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E. Perfect and B. D. Kay

Anionic polyacrylamide (PAM) may be economical as a soil conditioner (SC) if it can stabilize structure at low application rates. Information addressing the influence of PAM on stability with low application rates and comparing improvements in stability measured under moist and air‐dry conditions is lacking. We studied the influence of two PAM SC (2J and 21J), each applied at three rates (25, 50, and 75 mg kg‐1), on the wet and dry aggregate stabilities of a Gilat sandy loam soil (typic Haplargid), leached with either Ca or Na salts. The resulting changes in bulk density (BD) and saturated hydraulic conductivity were also measured. Dry aggregate stability was characterized by the Weibull parameters, α and β, where α is the specific rupture energy and β describes the spread in rupture energies. Wet‐aggregate stability was characterized by the drop test (Dt) and the mass fraction of stable aggregates after wet sieving. The increase in α produced by 2J was greater than that produced by 21J. The α was higher for the Na‐leached aggregates than for the Ca‐leached ones. The log(α) was correlated with BD (r = 0.93). The PAM application increased the spread in rupture energies for the Ca‐saturated aggregates and decreased the spread for the Na‐saturated aggregates. The Dt was correlated with log(α) (r = 0.53), indicating increased stability in the air‐dry state was associated with increased stability under moist conditions. Improvements in stability achieved at low PAM application rates depend upon polymer charge density, soil moisture content, and type of exchangeable ion.

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Effect of Polyacrylamide Application on the Stability of Dry and Wet Aggregates
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E. Perfect and B. D. Kay

Effect of Polyacrylamide Application on the Stability of Dry and Wet Aggregates

Anionic polyacrylamide (PAM) may be economical as a soil conditioner (SC) if it can stabilize structure at low application rates. Information addressing the influence of PAM on stability with low application rates and comparing improvements in stability measured under moist and air‐dry conditions is lacking. We studied the influence of two PAM SC (2J and 21J), each applied at three rates (25, 50, and 75 mg kg‐1), on the wet and dry aggregate stabilities of a Gilat sandy loam soil (typic Haplargid), leached with either Ca or Na salts. The resulting changes in bulk density (BD) and saturated hydraulic conductivity were also measured. Dry aggregate stability was characterized by the Weibull parameters, α and β, where α is the specific rupture energy and β describes the spread in rupture energies. Wet‐aggregate stability was characterized by the drop test (Dt) and the mass fraction of stable aggregates after wet sieving. The increase in α produced by 2J was greater than that produced by 21J. The α was higher for the Na‐leached aggregates than for the Ca‐leached ones. The log(α) was correlated with BD (r = 0.93). The PAM application increased the spread in rupture energies for the Ca‐saturated aggregates and decreased the spread for the Na‐saturated aggregates. The Dt was correlated with log(α) (r = 0.53), indicating increased stability in the air‐dry state was associated with increased stability under moist conditions. Improvements in stability achieved at low PAM application rates depend upon polymer charge density, soil moisture content, and type of exchangeable ion.

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