Behaviour of herbicides in soil : simulation and experimental assessment

The mathematical models of the transport and the transformation rate of herbicides in soil that are available in the literature and the tests done on them are reviewed.A simulation model of the transport of herbicides in field soil, based on the best model available in the literature, was developed. The detailed field experiments carried out on a bare loamy sand soil with two soil-applied herbicides (cyanazine and metribuzin) in spring and summer to test this model are described.A new sub-model for the evaporation of water from bare soil was developed and tested in the field, with acceptable results. Testing the herbicide transport model against the concentration profiles measured in the field, showed that calculated penetration of the two herbicides in soil at a few months after application was much deeper than that measured.To elucidate the cause of the discrepancy between calculations and measurements, the sorption of the two herbicides onto soil collected from the experimental field was studied in detail in laboratory experiments. Based on these studies a new model for the sorption of the herbicides was developed and incorporated into the transport model. The main new element in this model was a sorption process that equilibrates at a time scale of months. A comparison between concentration profiles calculated with the new model and those measured in the field showed that the new model successfully explained the field measurements

Spatial moment analysis of transport of nonlinearly absorbing pesticides using analytical approximations

Analytical approximations were derived for solute transport of pesticides subject to Freundlich sorption, and first-order degradation restricted to the liquid phase. Solute transport was based on the convection-dispersion equation (CDE) assuming steady flow. The center of mass (first spatial moment) was approximated both for a non-degraded solute pulse and for a pulse degraded in the liquid phase. The remaining mass (zeroth spatial moment) of a linearly sorbing solute degraded in the liquid phase was found to be a function of only the center of mass (first spatial moment) and the Damköhler number (i.e., the product of degradation rate coefficient and dispersivity divided by flow velocity). This relationship between the zeroth and first spatial moments was shown to apply to nonlinearly sorbing pulses as well. The mass fraction leached of a pesticide subject to Freundlich sorption and first-order degradation in the solution phase only was found to be a function of the Damköhler number and of the dispersivity, so independent of sorption. Hence perceptions of the effects of sorption on pesticide leaching should be reconsidered. These conclusions equally hold for other micropollutants that degrade in the solution phase onl

Emissies van bestrijdingsmiddelen bij het spoelen van bloembollen

De emissies van bestrijdingsmiddelen naar grondwater en via af te voeren spoelslib uit de bloembollenteelt is geschat met eenvoudige modellen. In spoelslib zullen vooral middelen worden aangetroffen die sterk adsorberen aan organische stof of in hoge dosering worden toegepast, zoals tolclofosmethyl en prochloraz. De gemeten verzadigde doorlatendheid van bassinbodems bedroeg 0,2 tot 0,5 cm/d, wat resulteerde in berekende waterfluxen door de bassinbodem van 4 tot 5 cm/d. Bij zulke hoge fluxen zal de concentratie van carbendazim maar weinig dalen tijdens het transport vanuit bassins naar het grondwate

Manual of PEARLNEQ v5

This manual describes the PEARLNEQ v5 software package . This package can estimate long-term sorption parameters using results of aged-sorption studies with soil, using a submodel for sorption and transformation that is identical to the submodel used for that purpose in the FOCUS_PEARL v3.3.3. The submodel assumes two types of sorption sites: equilibrium sites and non-equilibrium sites. The sorption isotherms for both sites are described with Freundlich equations. The mathematical equations describing the submodel are solved via a FORTRAN programme. An additional FORTRAN programme generates the necessary input files for the PEST optimisation package. Instructions are given how to obtain optimized parameters using an example dataset and how to obtain parameters using your own data

PEARL model for pesticide behaviour and emissions in soil-plant systems : description of the processes in FOCUS PEARL v 1.1.1

The use of pesticides in agriculture presents risks to the environment, which are increasingly evaluated by using computation models. The new PEARL model simulates the behaviour of pesticides in soil-plant systems and their emissions to the environment. The pesticide model is used in combination with the hydrological model SWAP. Various agricultural situations and ways of applying the pesticides can be simulated. The model accounts for different sorption mechanisms, in equilibrium and non-equilibriumdomains of the soil. Pesticide transport in the liquid and gas phases is described by the convection-dispersion-diffusion type equation, which is supplemented with sink terms. Comprehensive reaction schemes are processed in matrix form. The rate in first-order transformation kinetics is dependent on temperature, soil moisture content and depth in the soil. Besides computing persistence and distribution of the pesticidal compounds in soil, the model computes volatilization into the air, lateral drainage to water courses and leaching to groundwater

Manual of PEARLNEQ v4

This document describes a PEARLNEQ-PEST combination, which can be used to estimate the parameters for long-term sorption kinetics in the PEARL model on the basis of an incubation experiment for a certain soil and a certain pesticide. The combination provides also the transformation half-life at reference temperature (when long-term sorption kinetics are included in PEARL, the definition of this half-life changes so it has to be recalculate