The effects of polyacrylamide on the parameters of physical quality in a clay loam soil selected from semiarid region

In semiarid regions, physical quality of fine-textured soils is generally poor due to low rate of organic matter and consequently weak stability of aggregates. A greenhouse experiment was conducted to evaluate the effects of anionic polyacrylamide (PAM) on some physical quality indices and also their temporal variability in a clay loam soil which was selected from a semiarid region in the west of Iran. These indices were mean weight diameter (MWD) of aggregates, dispersible clay ratio (DC), saturated hydraulic conductivity (Ks), and total porosity (n). The rates of PAM including 0 (control), 0.125, and 0.25 g kg-1 of air dry soil were mixed with the soil and uniformly packed into plastic pans, and incubated in a greenhouse at 0.7 to 0.8 field capacity moisture content (0.123-0.14 g g-1) and 22 ± 4 oC for 6 months . MWD, DC, Ks, and n were measured for the soil taken from the 10–15 cm layer of pans at 30, 90, and 180 days. The results showed that both low and high rates of PAM significantly increased the means of MWD by 83 and 127 % and n by 8.75 and 7.75 %, respectively compared with the control even 6 months after the start of the experiment. Also, both low and high rates of PAM significantly decreased the mean of DC by 31 and 43 % and increased the mean of Ks by 11.5 and 14.5 %, respectively relative to the control. The beneficial effects of PAM on soil physical quality were reduced with time. By considering the application cost of PAM, it can be suggested that in semiarid regions, 0.125 g PAM kg-1 of air dry soil is a suitable application rate for improving physical quality of fine-textured soils.