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Fate and Efficacy of Polyacrylamide Applied in Furrow Irrigation: Full-Advance and Continuous Treat... each top, middle, and bottom furrow position. Initial-10 effectively controlled erosion and maintained low mean furrow stream sediment concentrations, averaging 0.2 mg L-~ (Table 4). Thus, little sediment was available to adsorb the polymer, and furrow stream PAM concentrations remained unchanged as the flow crossed the field. Thirty minutes after Initial-10 application ceased, the furrow stream PAM concentration had decreased to undetectable levels, with the exception of Irrigation 6 (Fie. 2) . It is not cleaz why PAM concentrations in Imgation 6 at 3 h and 7 h did not decline to near zero, as occurred for previous inrigations. The response was not restricted to one or two furrows. It was consistent across all replicates. View this table: Table 4. Runoff and sediment for polyacrylamide (PAM)-treated furrow and the tail-water [in this windowl streams (mean of three sampling positions). [in a new windowl ._...~. ti _ ..- ........... ~.c ~. .. ~ .;;~ -- ~ °I ~I : t_ -----•- ----~ ~ _ - -- 1 h.~, .., -- ~ ~ ~~~ .~ a;,...a.,....,.M View larger version (42K): [in this windowl [in a new windowl Fig. 2. Polyacrylamide (PAM) concentrations in Initial-10 furrow streams, by sampling position and time. Polyacrylamide was being applied at 2 h into the irrigation, but was stopped approximately 30 min prior to the 3-h sample time. Note break and change in y axis scale. MDL, method detection limit. Compazed with the Initial-10, PAM concentration in the Cont-1 treatments changed less abruptly between sampling times during irrigation, but changed more with sampling position. At 2 h, inflow PAM concentration for Cont-1 furrows was 0.9 mg L-~ a.i. (Fie. 3) and mean stream sediment concentrations were nearly 40 times greater (Table 4) than for Initial-10 furrows. The greater sediment availability increased PAM adsorption onto entrained soil and decreased PAM concentration in the stream as it flowed across the field. Thus, 2-h Cont-1 furrow-stream PAM concentrations had declined to undetectable levels by the time the flow had traveled to the mid-furrow position. Fig. 3. Polyacrylamide (PAM) concentrations in Cont-1 furrow streams by sampling position and time for similar monitored irrigations. MDL, method detection limit. http://jeq.scijoumals.org/cgi/content/fulU31/2/661 9/21/2006