1. Humic materials for agriculture;Mikkelsen;Better Crop.,2005
2. Humus, Origin, Chemical Composition, and Importance in Nature;Waksman,1938
3. Oxidized Lignites and Extracts from Oxidized Lignites in Agriculturehttp://humates.com/Humates in Agriculture - Karr.pdf
4. Mitigating activity of humic substances: Direct influence on biota;Kulikova,2005
5. Commercial humates for agriculture and the fertilizer industry