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Fig. 18.12 Application of polysaccharide (PS), phosphogypsum (PG), and polysaccharide with
phosphogypsum (PS + PG) on soil versus runoff, in comparison with untreated site (C). Percent
runoff for three consecutive 60 mm rainstorms (modified after Warrington et al. 1991 ) Reprinted
from Warrington et al. ( 1991 ). Copyright 1991 with permission from Elsevier
Polysaccharides (PSDs) of anthropogenic origin form another group of organic
polymers used to prevent or diminish clay particle dispersion and erosion of soils
caused by aggregate stabilization and increasing infiltration rate. Ben-Hur and
Letey ( 1989 ) showed that the type of polysaccharide has a significant effect on the
change in infiltration rate (IR); of the polymers tested, only the anionic compound
had no effect. The final IR values of the efficient amendments were 19.0, 14.2, and
5.2 mm/h, compared with 4 mm/h for the untreated soil. These results suggest that
the electrostatic adsorption of the PSDs on the negative soil-clay surface was the
dominant factor in providing stability to the aggregates and a change in the
infiltration rate. Furthermore, the soil IR change induced by low charge cationic
polymer addition to water during the first application was partially maintained
during succeeding untreated water applications, demonstrating stability of soil
aggregates against the energy impact of rain/irrigation drops (Ben-Hur et al. 1989 ).
Another essentially irreversible effect of PSD application is the prevention of
soil runoff that occurs as a result of seal formation at the soil surface during
rainstorms. Warrington et al. ( 1991 ) reported changes in runoff patterns of soils
from arid and semiarid areas, as a result of application of an anionic acidic
polysaccharide (F-AC) of algae extracellular origin, with a molecular weight of
*70,000 g/mol. The effects on runoff reduction of PSD applied individually or
associated with electrolytes released by phosphogypsum dissolution, in three
consecutive simulated rains, are shown in Fig. 18.12 . A lasting and marked effect
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