1. Al-Faiyz, Y.S.S. 2017. CPMAS 13C NMR characterization of humic acids from composted agricultural Saudi waste. Arabian Journal of Chemistry 10: 839–853.
2. Anonymous. 2013. Technical evaluation report. Compiled by Pesticide Research Institute for the USDA National Organic Program, 1–3.
3. Asing, J., N.C. Wong, and S. Lau. 2009. Optimization of extraction method and characterization of humic acid derived from coals and composts. Journal of Tropical Agriculture and Food Science 37(2): 211–223.
4. Bremner, J.M. 1996. Nitrogen-total. In Methods of soil analysis. Part 3, Chemical methods, ed. D.L. Sparks, A.L. Page, P.A. Helmke, and R.H. Loeppert, 1085–1121. Madison, WI: Soil Science Society of America, American Society of Agronomy.
5. Busato, J.G., D.B. Zandonadi, L.B. Dobbss, A.R. Façanha, and L.P. Canellas. 2010. Humic substances isolated from residues of sugar cane industry as root growth promoter. Scientia Agricola 67: 206–212.