Nitrogen will be linked to higher organic matter content, possible variation in the ratio between C and N means that this relationship is not so clear-cut. Qian et al. (1993) found colour to be a strong predictor of soil N content in mineral forest soils, but found that a number of possible factors were important in the relationship. However, when we include the fact that the C:N ratio was also relatively well predicted
from colour it is not a surprise that N is predicted well. However, this does leave us with the problem of explaining why the ratio between C and N could be related to soil colour. Different soil organic matter pools are known to have different C:N values, with pools that are more labile having a higher C:N value and containing more of the colour of the original plant material (this is in reference to the commonly-used
terms for pools of organic matter in soil, e.g. Decomposable Plant Material (DPM), Resistant Plant Material (RPM) etc., and not to the C:N values for different raw materials, where lower C:N values imply more labilematerial).