SimRoot has been out for a couple years now. Developed by Penn State, PSU is a leader in understanding root architecture.
In the SimRoot video shown below, Nitrogen uptake is modeled. Note how the root hairs closest to the surface take in the most available nitrogen.
When designing nature irrigate, native plant green roofs it is essential to capture as much rainwater and water vapor as possible, for irrigation and for scavenging dissolved nutrients.
Check out the following SimRoot Video by PennState!