Reducing Furrow Irrigation Erosion with Polyacrylamide (PAM)

Abstract

There has been a large shift to sprinkler irrigation in the USA. Beyond laborconsiderations, this has been driven by soil and water resource conservation.Some crops, however, do not tolerate wet canopies (e.g., seed beans). Further-more, the capital cost, energy use, and technological requirements are out of thereach of many U.S. and third world irrigators. If inexpensive, effective, easyerosion control were available, many furrow irrigation farmers could improveresource conservation and water management.Small amounts of a specific class of polyacrylamide (PAM) copolymer can vir-tually halt furrow irrigation-induced erosion. Net infiltration is also improved(infiltration rate does not decline, compared with untreated water) while man-agement options are broadened. Various copolymer formulations of water-solu-ble PAM and other copolymers have been available for soil-stabilization in agri-culture since the 1950s. While these conditioners were effective at stabilizingsoil structure and improving infiltration, early materials and high applicationrates were prohibitively expensive for all but high-return uses.In 1991, work by the USDA's Agricultural Research Service in Kimberly, ID,demonstrated that 1 lb/acre of moderate molecular weight (12-15 Mg/mole)anionic polyacrylamide water soluble copolymer could virtually halt furrowirrigation-induced erosion. Treatment required dissolving PAM at a concentra-tion of 10 ppm in the irrigation water during its initial traverse down the dryfurrow (advance). The treatment has proven consistently effective for a varietyof soils and textures on freshly tilled furrows having slopes of as much as 7%.Net infiltration rates are also improved, with increases ranging from 15% in siltloam soils to 50% in clayey soils.Extensive testing in Idaho, complemented by studies in several other westernstates, led in 1994 to commercial product registration in most western states. InJanuary 1995, the Natural Resources Conservation Service (NRCS) published awestern states interim conservation practice standard to describe preferredmethodology. Practice adoption in 1995 was estimated at 50 000 acres in theUSA, predominantly the Pacific Northwest. A number of locales now have costsharing for the practice.There is intense user interest in implementation and further development of thisapproach. Emphasis of recent research and farmer inquiries has been focused ondevelopment of easy application technology, minimization of PAM requirement,and verification of PAM's inherent resistance to off-field migration.