Study on the effects of nitrogen, glucose and plant residues on soil microbial C

The soil microbial biomass is studied as the agent of transformation of both fresh organic inputs to soil and of native soil organic matter itself. Microbial biomass C and organic C were measured in 5 soils selected from 5 long term field cultivation at Bastam area of Shahrood region in Iran. Nitrogen, Glucose and plant residues were used as treatments in a factorial randomized block design with four replications The results were used to discuss the effects of Nitrogen, Glucose and organic C in these soils and the relationships between biomass C and total organic C. This suggests that changes in soil biomass C provide an early indication of changes in total soil organic C following changes in soil management. The dynamics of decomposition and transformation of different substrates (nitrogen, glucose and straw) and the effects of substrate incorporation on the turnover of soil biomass C and the decomposition of soil organic C was studied in 5 soils with different characteristics (e.g. clay content, biomass and organic C contents). From this the mechanisms of priming effects (i.e. accelerated decomposition of soil organic matter following incorporation of substrates) were established. It was also concluded that the measurement of biomass C by fumigation-incubation requires the use of a "control" (unfumigated soil) to estimate the basal respiration (the mineralization of non-biomass organic C) of the fumigated soil during 20, 40 and 60 days of incubations. Soil containing more organic C and receiving larger fresh organic C inputs also have faster rates of soil organic C mineralization, suggesting that the turnover of organic C in such soils is probably faster than in soils containing less organic C and receiving less fresh organic inputs.