Polyacrylamide effects on infiltration in irrigated agriculture

Using polyacrylamide (PAM) following the NRCS conservation practice standard increases infiltration in furrow irrigation. PAM at 10 g in-' (10 ppm) during water advance nearly precludes detachment and transport of soil in furrows. If any sediment is entrained in the flow, it is readily flocculated in the presence of PAM and settles to the furrow-bottom in loose pervious structures. It was hypothesized that depositional surface seals that block pores are reduced or made more permeable with PAM. On Portneuf silt beams (coarse-silty, mixed, superactive, Durinodic Xeric Haplocalcid) furrow irrigation net infiltration increased 15%. Net increases on finer textured soils were generally higher. Furrow streams containing more than 5 g L (5,000 ppm) sediment reduced infiltration and infiltration rate more than fivefold compared to streams of clean water. Tension infiltrometry confirmed that PAM's maintenance of open pores to the furrow surface provides the infiltration increase mechanism. Infiltration rates at 40 and 100 min (1.6 and 3.9 inches) tension in PAM-treated furrows were double the rates of control furrows. Recirculating infiltrometer data showed a 30% infiltration increase with PAM use and infiltration was inversely related to maximum sediment concentration in the flow. Furrow inflow of 45 L min-1 (12 gal min-1 ) with PAM treatment decreased stream advance time 13% while reducing sediment loss 76% compared to untreated 23 L min-1 (6 gal min-1) inflows. Use of PAM in sprinkler irrigation streams reduced runoff 70% and sediment loss 75%, but tension infiltration measurements were inconsistent, suggesting changes in surface-sealing effects with sprinkler application of PAM are transient