Title: Polyacrylamide effects on aggregate and structure stability of soils with different clay mineralogy Authors
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 5, 2010
Publication Date: July 1, 2010
Repository URL: http://naldc.nal.usda.gov/download/44417/PDF
Citation: Mamedov, A.I., Wagner, L.E., Huang, C., Norton, L.D., Levy, G.J. 2010. Polyacrylamide effects on aggregate and structure stability of soils with different clay mineralogy. Soil Science Society of America Journal. 74(5):1720-1732. Interpretive Summary: Environmentally friendly anionic polyacrylamide (PAM) is used to prevent runoff and erosion to help sustain soil quality and prevent surface water pollution. However PAM application studies have yielded conflicting results. Little research has been done on the degree of effectiveness on different soil types and application methods. We studied the effectiveness of PAM application on aggregate and structure stability for 16 soils collected from arid and humid zones. Soils having a loam or clay texture were evaluated having different clay mineralogy (i.e., smectitic (7 soils), illitic (5 soils), and kaolinitic (4 soils)). All these soils are widely distributed in the U.S. Soil aggregate structure stability was estimated from the sensitivity of aggregates to slaking. For the non-treated soils, their aggregate structure stability, hence a soil’s draining ability were in the order of smectitic < illitic soils < kaolinitic. Addition of PAM increased the soil moisture content of the aggregates at saturation, which increased their drainable pores, leading to an increase in the stability of the aggregates compared with the untreated ones. The aggregate and structure stability of the PAM treated soils were close to each other. Therefore, the effectiveness of PAM in improving aggregate stability in these soils followed in the order of smectitic > illitic> kaolinitic clay mineralogy. Thus, the weaker aggregates were more strongly affected by the addition of PAM. In conclusion, this study showed that the effectiveness of PAM for increasing aggregate stability depended on soil clay mineralogy (i.e. clay activity = cation exchange capacity/clay content) and to soil conditions affecting PAM adsorption (salts, pH and cations). These data are readily available from USDA-NRCS soil surveys and should be considered before the use of PAM to obtain maximal effectiveness from its use in arid and humid regions. Moreover additional experiments on effect of wetting-drying cycles, PAM concentration and cation composition on soil aggregates and structural stability will contribute to better utilization of PAM under field conditions.
Technical Abstract: Adding anionic polyacrylamide (PAM) to soils stabilizes existing aggregates and improves bonding between and aggregation of soil particles. However, the dependence of PAM efficacy as an aggregate stabilizing agent with soils having different clay mineralogy has not been studied. Sixteen soil samples (loam or clay) with predominantly smectitic, illitic, or kaolinitic clay mineralogy were studied. We measured aggregate sensitivity to slaking in soils that were untreated or treated with an anionic high-molecular-weight PAM using the high energy moisture characteristic (HEMC) method and deionized water. The index for aggregate susceptibility to slaking, termed stability ratio (SR), was obtained from quantifying differences in the water retention curves at a matric potential range of 0 to –5.0 J kg–1 for the treatments studied. For the untreated soils, the SR ranged widely from 0.24 to 0.80 and generally SR of kaolinitic > illitic > smectitic soils. The SR of PAM-treated aggregates exhibited a narrow range from 0.70 to 0.94. The efficiency of PAM in improving aggregate and structural stability relative to untreated soils ranged from 1.01 to 3.90 and the relative SR of kaolinitic < illitic < smectitic samples. These results suggest that the less stable the aggregates the greater the effectiveness of PAM in increasing aggregates stability (i.e., smectitic vs. kaolinitic samples). The effectiveness of PAM in improving structure and aggregate stability was directly related to clay activity and to soil conditions affecting PAM adsorption (e.g., electrolyte resources, pH, and exchangeable cations) to the soil particles and inversely to the inherent aggregate stability.