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Fate and Efficacy of Polyacrylamide Applied in Furrow Imgation: Full-Advance and Continuous Tr... <br />Page 13 of 16 <br />When the >6 mg L-I PAM a.i. application ceased, PAM concentration in furrow runoff declined rapidly. However, <br />while dissolved PAM was being added to furrow irrigation streams, its downstream persistence in the flow was a <br />function of its initial concentration and irrigation sequence. Results were consistent with the concept that furrow <br />sediment concentration is an important factor controlling the downstream dissolved PAM concentrations in furrow <br />and tail-ditch streams. When furrow inflows contained >6 mg L-I PAM a.i., the polymer persisted in downstream <br />flows because at these application rates, PAM greatly minimized entrained sediment concentrations and hence PAM <br />adsorption. Increasing sediment concentrations in treated furrow or tail-ditch flows, either by decreasing PAM a.i. <br />application rate to concentrations below 0.9 mg L-I or by adding sediment via tributary inflows, promoted the <br />removal of dissolved PAM in downstream flows. Other less-understood factors also appear to influence dissolved <br />PAM concentrations in treated flows. While some results were unexplained, we found no consistent evidence that <br />PAM desorbed from treated furrow soils. However, further study is needed to fully understand the importance of all <br />processes that influence furrow stream PAM concentrations. <br />To maximize PAM-use efficacy and minimize its transport off-site, imgators need to keep applied polymer in the <br />field. This is best achieved by ceasing >6 mg L' I PAM a.i. applications before or immediately after furrow advance <br />occurs, and refraining from treating late-season irrigations. However, even if PAM applications were continued after <br />advance, our results indicate that dissolved PAM concentrations decline quickly after PAM-treated flows join <br />untreated streams. While Initial-10 PAM treatment continued for 1.2 to 2 h after advance in this study, only 1% of the <br />applied PAM was transported to the end of the 530-m tail ditch. Tail-water ditches used on many farms in the area are <br />two to three times longer than that used in this study. Under these conditions, and even if the PAM application were <br />continued after advance, it appeazs unlikely that significant quantities of dissolved PAM could persist in tail ditch and <br />irrigation return flows long enough to enter natural waterways. <br />- ACKNOWLEDGMENTS <br />This work was supported in part by a grant from CYTEC Industries, through a Cooperative Research and <br />Development Agreement (contract 58-3K95-4-216). We thank Dr. Craig Ross, Mr. Ron Peckenpaugh, Mr. Jim <br />Foerster, and Ms. Barbara Prater for their valuable technical assistance, and Ms. M. Emily Aston, Ms. Elizabeth <br />Whitchurch, and Mr. Paul Miller for their help in the lab and field. <br />- NOTES <br />Mention of trademark, proprietary products, or vendors does not constitute a <br />guarantee or warranty of the product by the USDA-ARS and does not imply its <br />approval to the exclusion of other products or vendors that may also be available. <br />0 <br />- REFERENCES <br />Agassi, M., J. Letey, W.J. Farmer, and P. Clark. 1995. Soil erosion <br />contribution to pesticide transport by furrow irrigation. J. Environ. Qual. <br />24:892-895.jISIj <br />~ TOP <br />~ ABSTRACT <br />~ INTRODUCTION <br />MATERIALS AND METHODS <br />• NOTES <br />~ RESULTS AND DISCUSSION <br />~ CONCLUSIONS <br />~ REFERENCES <br />TOP <br />ABSTRACT <br />~ INTRODUCTION <br />~ MATERIALS AND METHODS <br />~ NOTES <br />http://jeq.scijournals.org/cgi/content/full/31/2/661 9/21/2006 <br />