Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 23, 1997
Publication Date: N/A
Interpretive Summary: There is a growing concern about the contamination of surface water bodies. Increasing use of pesticides in current agricultural production has significantly improved crop productivity, but it has also adversely affected environmental quality. Pesticide loss in water runoff not only deteriorates surface water quality but also increases the potential for groundwater pollution. This study was conducted to evaluate the effects of rainfall pattern/distribution and antecedent soil water content on herbicide loss in surface water runoff. The results showed that application of herbicides to wet soil surface tended to cause greater herbicide loss in water runoff as compared to application of herbicides to dry soil surface. Rainfall storms with heavy rain falling in the early stages of the storms caused much more herbicide loss in water runoff than the storms with heavy rain falling in the late stages. The results also indicated that herbicide loss in water runoff could be well predicted with the mathematical model proposed in this paper. This study provided some useful information to environment conservationists and farmers on how to reduce herbicide loss in water runoff. The results were also useful for researchers to develop a solid predictive tool, which can be used to select the environment sound agricultural management practices.
Technical Abstract: Since herbicide concentration in runoff varies dramatically within a single storm, storm pattern is postulated to have a significant impact on herbicide loss. This study was to evaluate the effects of storm pattern and moisture content on herbicide runoff and to validate the uniform mixing concept for modeling herbicide transfer to runoff. Atrazine and metolachlor were sprayed onto the dry soil surface at the rates of 1.12 and 2.24 kg/ha, respectively. A complete combination of two soils (Cecil sandy loam and Miami silty loam), four storm patterns (uniform, advanced peak, intermediate peak, and delayed peak), and two moisture levels (wet and dry) was conducted in duplicate. Dissolved herbicide runoff from the advanced peak was twice as much as those from the other rains for both herbicides for the Cecil soil. Although the significance was reduced for the Miami soil, the metolachlor loss from the advanced peak was still greater than from the delayed peak. Rain pattern also affected adsorbed herbicide loss, but no consistent trend was shown for both soils. Wet treatment showed higher dissolved and adsorbed herbicide concentrations in runoff for both herbicides on the Miami soil and for metolachlor on the Cecil soil, indicating the greater potential for herbicide loss under wet conditions. Herbicide concentrations decreased exponentially with cumulative rainfall depth, irrespective of rain patterns, indicating the uniform mixing model matched the data well. Results show that information on rain distribution and transient infiltration rate are needed for better predicting both instantaneous and total herbicide losses during a single storm.