“…The availability of large amounts of agricultural, industrial, and municipal wastes makes them an important source of humic material, which could improve the physical and chemical structure of soil. Those wastes may have to be oxidized, digested, ammoniated, etc., in order to increase their nitrogen content and value as fertilizers (Mukherjee et al, 1963;Chakrabartty and Berkowitz, 1969;Kim et al, 1981;Fuertes, 1983;Coca et al, 1984Coca et al, , 1985.…”