Figure 4.
Comparison of observed and predicted P uptake, total dry matter (TDM), and root dry matter (DMr) for three sub-models that differ in complexity of the P uptake process. The one-step model assumes roots take up P at a constant rate regardless of root age, whereas the two-step model assumes that newly formed roots have higher P uptake because they grow into soil not yet depleted of its available P. The three-step model adds a third uptake element. After new roots have depleted readily available P and before they have reached full maturation characterized by very low uptake, roots are considered to actively influence rhizosphere processes, providing additional P for uptake.