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

Abstract

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 (R 2 ) and Nash-Sutcliffe efficiency (N SE ) were equal to 0.38 and 0.22, respectively. The predicted daily concentrations of atrazine and metolachlor were also satisfactory since the R 2 and N SE statistics were greater than 0.91 and 0.76, respectively. The field capacity, the saturated water content of the soil and the Q 10 parameter were identified as major contributors to variation in predicted soil water content or/and herbicide concentrations.

Modeling of runoff water and runoff pesticide concentrations in upland bare soil using improved SPEC model

“…The relationship of S (in mm) to the runoff curve number CN (CN is a transformation of S) was defined in the previous study. 8) The details for updating S were also defined in Boulange et al 8) In every time step, the water content in every soil layer is updated as a function of input water from infiltration or percolation from right above the layer and evaporation from that soil layer. The evaporation from the soil layer is determined using the method specified in Neitsch et al (2011).…”

“…38) Pesticide parameters such as the first order rate coefficients of photodegradation and biodegradation were determined in the previous study. 8) The pesticide masses in each layer were determined in a manner similar to that in Boulange et al 8) In this study, two new terms were added to the pesticide calculation: the ratio of pesticide concentrations in mobile water and static water, α; and the ratio of pesticide concentrations in runoff water and percolation water, β. The α and β parameters account for the differences in pesticide concentrations in soil water, percolation water, and runoff water.…”

“…[3][4][5] In recent years, water quality models have been widely used as supporting tools for Environmental Impact Assessment (EIA). 6) In Japan, many mathematical models were developed to simulate pesticides in catchment as well as plot scales for paddy fields, 3,[7][8][9][10][11][12] but very few models were developed to apply in upland fields. 8) SPEC, a pesticide fate and transport model for assessing Soil-PEC (Predicted Environmental Concentrations in agricultural soils), was developed to simulate pesticides in upland fields and has been successfully validated.…”

“…6) In Japan, many mathematical models were developed to simulate pesticides in catchment as well as plot scales for paddy fields, 3,[7][8][9][10][11][12] but very few models were developed to apply in upland fields. 8) SPEC, a pesticide fate and transport model for assessing Soil-PEC (Predicted Environmental Concentrations in agricultural soils), was developed to simulate pesticides in upland fields and has been successfully validated. 8) This model requires fewer input parameters, overcoming the difficulty of obtaining sufficient parameters when using other mathematic models.…”

“…8) SPEC, a pesticide fate and transport model for assessing Soil-PEC (Predicted Environmental Concentrations in agricultural soils), was developed to simulate pesticides in upland fields and has been successfully validated. 8) This model requires fewer input parameters, overcoming the difficulty of obtaining sufficient parameters when using other mathematic models. In addition, because it was coded in Excel Visual Basic Application (Excel VBA), it is easy to use in terms of data input and output display.…”