Submitted to: Soil and Water Conservation Society
Publication Type: Abstract Only
Publication Acceptance Date: December 20, 2002
Publication Date: December 31, 2002
Citation: STOTT, D.E., GREEN, V.S., FANTA, G.F. PAM FORMULATIONS: EFFECTS ON EFFICACY. SOIL AND WATER CONSERVATION SOCIETY MEETING. 2002. 57:304. Interpretive Summary: Eroded sediments remain the leading pollutant of surface waters, causing the displacement of nutrients and pesticides from the soil surface to lakes, rivers, and streams. In western regions of the U.S., the use of polyacrylamide (PAM) to control erosion in furrow irrigation systems has increased dramatically. PAM is placed in the furrow either as a solid before the start of water flow or as a liquid in the first irrigation water added to the furrow. PAM flocculates the surface particles, stabilizing soil aggregates against the flowing water, and preventing the formation of a surface crust and subsequent rill erosion. This process reduces sediment detachment and flow, and increases water infiltration. This, in turn, conserves both soil and water. Additional advantages include a more even wetting of the field leading to increased yields, reduction in the number of times the furrow needs to be reformed during a growing season, and retention of plant nutrients on the field. PAM is actually a class of polymers that vary in size, molecular weight, and charge density. These variations cause differences in performance as a soil flocculant in furrow irrigation systems. Until now, only three or four types of molecular configurations of PAM have been tested for the ability to reduce rill erosion. We studied the effect of changing the charge density of anionic PAMs on reducing sediment loss. A PAM with a molecular weight of about five to six million grams per mole was used. In commercial PAM formulations, this is referred to as a high molecular weight PAM. This study was done in a laboratory using a mini-rill flume, which simulates the furrow. The results from previous mini-rill flume studies have correlated well with field furrow irrigation studies. We found that a charge density, measured as the rate of hydrolysis of the parent PAM molecule, between 25 and 35% was the most effective in stopping rill erosion. The impact is that this work can be used as a guideline for choosing the most effective PAM amongst the PAM products that are currently approved for use in furrow irrigation.
Technical Abstract: Polyacrylamides (PAM) are being used to stabilize the soil surface against crusting and erosion. The practice is becoming wide spread in the furrow irrigation systems in the Western States. At this time, only a few of the many commercially available PAM formulations have been tested for use as a soil stabilizer. A study was designed to determine how changes in polymer charge density and application concentration altered the effectiveness of PAM to reduce surface sealing and thereby controlling sediment loss. Mini-rill flumes were used to examine the effectiveness of the polymers. Alteration of polymer charge densities was achieved through carboxylation of a parent polymer that had a molecular weight range of 5 to 6 Mg mol-1 (5 to 6 million daltons). Maximum control of rill erosion was achieved when 25 to 30% of the PAM amide side groups were replaced by carboxyl groups. Within that percent hydrolysis range, soil amended with a 0.3 ppm solution applied to the surface could withstand stream power forces up to 6.5×10-4 Pa m s-1. Soil surfaces amended with a 0.5 ppm solution withstood stream power forces up to 3.1×10-4 Pa m s-1.