Humification of straw at different nitrogen levels followed by acriflavine adsorption and light absorption

Summary Humic compounds isolated from decomposing wheat and rye straw, incubated for different periods with and without nitrogen added, were investigated for their acriflavine adsorption capacity and light absorption property. In the first instance, it was established that the degree of dyestuff adsorption on the acid-precipitable humic compounds is correlated with the extent in optical density of the total humus extracted by weak alkaline solution. Furthermore, the influence of nitrogen added on the rate of humification could be followed closely by the adsorption and absorption characteristics. It was demonstrated that the initially increased rate of humus formation, achieved by the addition of nitrogen, was compensated for by a decrease of such compounds when the experimental period was extended. It seems, that humic substances, after exhaustion of the easily available carbon and nitrogen sources, may again play a role in the metabolic cycle of the micro-organisms.