Distribution of roots with depth

Depth distribution of roots, r(z), can be defined either as a fraction of roots in each horizon according to parameter values (table) or as a function (uniform, linear or exponential) of depth (see switch RootDistribution). In a similar way to the uniform and linear function the exponential form is normalized making the integral of the whole soil profile equal to unity. The fraction of roots (root density) below a depth z is given by:

                                                      (3.9)

where it can be shown that the exponential extinction coefficient k_rr equals -ln(r_frac). r_frac is a parameter.

If the distribution of roots is defined as parameter values, these values should be specified in the parameter table Root distribution with depth.