High levels of soil sodicity, resulting from intensive irrigation with
saline-sodic waters, lead to an increased soil susceptibility to seal
formation and to severe problems of runoff and soil erosion. The obje
ctive of this study was to investigate the efficacy of the addition of
small amounts of an anionic polyacrylamide (PAM) to the irrigation wa
ter in controlling seal formation, runoff and soil erosion. Two predom
inantly montmorillonitic sails were studied, a grumusol (Typic Haploxe
rert) and a loess (Calcic Haploxeralf), having naturally occurring exc
hangeable sodium percentage (ESP) >12. The soils were exposed to 60 mm
of simulated irrigation with commonly used tap water (TW, electrical
conductivity=0.8 dS m(-1); sodium adsorption ratio (SAR)=2), or saline
water (SW, electrical conductivity=5.0 dS m(-1);SAR>12). PAM effectiv
eness in controlling runoff and erosion from the sodic soils was compa
red with runoff and erosion levels obtained from untreated soils havin
g low ESPs (<4). For both soils and for both water qualities and polym
er concentrations in the irrigation water, PAM was efficient in contro
lling runoff at low ESP levels and inefficient at high ESP levels. At
moderate ESP levels, PAM's efficacy in controlling runoff was inconsis
tent and varied with water quality and polymer concentration. Converse
ly, in general, soil loss originating from rill erosion, was significa
ntly and effectively reduced in moderate and high ESP soils by additio
n of PAM to the irrigation water, irrespective of water quality and po
lymer concentration. PAM was more effective in reducing rill erasion t
han in reducing runoff in the moderate and high ESP samples, because t
he energy involved in generating runoff is much higher than that invol
ved in rill erosion. PAM treated surface aggregates were not stable ag
ainst the distructive forces leading to seal formation and runoff prod
uction; but they were stable enough to resist the hydraulic shear exer
ted by the runoff flow.