Effect of soil properties on soil respiration in cultivated soils with varying organic matter content

The relationship between carbon dioxide (CO2) production in soil respiration and soil carbon (C) content was studied using soil samples from agricultural field parcels where the C content changed along a transect within the field. Incubation of soil samples from 30 sampling points within five fields showed increasing CO2 production with rising soil C content within the range 3-49 %. The amount of CO2 formed in relation to the C content (specific respiration) decreased as the soil C content increased. Thus, diminishing C content of the peat as time passes after drainage does not necessarily lead to proportionally lower emissions and, indeed, our results suggest that the vulnerability of the organic matter to decomposition increases with time since drainage. When divided into classes of mineral soils (0-12 % C), mull soils (12-23 % C) and peat soils (> 23 % C) according to the Finnish national classification, only the mineral and peat soils differed from each other with respect to respiration rate. These results support including mull soils with peat soils when estimating the emissions from organic soils for greenhouse gas inventories. It is also evident that CO2 emissions from some soils classified as mineral soils can be comparable to emissions from organic soils.