C d), T s -base temperature at which f Nmin (t) equals 1 ( o C), T soil -daily mean soil temperature (ºC), U N -potential N uptake (kg ha -1 ), U Nr -potential N demand by fibrous roots (kg ha -1 ), W -dry weight of the entire plant excluding fibrous roots (t ha -1 ), W r -dry weight of fibrous roots (t ha -1 ), Z osmo -soil depth used in the calculation of mean osmotic pressure (cm), Z smin -depth of soil below which no N mineralization is assumed to take place (cm), ΔW r -root dry weight increment (t ha -1 ).