Polymer effects on surface mechanical strength of a crusting loessial soil

Abstract

Addition of synthetic polymers to crusting soils generally improves seedling emergence and this is thought to be caused by lower mechanical strength of the crusted soil surfaces. The objective of the present study was to evaluate the mechanism by which polymer addition contributes to the reduction in crust mechanical strength. Three polymers were used, 2 anionic polyacrylamides differing in their molecular weight, and a cationic polysaccharide. Samples of a silty loam calcareous loess (Calcic Haploxeralf) were packed to a depth of 78 mm in round pots having an internal diameter of 120 mm at the top. Polymer was added to the soil surface, at a rate of 20 or 40 kg/ha, by spraying a concentrated polymer solution. The pots were then exposed to 40 mm of simulated rainfall comprising either distilled water or tap water (electrical conductivity 0·97 dS/m). In an additional study, polymer was added to the tap water to form a dilute (20 or 40 g/m3) polymer solution which was then used in the 40-mm rain event. After the exposure to rain, the pots were transferred to a temperature-controlled room (30°C). Weight of the pots, moisture content of the upper 10 mm of the soil, and crust strength (impedance) determined with a 3·24-mm diameter probe were measured periodically up to 95% water loss in the soil. In most of the polymer treatments, moisture content immediately after the rain was in the range of 32–39%, which was significantly higher than that in the control (27–29%). In general, for a given moisture content, crust strength did not differ significantly between the control and the polymer treatments. However, moisture content for a given cumulative drying time was higher in the polymer treatments than in the control, indicating that polymer application delayed crust drying and maintained a crust with a lower mechanical strength for a longer period of time. Polyacrylamide with a low molecular weight, applied at a rate of 40 kg/ha, emerged as the most effective treatment for maintaining high moisture content in the upper soil layer, and hence a crust with a low mechanical strength.

Rainfall-Induced Soil Surface Sealing: A Critical Review of Observations, Conceptual Models, and Solutions

“…The the soil beneath. Variations and extensions of this basic observed thin seals in fact represent much thicker disturbed layers, where the unobserved remaining disapproach were suggested in a series of studies on infiltraturbed part can still affect the hydraulic properties of tion through sealed soils with constant seal properties the initial soil and, consequently, the flow processes in (Ahuja, 1974(Ahuja, , 1983Moore, 1981a;Parlange et al, 1984). the upper soil layer.…”

“…The maximal value measured by Eigel and applied in a series of studies dealing with infiltration Moore (1983) was 1.85 g cm Ϫ3 . Roth (1997) measured into sealed soils (Ahuja, 1983; Brakensiek and Rawls, maximal values of 1.78 to 1.91 g cm Ϫ3 for soils with silty sand, loamy sand, or sandy loam textures and values of 1983;Parlange et al, 1984;Vandevaere et al, 1998). Mualem and Assouline (1989) introduced a new con-1.44 to 1.65 g cm Ϫ3 for loess soils.…”

“…However, the agreement between the calcu-These treatments can address physical soil properties, lated and the observed infiltration rates indicates that the model is rather sensitive to the soil shear strength like the initial water content of the soil surface (Le Bissonnais and Singer, 1992), or the chemical conditions and accounts for it reasonably and in the right direction. The combination between the ESP of the soil, or the of the soil water system (Shainberg, 1992;Levy and Rapp, 1998). sodium adsorption ratio (SAR) of the soil solution, and EC of the applied water affects also greatly the soil The effect of the initial water content on seal formation is expressed through the relationships between stability and (Yong and Warkentin, 1966;Benjamin and Cruse, 1985).…”

Polyacrylamide in Agriculture and Environmental Land Management

“…In Australia, water-soluble PAMs are being marketed for use in center pivots on coarse sands as a water and nutrient conservation tool. Levy and Rapp (1999) reported that water-soluble PAM, applied to the surface of a silt loam soil, reduced the loss of water during the drying process.…”

Rainfall‐Induced Soil Surface Sealing: A Critical Review of Observations, Conceptual Models, and Solutions

“…Therefore, it is possible to evaluate the sensitivity of the modeled infiltration to changes in τ resulting from treatments that affect soil stability. These treatments can address physical soil properties, like the initial water content of the soil surface (Le Bissonnais and Singer, 1992), or the chemical conditions of the soil water system (Shainberg, 1992; Levy and Rapp, 1998).…”