The beating action of rain or sprinkler drops causes the breakdown of
aggregates and clay dispersion, which subsequently leads to seal forma
tion. Seal formation reduces infiltration rate and generates high leve
ls of runoff. Chemical soil amendments (e.g., phosphogypsum, organic p
olymers) can improve aggregate stability and limit clay dispersion and
thus prevent seal formation. This review discusses the effects of org
anic polymers on controlling seal formation as characterized by change
s in soil infiltration rate and dependence on soil properties. Soil su
sceptibility to sealing depends on a number of soil properties, includ
ing soil texture and mineraology, composition of the exchangeable cati
ons, and water quality. Addition of small amounts of polymers (10-20 k
g ha-1), either sprayed directly onto the soil surface or added to the
applied water, stabilizes and cements together aggregates at the soil
surface, thereby increasing their resistance to seal formation. The i
nfiltration rate of a polymer-treated soil subjected to distilled wate
r rain is two or three times that of a non-treated soil. The efficacy
of anionic polymers in preventing seal formation is enhanced when the
soil clay is maintained in a flocculated state. The latter is achieved
by addition of electrolytes (either in the ''rain'' water or phosphog
ypsum addition) in the soil solution at the soil surface. Combined app
lication of anionic polymers with electrolytes results in final infilt
ration values of approximately 25 mm h-1, which are 10 times higher th
an the control. Polymer effectiveness in controlling seal formation de
pends also on charge type and density and on the molecular weight of t
he polymer. The effect of polymers and water quality on seal formation
is in good agreement with the effect of the polymers on the flocculat
ion patterns of soil clays. Of the polymers currently available and un
der study, anionic polyacrylamide has been found to be the most effect
ive in controlling seal formation, and soil erosion and has the longes
t residual effect.