Fig. 3. Net nitrification rates (NR) per mass soil in (a) mineral and (b) organic horizon soils versus NR predicted from multiple regression models in the form of Eq. [1] with = 2. Regression coefficients (a_i) shown for each independent variable (A_i) in order of decreasing importance to overall model. _r = relative water content; C/N = kg C per kg N; M_r = net N mineralization rate (mg N kg^-1 d^-1); N = g N per 100 g soil; C = g C per 100 g soil. * signifies p < 0.05; ** signifies p < 0.01; *** signifies p < 0.001.