This paper reports on experiences with the use of the PEST (Parameter ESTimation) programme to calibrate the soil physical parameters of a nitrate leaching model (the Burns alpha model) and to determine the N mineralization rate by inverse modelling. Parameter estimation was much more efficient and accurate with the PEST programme than with a built in "trial and error" calibration module. The determination of the N mineralization rate by inverse modelling with PEST using measured nitrate concentrations was not possible, and several reasons for this are given. With more suitable experimental fields (lighter soil texture and/or deeper groundwater level), more replications in the nitrate measurements and a one-step calibration of the alpha parameter and the N mineralization rate, determination of the N mineralization rate may become possible.