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.

Parameter Units 0–120 cm 0–30 cm 30–60 cm 60–120 cm Diffusion coefficient in water† cm2 s−1 Θ Volumetric soil water content cm3 H2O/cm3 soil 0.32 0.32 0.33 0.31 Impedance factor Unitless 0.33 0.33 0.35 0.32 Water uptake at root cm s−1 Initial solution concentration mol cm−3 Buffer power Unitless 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 radius cm 0.023 0.0241 0.0217 0.0217 Half distance cm 1.05 0.213 0.378 2.578 Initial root length cm m−3 3,041,322 2,094,524 663,672 283,126 Root growth rate cm d−1 4,812 6,631 6,816 991

†From Edwards and Huffman [18].