A STELLA model for the estimation of atrazine runoff, leaching, adsorption, and degradation from an agricultural land

Abstract

Background, aim, and scope

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) is one of the most widely used herbicides for broadleaf weed and certain annual grass controls and is popular because of its effectiveness and low cost. Losses of atrazine from agricultural lands into adjacent surface water and underlying groundwater have raised public concerns. Several computer models have been developed for atrazine runoff in watersheds. One limitation for most of these models, however, is that vast amounts of input parameters are required for simulations. These input parameters are sometimes difficult to obtain through the experimental measurements for model calibrations, validations, and applications. Therefore, a need exists to develop a simple and yet a realistic modeling tool that can be used for effectively investigating atrazine dynamics in agricultural soils. This study was designed to meet this need.

Materials and methods

A model was developed based on atrazine dynamics in agricultural soils. These dynamics include atrazine (1) application to soil, (2) loss from surface runoff, (3) volatilization, (4) sorption, (5) degradation, (6) root uptake, and (7) leaching. The model was constructed using the commercially available package Structural Thinking, Experiential Learning Laboratory with Animation (STELLA) and calibrated using field data prior to its applications.

Results and discussion

A simulation scenario was then performed to predict atrazine fate in a 1-ha field. Simulation results showed that atrazine runoff and leaching occurred within the first coupled rainfall events with a duration of about 40 days after its application to the soil. This occurred because atrazine was strongly adsorbed by the soil in addition to its degradation by soil microorganisms, volatilization to the atmosphere, and uptake by roots. The maximum adsorption rate of atrazine was found in 1 day and reached an equilibrium condition in about 100 days. Two degradation phases, namely, the fast and slow phases, were observed in this simulation. The fast degradation phase occurred within 1 week after atrazine application, whereas the slow degradation phase took place after 1 week of the atrazine application. About 25% of the total applied atrazine still remained in the soil at the end of the simulation period (120 days). Of which, almost all of them were retained in the solid phase.

Conclusions

A very good agreement was obtained between the model predictions and the field measurements. The model was quite successfully applied to predict the complex behaviors of atrazine in the soil.

Recommendations and perspectives

This study suggests that the model, developed with STELLA, has great potentials as a modeling tool for effective investigations of atrazine dynamics in agricultural soils due to its being simple and yet realistic.