Table 1: Transport, sorption, and root parameters used in the NST 3.0 model to describe P uptake by cottonwood for the 0–120, 0–30, 30–60, and 60–120 cm soil depths.

ParameterUnits0–120 cm0–30 cm30–60 cm60–120 cm

Diffusion coefficient in watercm2 s−1
ΘVolumetric soil water contentcm3 H2O/cm3 soil 0.32 0.32 0.33 0.31
Impedance factorUnitless 0.33 0.33 0.35 0.32
Water uptake at rootcm s−1
Initial solution concentration mol cm−3
Buffer powerUnitless 314 45 477 421
Maximum influx at high concentration mol cm−2 s−1
Solution concentration when influx is 0.5  mol cm−3
Solution concentration when influx is zero mol cm−3
Root radiuscm0.0230.02410.02170.0217
Half distancecm1.050.2130.3782.578
Initial root lengthcm m−33,041,3222,094,524663,672283,126
Root growth ratecm d−14,8126,6316,816991

From Edwards and Huffman [18].