon in soils and removal of the atmospheric carbon dioxide. Forest plant residues which decompose slowly have a longer residence time and cause more storage of carbon in soils. As an ecological process, litter decomposition provides plants with nutrients for growth and influences their net dry primary products. The aims of this research were to study the effects of forest plant residue type and nitrogen application on organic carbon mineralization.
This experiment was performed to evaluate the effects of forest plant residue type and nitrogen application on organic carbon and nitrogen dynamics. A split – split plot experiment with three replications was conducted using the litter bag method. The examined factors included types of plant residue (oak, bald cypress, white poplar and pine), levels of applied nitrogen (0, 20 and 40 mg N / kg soil) and incubation periods (1, 2, 3 and 4 months) which were located in sub – sub, sub – and main plots respectively. At the end of the incubation period, the litter bags were pulled out of the pots; after the weights of the remaining plant residues in the bags were measured, the plant residues organic carbon was measured via the dry combustion method at 450°C for 5 h and the total nitrogen via the kjeldahl method. Organic carbon and nitrogen losses were calculated by subtracting the remaining amounts of organic carbon and nitrogen at each incubation time interval from those of the prior interval.
The greatest (52.89 %) and the least (25.77%) amounts of organic carbon loss were measured respectively for white poplar and oak plant residues. White poplar plant residue also showed the greatest (42.74%) amount of nitrogen loss during incubation which was in contrast to pine plant residue which had the least (31.03%) amount of nitrogen loss. The highest and lowest amounts of organic carbon and nitrogen loss were obtained from 40 mg N / kg soil and control treatment. The amounts of organic carbon and nitrogen losses increased as the incubation period increased but the highest amounts of organic carbon and nitrogen losses were measured for the first month of incubation.
Application of nitrogen causes an increase in the residual organic carbon and nitrogen loss. White poplar residues have a higher decomposition rate than those of oak because they contain less amounts of lignin, as poplar is a soft wood tree.