1989 - 1994
Transport And Dissipation Pathways Of Pesticides In
G.J. Wall1, B.T. Bowman2,
B.A. Grant3 and D.J. King1
Download Report (150 KB pdf)
The detection of pesticides in surface waters has caused great concern about human and ecosystem health. Concentrations often exceeding water quality guidelines are frequently detected in surface water throughout the growing season, with the highest concentrations being observed in May and June (Thurman et al. 1992, Isensee, A. R. et al. 1990).
Agricultural pesticides make up the largest percentage of pesticides used in the Great Lakes Basin (Mokley, J. 1989). Significant amounts of pesticides, mostly herbicides are used annually to increase crop yield. As a result of the large amount of pesticides used, they are commonly found in the tributaries of the Great Lakes, but little was known about the transport pathways and processes of herbicides from the point of application in the farmer's field to the point of deposition into the Great Lakes (Buttle, J. M. 1989).
Movement of pesticides from agricultural lands is a complicated process. It depends on several factors including the characteristics of the pesticide (solubility, decay constant etc), and the amount of water travelling through and off the soil from the time the pesticide is applied until degradation (Bowman et al., 1994). Other important associated factors are soil type, soil moisture and soil hydrological properties. The greater the soils ability to hold water the less runoff and percolation will occur resulting in the pesticide remaining in the soil profile for microbial degradation.
Microbial degradation tends to be the most important breakdown route for many soil-applied herbicides, as compared to chemical breakdown processes. Of the factors which influence microbial activity in soil, both moisture and temperature rank amongst the most important. Previous research has demonstrated that tillage practices influence temperature and moisture regimes in soil (Kovar et al., 1992). It is a well-established fact that no-till soils appear to be wetter at planting time than conventionally-tilled soils, perhaps because soil cultivation accelerates surface moisture losses, which in turn might also permit those soils to warm up more quickly.
The increase in conservation tillage in the 1980's raised the concern of the potential increase in pesticide use, and the corresponding potential increase of pesticide loss. It was believed that the trend toward less tillage would result in greater weed problems, therefore resulting in a need to increase herbicide usage. This could result in an increase in pesticide loss to surface water. Other perceptions accompanying the increased use of conservation tillage systems were that increased residue would decrease runoff, thereby reducing pesticide loss by surface flow, but possibly increasing pesticide loss through preferential flow (Hinkle, M.K. 1983).
New technologies and better understandings of pesticide movement were required to move to sustainable productions systems. Non-point-source (NPS) models were thought to be a possible tool in educating farmers about pesticide loss and remedial actions which could reduce the environmental impacts of pesticide movement. Field based models such as CREAMS, GLEAMS and DRAINMOD could be used to show the effects of tillage and application timing on pesticide loss. These models have the ability to simulate the movement of sediment, nutrients and pesticides to surface water, tile water and groundwater (Knisel 1980). Several of the models have been modified and combined to give a complete simulation of the movement of pesticides and nutrients from surface runoff to groundwater. The major problem with the models was the lack of applicable data to calibrate these field scale models for Ontario conditions. It was thought that once the models were calibrated, they would be a useful tool in Environmental Farm Planning.
The objectives of this study were:
HERBICIDE TRANSPORT STUDY
NEW TECHNOLOGIES AND BENEFITS
The development of pan lysimeters allows the ability to do a mass water balance and determine the effects of tillage on soil hydrological properties and contaminant transport. They also provide the ability to get a better understanding of the seasonal changes in soil hydrological properties. They provide a relatively low cost screening method to study various pesticides and cropping practices, allowing research to focus on agricultural practices that pose a potential threat to water quality.
The availability of automated temperature and moisture (multiplexed TDR) systems now make it possible to accurately track moisture and temperature fluxes in soil profiles. This permits a more precise description of the micro-environment which greatly influences the disposition of applied agrochemicals. Multiplexed, automated TDR systems became available only within that past two years.
The data which was collected over the five year study will be useful for calibrating and evaluating computer models for Environmental Farm Planning. Once the models have been calibrated they can be used to demonstrate the effects of management practices on pesticide movement. They will be valuable tools in showing the farmers the benefits of old techniques such as banding herbicide applications to reduce herbicide and soil loss through conservation tillage.
IMPLICATIONS FOR GREAT LAKES BASIN ECOSYSTEM
Pesticide transport form agricultural land is a wide spread problem in the Great Lakes Basin. Up to this point the true pathways and processes of pesticide movement from agricultural lands were not clearly understood. As we move toward more sustainable farming systems, it is imperative that we more fully understand the cropping systems we use. This study has made some important observations regarding some of the changes which take place as a conventionally-tilled system is converted to a no-tillage practice. In order to fully appreciate the impact of these changes, it is necessary to monitor some of the important parameters controlling crop growth and performance, such as soil temperature and moisture. A better understanding of the micro-ecosystem will be an aid in optimizing inputs, and in reducing nutrient and pesticide inputs to the Great Lakes system.
With the information and data collected from this studied researchers will be better able to predict possible areas of concern. Using provincial databases scientist will be able to determine susceptible areas of pesticide movement based on soil type, crop distribution, pesticide use and tile drain information. These areas can than be targeted for educational and incentive programs to increase farmer awareness and decrease the potential pesticide loss. Models calibrated from the data can be used to show the effects of management practices on pesticide movement form agricultural lands.
The study has shown that pesticide movement may be a wide spread problem from both surface runoff and tile flow. It has shown that surface runoff and tile flow are significant pathways for pesticides reaching the Great Lakes ecosystem.
Even though banded applications of herbicides is an old practices, it is not a wide spread practice. The results of this study should be used to increase the awareness and the benefits of banded application of herbicides on conventional and minimum tilled sites.
The highest potential for pesticide loss occurs shortly after herbicide application. This information has to be transferred to the farmers so that they will be better able to decrease herbicide loss through proper timing of application (not prior to a predicted rainfall).
GAPS NEEDING FUTURE RESEARCH
Thursday, May 05, 2011 09:53:26 PM