|Hook, J - UNIVERSITY OF GEORGIA|
|Gascho, G - UNIV. OF GA|
|Davis, J - COLORADO STATE UNIV.|
Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 18, 2003
Publication Date: June 20, 2004
Citation: Wauchope, R.D., Truman, C.C., Johnson, A.W., Sumner, H.R., Hook, J.E., Dowler, C.C., Chandler, L.D., Gascho, G.J., Davis, J.G. 2004. Fenamiphos losses under simulated rainfall: comparing plot scales. Transactions of the ASAE 47(3), 669-676(2004). Interpretive Summary: "Runoff" of pesticides--the loss of pesticides in water draining from the surfaces of fields under heavy rainfall -- is the most important route by which pesticides pollute streams and lakes. This is the first of a series of papers in which we will describe the pesticide runoff measurements we have made using a large-scale rainfall simulator. This equipment, built by Harold Sumner, allows us to "rain" on a 50' x 100' area whenever we wish. Because pesticide runoff is very sensitive to the timing of rainfall after a pesticide is applied (rain immediately after application gives the highest concentrations), this allows us to measure runoff under "worst-case" conditions. In this experiment we used fenamiphos, an important nematicide and also compared the mesoplot with much smaller "microplots", under the same rain simulator. We found that in this case the microplots would have worked just as well.
Technical Abstract: A large-scale (0.06ha) "mesoplot" rainfall simulator was used to apply 5cm of rain in 20 hours 1 day, 14 days and 28 days after application and incorporation of fenamiphos nematicide, simulating "reasonable worst case" runoff conditions. The mesoplots consisted of eight 43m corn beds parallel to the slope. Smaller "microplots", 1 bed x 10m in length were also placed under the simulator to compare the effects of scale. Total fenamiphos losses were about 1.5% of amounts applied with 4/5 of the loss in the first event after application. The majority of loss was in the sulfoxide form, which made up half the loss in the first event and nearly all the loss in later events. Runoff losses varied between years and plot groups but in general mesoplots and microplots gave similar results, suggesting that the latter may be adequate for measuring pesticide runoff for bare-soil water-carried solute conditions.