1. Barber, SA (1984) Soil nutrient bioavailability; A mechanistic approach. New York, John Wiley and Sons.
2. Barber, SA, Cushman, JH (1981) Nitrogen up take model for agronomic crops. In: Iskandar, IK, ed, Modelling wastewater renovation-land treatment, pp. 383–409. New York, Wiley-Interscience.
3. Johnson KD (1981) Tall fescue (Festuca arundinacea Schreb) root relationships. Ph.D. diss. West Lafayette, IN, Purdue University.
4. Jonsson, K, Fidjeland, L, Maghembe, JA, Hogberg, P (1988) The vertical distribution of fine roots of five tree species and maize in Morogoro, Tanzania. Agroforestry Systems 6: 63–69.
5. Mengel, DB, Barber, SA (1974) Development and distribution of the corn root system under field conditions. Agron J 66: 341–344.