REDUCING FURROW IRRIGATION EROSION WITH POLYACRYLAMIDE (PAM)

Irrigated cropping is a critical component of global agricultural prod uction. Surface irrigation-most of it furrow irrigation-accounts for > 60% of Earth's 600 million irrigated acres. Erosion threatens irrigati on's ability to maintain its 2X average yield advantage and 3X value o ver rainfed agriculture, with serious environmental and food security consequences to the burgeoning human population. Furrow irrigation-ind uced erosion is nearly halted by small additions of water-soluble poly acrylamide (PAM) to irrigation water. PAM is an environmentally safe f locculent used extensively in municipal water treatment, paper manufac turing, food processing, and other sensitive applications. On freshly cultivated furrows, 1 lb/acre of PAM applied at 10 ppm in irrigation w ater before runoff began (only), reduced sediment loss in runoff 94% a nd increased net water infiltration 15% in 3 yr of Idaho tests on silt loam soils. Irrigation return-flow quality was improved by PAM-use, g reatly reducing sediment losses, biochemical oxygen demand (BOD), tota l P, and various pesticides. Polyacrylamide products are now registere d in most western states and the Natural Resources Conservation Servic e (NRCS) has published a PAM-use practice standard. Cost sharing is av ailable in some locales. In 1995 about 50 000 acres of furrow-irrigate d land used PAM, halting as much as 1 million tons of soil erosion in the first year. Farmers see PAM-use as an attractive alternative to mo re difficult conservation practices. The typically $15 to $35/acre per crop costs are partially or entirely retrieved by crop responses or s avings in erosion-related field operations and water conservation. Pam -use in irrigation is expected to expand rapidly in 1996.