Fig. 4. (a) Theoretical, randomly generated "measured," and fitted soil NO₃^––N concentration distributions; and (b) comparison of the estimated and theoretical distributions of the average source-sink term (SST) in the convection-dispersion equation (CDE), at a time interval T = 10 d and a spatial interval SI = 5–10 cm for different relative error RE = 10%, 20% and 30% of measured nitrate concentrations (Ex. 3).