1. Andrew, R. H., A technique for measuring root volume in vivo. Crop Sci. 6, 384–386 (1966).
2. Baeyens, J., Les Sols d'Afrique Centrale. Bruxelles, 75–76 (1938).
3. Baeyens, J., Nutrition des Plantes de Grande Culture. Eds. Nauwelaerts, Louvain, 678 p. (1967).
4. Barley, K., The configuration of the root system in relation to nutrient uptake. Advances Agron. 22, 159–201 (1970).
5. Knott, J. E., Handbook for vegetable growers. J. Willey, New York, 245 p. (1966).