Development and validation of the SPEC model for simulating the fate and transport of pesticide applied to Japanese upland agricultural soil

: A pesticide fate and transport model, SPEC, was developed for assessing Soil-PEC (Predicted Environmental Concentrations in agricultural soils) for pesticide residues in upland field environments. The SPEC model was validated for predicting the water content and concentrations of atrazine and metolachlor in 5-cm deep soil. Uncertainty and sensitivity analyses were used to evaluate the robustness of the model's predictions. The predicted daily soil water contents were accurate regarding the number of observation points (n=269). The coefficient of determination (R2) and Nash-Sutcliffe efficiency (NSE ) were equal to 0.38 and 0.22, respectively. The predicted daily concentrations of atrazine and metolachlor were also satisfactory since the R2 and NSE statistics were greater than 0.91 and 0.76, respectively. The field capacity, the saturated water content of the soil and the Q10 parameter were identified as major contributors to variation in predicted soil water content or/and herbicide concentrations.