1. Barber, D. A. and Lynch, J. M., Microbial growth in rhizosphere. Soil Biol. Biochem.9, 305–308 (1977).
2. Blue, W. G., Gammon, N. Jr. and Winsor, H. W., Accumulation of organic matter and nitrogen in Flatwoods soils planted to white clover-grass. Soil Crop Sci. Soc. Fla.24, 20–26 (1964).
3. Clement, C. R. and Williams, T. E., Leys and soil organic matter, II. The accumulation of nitrogen in soils under different leys. J. Agric. Sci. Camb.69, 133–138 (1967).
4. Haider, K., Martin, J. P. and Filip, Z., Humus Biochemistry.In E. A. Paul and A. Douglas McLaren (Eds.), Soil Biochemistry3, Marcel Dekker, Inc., New York, pp. 195–244 (1975).
5. Harmsen, G. W., Die Bedeutung der Bodenoberfläche für die Humusbildung. Plant and Soil3, 110–140 (1951).