The agricultural use of polyacrylamide, PAM, as an additive
in irrigation water has grown rapidly since commercial
introduction in 1995, with over l million acres treated in 1998.
PAM provides both economic and environmental benefits by
improving water infiltration and reducing up to 98% of erosion-induced
soil losses — a yearly saving of tons of topsoil per acre.
With as little as 5 ppm of PAM in the first irrigation water to run
across the field, soil cohesion increases enough to prevent
particle detachment and erosion. Stable soil/polymer flocs result
from PAM's high molecular weight (typically > 12 million) and
its affinity to soil via coulombic and Van der Waals attraction.
Although water soluble linear PAM is the only class of
commercial polymer presently used to reduce erosion during
irrigation, other polymer additives have shown some potential.
Biopolymers such as chitosan, starch xanthate, cellulose
xanthate, and acid-hydrolyzed cellulose microfibrils reduce
shear-induced erosion; however concentrations at least 6-10
times higher than PAM are required to obtain the > 90% runoff
sediment reduction shown by commercial PAM. The application
of PAM in agricultural irrigation water and potential biopolymer
alternatives to PAM are discusse
