Does Nitrogen Applied to Crop Residues Produce More Humus?

Abstract The fate of carbon in carbonaceous crop residues decomposing under different levels of nitrogen is considered. Laboratory and greenhouse results show that although nitrogen additions offset the harmful effect of such residues on crop growth, and often accelerate decomposition, such added nitrogen does not appreciably increase the percentage of the crop residue carbon that remains in the soil as humus. Nitrogen added to cropped soils does tend to maintain soil organic matter at a higher level than in its absence, but this is due to the increased crop yields and resulting larger, crop residues available for humus formation.