Sensitivity analysis of CSM-CERES-MAIZE
to field capacity for simulating nitrogen fate in soil profile

Field capacity (FC) is one of the important parameters of soil-water-crop-atmosphere models which the accurate measurement of this parameter is very expensive and time consuming. In this study the sensitivity of the CSM-CERES-Maize model to FC for simulating soil nitrate and ammonium concentration in different soil layers، and plant N uptake was evaluated. The study was performed using the experimental data obtained from the field study conducted on silage maize in 2003 and 2004 at south Tehran، Iran. The treatments were consisted of four irrigation levels (0. 7، 0. 85، 1 and 1. 13 soil moisture depletion) with three fertilizer levels (0، 150، and 200 kg N ha-1). The results indicated that the change of simulated soil nitrate concentration was between 7. 17 and 96. 75 due to 25% changes in FC (either increase or decrease). This value for simulated soil ammonium concentration was between 33. 31 and 139. 01. The CERES model was sensitive to FC changes in simulation of soil nitrate and ammonium concentrations and its sensitivity was different in soil layers. This model was less sensitive to FC changes in simulating mineralization، nitrification، and plant N concentration. It can be then calculated that an exact determination of FC can reduce uncertainty in simulating soil nitrate and ammonium concentrations using the CERES model.