Two methods were used to obtain the sensitivity of chemical leaching depth to variations in the input parameters of the Pesticide Root Zone Model (PRZM). First a Plackett-Burman (PB) screening design was used to vary 35 PRZM inputs over seven ranges around a nominal value. Six of the seven ranges were approximately 0.1, 0.25, 0.5, 1.0, 5.0, and 15%, the seventh range was chosen to cover a range appropriate for a soybean herbicide applied preemergence in the Midwestern region defined by the USDA–SCS land resource region M. Next, Fourier amplitude sensitivity testing (FAST) was then used to vary from 19 to 25 parameters over four of the ranges previously tested. For the smaller parameter ranges the two methods typically gave equivalent results but the PB method required far fewer simulations. For the simulation of the Midwestern region where some parameter varied by larger amounts the relative magnitudes of the sensitivity coefficients obtained by the two methods were similar but the magnitude of the coefficients obtained using FAST were smaller than those obtained using PB.
