Programme de bourses "Echanges Universitaires"

Assessing the effects of meteorological conditions on drift from pesticide application in a tropical mountainous region in Colombia

Master Thesis in Environmental Sciences ETH
Dominik Scheiben

In the mountainous regions of Colombia, agriculture is the most important source of income for the major part of the population. The farmers are forced to maximize their productivity by the application of pesticides. Besides the benefits of pesticides, there are crucial drawbacks such as environmental problems and human health risks. A problem in the use of pesticides is the pesticide drift, which is the amount of applied pesticide that does not reach the target, i.e. the crop, but goes directly into the soil, the water, the air or onto the applicators. Pesticide drift depends on factors like application method, type of spray equipment, meteorological conditions or stage of growth of the crops.
The aim of this master thesis is to assess the influence of the meteorological conditions on the pesticide drift in a mountainous region in Tunja, the province capital of Boyaca, Colombia. The focus of this thesis is the pesticide drift in and around potato fields.
From September until November 2008, we did spray simulation experiments with the fluorescent tracer Uranine. We used water-sensitive papers as droplet collectors and we determined the spray droplet dispersion with two different methods. The weight method consisted in weighting the water-sensitive papers before and after the spray simulations and calculate the amount of droplets absorbed by each paper with the weight difference. The tracer method consisted in analyzing the amount of Uranine on the papers after the spray simulation and calculate the amount of spray droplets by the amount of Uranine. A weather station recorded the meteorological conditions during the spray simulations.
The pesticide drift inside of the field depends mostly on the ground cover of the potato leafs. The pesticide drift with an average ground cover of 50% was measured to be about 83% of the applied dose. Outside of the field, the relative pesticide drift decreases exponentially with the distance to the field border parallel to the wind direction. A strong influence of the wind speed on drift outside the field was detected. As expected, the pesticide drift increases with increasing wind speed. Drift droplets were detected at the maximum measurement distance, at 20 meters. Pesticide drift onto the applicators was as high as 0.76% of the total applied liquid volume.
A pesticide drift prediction equation for the conditions in the study area is presented and existing drift prediction equations from other studies were compared and eventually adapted to the data from this study.
In addition to the droplet dispersion experiments, we did other spray simulations with Uranine in two catchment areas in the study area to determine the subterranean flow of the sprayed solution. The Uranine concentration in the water flows was measured, but we could only detect concentrations at the detection limit (< 0.1 μg/l). This indicates that a large fraction of the applied dose is retained by the soil.

The results from this master thesis can be used to model pesticide drift for different scenarios in the study area and imply actual pesticide concentrations to determine areas under the risk of contamination. Also, buffer zones could be proposed based on the results from this thesis.

Contact:
Switzerland:

Dominik Scheiben
Environmental Sciences
ETH Zürich
dominiks@student.ethz.ch

Colombia:

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