Estimating soil C loss potentials from the C to N ratio

Thirty-seven arable soil samples (0–20 cm depth) ranging in clay content from 4 to 40% and in C to N ratio from 8 to 20 were incubated at −100 hPa and 20 °C for 238 days. The CO2-C evolved during days 105–147 and days 0–238 was related to the soil C to N ratio by a power function. We hypothesized the existence of a threshold value for the soil C to N ratio below which CO2-C evolution remains constant. A soil C to N threshold value of 9.7 was estimated for both incubation periods and the function predicted that the CO2-C evolution was halved when the soil C to N ratio approached 14. Data obtained by Springob and Kirchmann [Springob, G., Kirchmann, H., 2002. C-rich sandy Ap horizons of specific historical land-use contain large fractions of refractory organic matter. Soil Biology & Biochemistry 34, 1571–1581.] showed a similar relationship, but with a C to N threshold value of 10.8. We suggest that the relationship established between the C to N ratio of a soil and its CO2-C loss during incubation represents a simple but useful measure for predicting soil C loss potentials on a more general level.