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Fate and Efficacy of Polyacrylamide Applied in Furrow Irrigation: Full-Advance and Continuous Treat... Page 4 of 16 <br />Two PAM treatments were compared: the Initial-10 and the alternative Cont-1. Note that the Initial-10 treatment <br />applied PAM for 1.2 to 2 h longer than recommended by the NRCS standard, which curtails PAM application <br />immediately after runoff begins. This extended application allowed time for furrow stream PAM concentration to <br />approach equilibrium, facilitated simultaneous sampling, and ensured uniform tail-water flow conditions across all <br />irrigations. Hence, we used nearly two times more PAM here than is typically applied in Initial-10 treated irrigations <br />(Table 1). Of seven imgations applied, five were treated and monitored, including sampling of furrow and wastewater <br />streams for PAM analysis (Table 1). <br />View this table: Table 1. Irrigation parameters for study. Polyacrylamide (PAM) Initial-10 added an <br />[in this windowl aqueous PAM solution to initial irrigation inflows at 10 mg L-t (whole-product basis), and <br />[in a new windowl Cont-1 applied 1 mg L-~ PAM during the entire irrigation. <br />The completely randomized design consisted of a control and two PAM application treatments. The experimental unit <br />was a single irrigation furrow. Samples for PAM analysis were taken from each treated furrow at three positions, 3 m <br />(top), 76 m (middle), and 167 m (bottom) downstream from the inflow end (F1E. 1) .The samples were collected from <br />the end of flumes placed in the furrows. Samples were taken at three times during the irrigation, at approximately 2, 3, <br />and 7 h into the irrigation set. For the Initial-10, treatment times corresponded to -0.5, 0.5, and 5 h after the PAM <br />application was curtailed. Therefore, for each irrigation, PAM furrow stream data comprised (2 PAM treatments) by <br />(3 positions) by (3 times) by (6 replicates) = 108 samples. The PROC MIXED procedure (SAS Institute 1997) was <br />used to fit asplit-split plot model separately for each irrigation; with treatments as main plots, positions as subplots, <br />and time as sub-subplots. Degrees of freedom used in confidence intervals on the treatment by time by position means <br />were adjusted by Huynh-Feldt e values to account for lack of sphericity in the covariance structure across time. To <br />stabilize variances, a square root transformation was applied to concentration and mass-loss values, after adding a <br />small constant to avoid negative values. <br /> !' 'III ~I',i rnnn <br />~~ ~~ I <br />~~ <br />I <br />.rrma <br /> i <br />~ <br />r..rmn <br /> • Wen <br />rMNr4111' ~Ttl <br />l <br />~ wnn J wives rn.n <br /> \-_i ~•.. <br /> ual~H <br /> err <br />~. rr <br />Y ~ r~nPNlnm <br /> w rmp <br />View larger version (32K): <br />[in this windowl <br />[in a new windowl <br />Fig. 1. Field plot showing sampling locations in furrows and tail-ditch <br />streams. <br />During an irrigation, runoff from all six furrows (replicates) per treatment including controls passed into a collection <br />ditch oriented perpendicular to the furrows (Fie. 1). The combined flow then entered a 530-m-long tail ditch. <br />Occasional tail-water contributions from neighboring farms entered the tail ditch at locations >274 m down the ditch. <br />The tail ditch was newly formed prior to the first irrigation, but left undisturbed (except for irrigation) for the <br />http://jegscijournals.org/cgi/contendfulU31 /2/661 9/21 /2006 <br />