1. Role of microorganism metabolites in the formation of humus substances;Alexandrova;Pochvovedenie,1968
2. Studies on soil humic acids. I.The chemical nature of humic nitrogen;Bremner;J. agric. Sci., Camb.,1955
3. Organic forms of nitrogen;Bremner,1965
4. Chemische Untersuchungen an Humusstoffen;Flaig;Z. Chem.,1964
5. Humusstoffe;Flaig,1966