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  2000 Table of Contents

2000 STEEP III Progress Report

RESEARCH PROJECT TITLE: The influence of polyacrylamide on the movement of soil-applied herbicides in furrow-irrigated dry bean (Phaseolus vulgaris)


Don W. Morishita, Michael J. Wille, and Matthew J. West, University of Idaho and Robert E. Sojka, USDA-ARS Northwest Irrigation and Soils Research Laboratory



  1. Determine the effect of polyacrylamide (PAM) on the transport of two herbicide classes represented by ethalfluralin and dimethenamid from the field in the irrigation outflow and eroded soil sediments, using furrow-irrigated dry bean as a model crop.
  2. Determine the effect of PAM on the vertical and lateral movement of these herbicides in the soil.
  3. Evaluate crop injury by visual assessment and measuring fresh weight of aboveground biomass of the crop.
  4. Evaluate weed control efficacy by determining weed populations prior to the initial irrigation and 7 to 10 days after each subsequent irrigation.
  5. Determine the effect of PAM on weed seed migration from the field in irrigation water.

KEY WORDS: herbicide movement, ethalfluralin, dimethenamid


Irrigated agriculture has been identified as a major non-point source of water pollution. Over 7,904,000 acres are irrigated in the PNW with about 43% surface irrigated. Return flows from eroded fields to surface water may include soil sediment, nutrients, and pesticides. From 12 to 124 tons of soil per acre can be lost each year from typical surface irrigated fields in the PNW.

Using polyacrylamide (PAM) in surface irrigation can reduce soil erosion from furrow irrigated fields by 94% and increase infiltration by 15%. However, little is known how PAM may influence the movement of soil-applied herbicides. If this technology is to develop to its full potential, it is necessary to understand the influence that it may have on the movement of soil-applied herbicides both within the field and from the field.

ZONE OF INTEREST: Irrigated agriculture in the PNW


This project was initiated in May 2000. Funding will provide the salary of a graduate student and the cost of herbicide residue analysis of soil and water samples. Ethalfluralin and dimethenamid-P were applied and incorporated into the soil prior to planting dry bean. Water samples were collected from each irrigation event. Soil samples were taken at the top middle and bottom of the field and in the furrow, shoulder, and top of the row at each of the sampling locations. Soil samples were taken within 4 days after each irrigation and just prior to the first irrigation. Weed counts were taken in the same general area of the soil samples. Herbicide residue analysis of the water and soil samples is not yet completed. Weed densities were higher in the untreated control compared to the herbicide treatments, but PAM application did not affect weed densities. Dry bean biomass was lower in the untreated check averaging 147 g/m2 compared to the ethalfluralin and dimethenamid herbicide treatments, which averaged 382 and 380 g/m2, respectively. Averaged across weed control treatments, dry bean biomass in the PAM treatments averaged 359 g/m2 compared to the no-PAM treatments, which averaged 247 g/m2. Similar results were observed in dry bean yield. Dry bean yield of the untreated control was reduced 55% compared to the average yield of the herbicide treatments. However, dry bean yield was not affected by the PAM application. Processing of weed seed migration samples collected at each irrigation event have not yet been completed.


Results of the first year of this two-year study have not been compiled.


none at this time.


none at this time.


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