1. De Nobili M, Cercignani G and Leita L 1984 Evaluation of type and contents of humic substances in sludges and compost.In Long-Term Effects of Sewage Sludge and Farm Slurries Applications. Elsevier Applied Science Publishers, London, pp 204–209.
2. De Nobili M, Cercignani G, Leita L and Sequi P 1986 Evaluation of organic matter stabilization in sewage sludge. Commun. Soil Sci. Plant Anal. 17, 1109–1119.
3. Roletto E, Barberis R, Consiglio M and Iodice R 1985 Chemical parameters for evaluating compost maturity. Bio-Cycle 26, 46–47.
4. Schnitzer M, Lowe L E, Dormaar J F and Martel V 1981 A procedure for the characterization of soil organic matter. Can. J. Soil Sci. 61, 517–519.
5. Sequi P, De Nobili M, Leita L and Cercignani G 1986 A new index of humification. Agrochimica 30, 175–179.