Water and erosion management with multiple applications of polyacrylamide in furrow irrigation

Polyacrylamide (PAM) in furrow irrigation water eliminates 94% of runoff sediment. Higher infiltration (15-50%) can result in upper-field overirrigation. We hypothesized that PAM would lengthen advance time, but that interactions with flow rate and wheel-track (WT) furrows would occur, influencing erosion and infiltration with potential for improved water management. A 2-yr study conducted on 1.5% slope Portneuf soil (Durinodic Xeric Haplocalcid) was irrigated with 10 g m-3 PAM in advancing 23 L min-1 furrow streams (reduced to 19 L min-1 after advance) (PAM treatment, P) or without PAM (control, C). Initial inflows in 1994 were 23 L min-1 (normal flow rate, N) or 45 L min-1 (high flow rate, H) with or without PAM. The application of PAM at 23 L min-1 (PN) increased 2-yr mean advance time 33% and reduced runoff soil loss 88% compared with controls (CN). Polyacrylamide applied at 45 L min-1 (PH) reduced advance time 8% and soil loss 75% compared with CN, whereas untreated 45 L min-1 inflows (CH) cut advance time 42% but raised soil loss 158%. The CH and PH raised infiltration 11 and 35% more than CN respectively. Polyacrylamide halted erosion in all furrows, but in WT furrows had no effect on advance time and little infiltration effect after two or three irrigations. This is mainly attributed to erosion and deposition increasing control-furrow wetted perimeters; accumulated PAM may also slightly affect seal conductivity. Polyacrylamide raised aggregate stability from 54 to 80% in 1993 and from 63 to 84% in 1994. In 1994, PAM reduced soil strength in furrows from 1.7 to 1.1 Mpa