USE OF CHEMICALS IN SWCUSE OF CHEMICALS IN SWC

Soil chemical treatmentsSoil chemical treatments

Wetting agentsWetting agents

• hydrophobic soilshydrophobic soils• allow allow infiltration on soils which are naturally infiltration on soils which are naturally

resistantresistant• surfactants – reduce surface tensionsurfactants – reduce surface tension• Anionic surfactantsAnionic surfactants

• Ammonium Lauryl Ether SulphatesAmmonium Lauryl Ether Sulphates• Sodium Lignosulphonates Sodium Lignosulphonates • Sodium alkyl sulphosuccinates Sodium alkyl sulphosuccinates

http://www.soil.ncsu.edu/publications/Soilfacts/AG-http://www.soil.ncsu.edu/publications/Soilfacts/AG-439-25/439-25/

• Nonionic surfactants• Nonyl Phenol Ethoxylates • Alcohol Alkoxylates • lower molecular weight chemcials may be phytotoxic

• Polymeric nonionic surfactants • Ultra-penetrantsUltra-penetrants

Hydrophilic soil conditionersHydrophilic soil conditioners

• absorb many times their own weight of water but absorb many times their own weight of water but release it at the range of potentials prevailing in release it at the range of potentials prevailing in the soilthe soil

• increase AWC, reduce drainage losses, increase AWC, reduce drainage losses, • e.g. Agrosoak and polyacrylamidee.g. Agrosoak and polyacrylamidehttp://www.nal.usda.gov/wqic/Bibliographies/http://www.nal.usda.gov/wqic/Bibliographies/

eb9614.htmleb9614.html

• Polyvinyl acetate effective in semi-arid areas - Polyvinyl acetate effective in semi-arid areas - reduced runoff by 84 to 97% in one experiment.reduced runoff by 84 to 97% in one experiment.

Structure improving chemicals• very high molecular weight, long-chain, polymeric,

organic compounds,• bind particles together and form stable aggregates• natural polysaccharides, • anionic and cationic polymers, • polyacrylamides• urea-poly-condensate

Natural materials to improve structureNatural materials to improve structureCalcified SeaweedCalcified Seaweed• dead remains of calcareous red algae (Rhodophyta)dead remains of calcareous red algae (Rhodophyta)• improves clay structure - flocculation improves clay structure - flocculation • improves water holding capacity – silt sizeimproves water holding capacity – silt size

CoirCoir

PVAPVA

Reducing percolation lossesReducing percolation losses

• Insert impermeable membrane below root zone, Insert impermeable membrane below root zone, • e.g. plastic, bitumen, rubbere.g. plastic, bitumen, rubber

• expensiveexpensive

• risk of salinisation/drainage problems increasedrisk of salinisation/drainage problems increased

• may reduce fertiliser requirement by reducing may reduce fertiliser requirement by reducing percolation lossespercolation losses

Evaporation suppressorsEvaporation suppressors

• Emulsion of water and oil/wax. e.g. hexadecanol, Emulsion of water and oil/wax. e.g. hexadecanol, bitumen, asphalt, latexbitumen, asphalt, latex

• polydimethylsiloxane polydimethylsiloxane

• bind soil, reduce wind & water erosion, & bind soil, reduce wind & water erosion, & evaporationevaporation

• may increase runoff, possibly useful for Water may increase runoff, possibly useful for Water Harvesting (see later)Harvesting (see later)

• may cause pollution problemmay cause pollution problem

• expensiveexpensive

Infiltration inhibitorsInfiltration inhibitors

• chemicals, e.g. salt sometimes used to chemicals, e.g. salt sometimes used to increase runoff from unplanted part of increase runoff from unplanted part of catchment to increase effective rainfall on catchment to increase effective rainfall on planted part (see section on water planted part (see section on water harvesting)harvesting)

• waxwax• bitumenbitumen

Chemical treatment of plantsChemical treatment of plants Albedo increasers (reflective transpirationAlbedo increasers (reflective transpiration suppressants)suppressants)

• white to reflect solar radiationwhite to reflect solar radiation• kaolin - cuts solar heating & air turbulencekaolin - cuts solar heating & air turbulence• may reduce insect pest damagemay reduce insect pest damage• must be non-toxic/palatablemust be non-toxic/palatable• may reduce yields by clogging stomata, or may reduce yields by clogging stomata, or

reduction of photosynthesisreduction of photosynthesis

Metabolic transpiration suppressantsMetabolic transpiration suppressants• physical barriersphysical barriers

• wax, silicone, latex sprayed onto leaveswax, silicone, latex sprayed onto leaves• systemic (herbicides)systemic (herbicides)

• alachloralachlor• atrazineatrazine