Polysaccharide and salt effects on infiltration and soil erosion. A rainfall simulation study

Abstract

Seals forming at the soil surface during rainstorms reduce water penetration and increase runoff in many arid and semi-arid regions. The effect of surface application of an anionic polysaccharide (designated F-Ac), synthesized by the filamentous cyanobacterium Anabaenopsis circularis PCC 6720, on infiltration rate (IR), runoff and erosion of three soils during simulated rainstorms, was studied. The interaction between F-Ac and electrolyte concentration at the soil surface was studied by using distilled water (DW) or tap water (TW) or by spreading phosphogypsum (PG) on the soil surface. F-Ac added at the rate of 3.4 kg ha−1 together with PG at the rate of 5 t ha−1 was the most efficient treatment in improving infiltration and reducing runoff and erosion. This treatment reduced runoff, from the three soils studied, from 65–80% in the control to 14–24%. Soil loss was reduced from 3.6–4.5 Mg ha−1 in the control to 0.5–1.3 Mg ha−1 in the treated soils. DW treatment, singly and in combination with F-Ac, was quite inefficient in preventing seal formation and in reducing runoff and soil loss. Adding F-Ac with TW maintained final IR and runoff levels intermediate between those of F-Ac with PG and those of F-Ac with DW. Electrolytes in the soil surface which flocculated soil clay, enhanced the beneficial effect of F-Ac on aggregate stability and thus greatly reduced water and soil losses. The efficacy of F-Ac as a stabilizing agent (i.e., soil conditioner) wore out during three consecutive storms of 60 mm each.