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Deep Percolation and Preferential Flow Under Conventionally and PAM-Treated Irrigation Furrows
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Pp. 157-160 in Preferential Flow, Water Movement and Chemical Transport in the Environment, Proc. 2nd Int. Symp. (3-5 January 2001, Honolulu, Hawaii, USA), eds. D. D. Bosch and K. W. King. St. Joseph, Michigan: ASAE 701P0006.(doi:10.13031/2013.2113)
Authors: R.D. Lentz
Keywords: bypass flow, infiltration, erosion, polyacrylamide
Water-soluble anionic polyacrylamide (PAM), a nontoxic polymer, is employed in furrow irrigation to control soil erosion and increase infiltration. We hypothesized that post-irrigation deep percolation and preferential-flow patterns for the PAM treatment would differ from that of the conventionally irrigated (CI) furrows. Portneuf silt loam plots 179 m long were planted to corn and irrigated using either CI or PAM treatment. We added PAM to advancing irrigation furrow streams at10 ppm. Inflow rates during furrow advance were 3X greater than that of conventionally irrigated furrows. Vacuum assisted percolation samplers at 1.2 m depth and neutron probe access tubes were installed at locations 30 m down furrow to monitor soil water flux and soil wetting patterns. Daily deep percolation volumes were collected after two irrigation events in 1998, and analyzed for nitrate-N and Cl concentrations. Two general patterns for daily percolation rate emerged. Under CI, percolation rate started high the first day after irrigation, declined during the second and third days to a value about half that of the first day, then rose to a second peak between 6 and 7 days after irrigation. PAM percolation rate started low on the first day after irrigation, peaked at about twice the initial rate on day two or three, declined through day four or five, then rose to a second peak between 6 and 8 days after irrigation. Water moved rapidly downward from CI furrows after irrigation, and included bypass flow that diluted nitrate concentrations in deep percolation water. PAM treatment inhibited initial rapid downward movement of applied water, possibly by reducing preferential flow.
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