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Fate and Efficacy of Polyacrylamide Applied in Furrow Irrigation: Erosion and Infiltration Effects The Initial-10 treatment applied an average 1.8 kg ha I PAM (whole product) per irrigation, compared with 0.7 kg ha I for Cont-1 (Table 2). The PAM concentration in water entering Cont-1 furrows in Inrigation 1 was about one-fifth the target value, so those results from that treatment are not comparable. A total of 227 g PAM a.i. was applied to treated furrows at each irrigation (Irrigations 2, 4, 5, Continuous Treat... Page ~ TOP ~ ABSTRACT ~ INTRODUCTION ~ MATERIALS AND METHODS ~ NOTES • RESULTS AND DISCUSSION ~ CONCLUSIONS REFERENCES and 6), 27 g to each of the six Initial-10 furrows and 10.8 g to each of the six Cont-1 furrows. View this table: Table 2. Hydraulic, sediment, and polyacrylamide (PAM) application parameters. [in this windowl [in a new windowl In the first two irrigations, runoff sediment losses from untreated furrows were some of the highest observed for such fields (Lentz and Sojka, 1994, 2000). Initial-10 reduced furrow sediment loss by 74% in Irrigations 1 and 2, significantly more than the 25%reduction attained with Cont-I in Imgation 2 (Table 2). In this experiment, Initial-10 did not control sediment losses in the first two irrigations as successfully as the 92% previously observed by Lentz and Sojka (2000), even though their PAM applications continued for only 0.5 h after advance. Relative to that in the first two irrigations, erosion in subsequent irrigations was less and both Initial-10 and Cont-1 treatments were more effective in controlling sediment losses. In Irrigations 4, 5, and 6, Initial-10 reduced furrow sediment loss by 92% and Cont-1, 70%. In early irrigations, PAM treatment had no effect on furrow infiltration (Table 2). However, an analysis combining data from In•igations 2, 4, 5, and 6 showed that cumulative infiltration, as a percent of the total water applied, differed among treatments (P = 0.0001). The average cumulative infiltration for the treatments in decreasing order was: Cont-1 (59%) > Initial-10 (51 %) > Controls (47%). These results confirmed that the low-concentration continuous PAM treatment produced a lazger net furrow infiltration increase than Initial-10, relative to untreated furrows (Lentz and Soika, 2000). Santos and Serralheiro (2000) reported that the cumulative infiltration of their Cont-1 treatment trended higher than that of Initial-10, but could not establish a statistical separation. Polyacrylamide Concentration in Furrow and Tail-Ditch Streams Data from monitored Irrigations 2, 4, 5, and 6 were included in the statistical analysis because both PAM treatments in these irrigations met the concentration targets. For these irrigations, furrow stream PAM concentration differed significantly depending on main effects, that is, PAM treatments, furrow field positions, and time. The main-effect interaction terms were also significant for all irrigations, except position by time for Irrigations 5 and 6, and treatment by position by time for Irrigation 5 (Table 3). View this table: Table 3. The influence of polyacrylamide (PAM) treatment, field position (POS: upper, [in this windowl middle, and bottom locations in furrows), and sampling time during irrigation (TIME: 2, 3, [in a new window] and 7 h into the irrigation) on PAM concentration and mass-loss rates in furrow streams. Table gives P values for main effect and interaction terms that were derived from an analysis of variance. While polymer was still being applied to Initial-10 furrows at 2 h, stream PAM concentration was 6 to 8 mg L-~ at http://j egscijournals.org/cg>/content/full/31 /2/661 9/21 /2006