1. Determination of extracellular and intracellular enzymes in soil by treatment with ultrasound and subsequent differential centrifugation;Aliev;Moscow Univ. Soil Sci. Bull.,1975
2. Influenza degli zuccheri e degli acidi organici sull'idrolisi delle proteine;Anelli;Sci. Tecnol. Alimenti,1973
3. Methods of Soil Analysis;A.S.A.,1965
4. Soil Nitrogen;Bremner,1965
5. Concerning the location and persistence of soil urease;Burns,1972