FIG. 4. Simulation of the influence of different degrees of basal root gravitropism on the exploitation of P by bean (Phaseolus vulgaris L.) root systems. The depletion zone of P is represented by diffusion of P to the root with time (Diffusion coefficient 10^–8 cm² s^–1). (A) Bean root systems simulated with different rooting patterns (shallow; Carioca, a cultivar, and deep). (B) Volume of the overlapping exploited zones for the three root system types. (C) P uptake by the three simulated root systems at the end of simulation (320 h), in the case of a stratified soil profile of P (P concentration is higher in the first 20 cm of soil) (from Ge et al., 2000).