1. Barber, S. A., Walker, J. M. and Vasey, E. H., Principles of ion movement through the soil to the plant root. Intern. Soil. Conf. New Zealand, 121?124 (1962).
2. Beckett, P. H. T., Studies on soil potassium II. The ?immediate? Q/I relations of labile potassium in the soil. J. Soil Sci.15 9?23 (1964).
3. Blanchet, R., Relations entre la vitesse de dilution isotopique du phosphore du sol et l'alimentation phosphatée des plantes. Compt. Rend.244 2739?2741 (1957).
4. Bouldin, D. R., Mathematical description of diffusion processes in the soil-plant system. Soil Sci. Soc. Am. Proc.25 476?480 (1961).
5. Carslaw, M. S. and Jaeger, J. C., Conduction of Heat in Solids-(2nd Edition) Oxford (1959).