Abstract: | Summary A procedure is put forward for calculating the plant uptake of solutes supplied by diffusion and mass flow to the randomly dispersed roots of a developing root system. The model was tested as follows: (a) for a constant root density, and both transport processes—against a more accurate numerical solution of the same system (b) for an increasing root density, and for supply by diffusion only—by electrical simulation using the analog described in Part I. In both cases, results obtained by the two types of calculation were in close agreement. A less accurate method which includes both supply mechanisms and does not require a computer is presented, and compared with an electrical simulation when there is no mass flow. Agreement is within 20 per cent. The model should be useful for predicting plant nutrient uptake from soil, and may be of special interest to modellers of the whole plant system. re]19720905 Soil Science Laboratory, Department of Agricultural Science ,University of Oxford Present address: Department of Plant Sciences,University of Leeds |