Water and erosion management with multiple applications of polyacrylamide in furrow irrigation.
 
(A brief summary of work to appear soon in the Soil Science Society of America Journal)
 
R.E. Sojka,  R.D. Lentz, and  D.T. Westermann
 
Soil Scientists, USDA Agricultural Research Service, Northwest Irrigation and Soils Research Laboratory, 3793N-3600E, Kimberly, ID 83301. Phone: 208-423-5582  FAX 208-423-6555.
 
Acknowledgement
This work was partially funded through USDA CRADA #58-3K95-4-216, with our CRADA partner CYTEC Industries. The authors would also like to acknowledge Mr. James Foerster, Mr. Ronald Peckenpaugh, Miss Shirley Bosma, and Mrs. Mary Ann Kay for their dedicated work and unfaltering technical support in the execution of this project.
 
ABSTRACT
Polyacrylamide (PAM) in furrow irrigation water eliminates 94% of runoff sediment. Higher infiltration (15-50%) can result in upper-field over-irrigation.  We hypothesized that PAM would lengthen advance time but that interactions with flow rate and wheel-track furrows would occur, influencing erosion and infiltration with potential for improved water management.  A 2 yr study conducted on 1.5% slope Portneuf soil (Durinodic Xeric Haplocalcids) was irrigated with (P) or without (C) 10 g m-3 PAM in advancing 23 L min-1 furrow streams (reduced to 19 L min-1 after advance).  Initial inflows in 1994 were 23 L min-1 (N) or 45 L min-1 (H) with or without PAM.  The application of PAM at 23 L min-1 (PN) increased 2 yr mean advance time 33% and reduced runoff soil loss 88% compared to controls (CN).  PAM applied at 45 L min-1 (PH) reduced advance time 8% and soil loss 75% compared to CN, whereas untreated 45 L min-1 inflows (CH) cut advance time 42% but raised soil loss 158%.  CH and PH raised infiltration 11% and 35% over CN respectively.  PAM halted erosion in all furrows but in wheel-track furrows had no effect on advance time and little infiltration effect after 2 or 3 irrigations.  This is mainly attributed to erosion and deposition increasing control furrow wetted perimeters; accumulated PAM may also slightly affect seal conductivity.  PAM raised aggregate stability from 54 to 80% in 1993 and from 63 to 84% in 1994.  In 1994 PAM reduced soil strength in furrows from 1.7 to 1.1 MPa.
 
ABBREVIATIONS
PAM (polyacrylamide); DOY (Day of Year); ppm (parts per million); CN (Control Normal Flow Rate); CH (Control High Flow Rate); PN (PAM-treated Normal Flow Rate); PH (PAM-treated High Flow Rate); NW (Non-Wheel); WT (Wheel-track)
 

This paper is IN PRESS for Soil Sci. Soc. Am. J.
 

FIGURES
Click for big Fig 1 (47Kb) Figure 1. Seasonal sediment losses per treatment per irrigation in furrow outflows in 1993 and 1994, as affected by PAM addition (P) or untreated water (C), normal (N) or high (H) flow rate, and wheel-track (WT) vs non-wheel (NW) furrow. 
Click for big Fig 2 (50Kb) Figure 2. Seasonal advance times in 1993 and 1994, as affected by PAM addition (P) or untreated water (C), normal (N) or high (H) flow rate, and wheel-track (WT) vs non-wheel (NW) furrow. 
Click for big Fig 3 (50Kb) Figure 3. Seasonal net infiltration amounts in 1993 and 1994 as affected by PAM addition (P) or untreated water (C), normal (N) or high (H) flow rate, and wheel-track (WT) vs non-wheel (NW) furrow. 
Click for big Fig 4 (43Kb) Figure 4. Estimate of PAM (P) at normal (N) or high (H) flow rate and wheel-track (WT) or non-wheel (NW) effects on set-time excess or set-time deficit, relative to water amount delivered in the CN treatment of the respective WT or NW furrow each year, based on net infiltration of the CN treatment and the final infiltration rate of the corresponding PAM-treated furrows. 

Table 1. Total seasonal furrow inflow, outflow, infiltration and sediment loss, and mean advance time for non-wheel furrows, wheel-track furrows, or combined. Because wheel-track and non-wheel irrigations were separate events, all three presentations required separate statistical analysis (Table 2).
 
Seasonal Hydraulic Summary
Inflow Outflow Infiltration Sediment Loss Advance Time
---------mm-------- --------mm-------- --------mm-------- --------kg ha-1-------- ----------min----------
NW WT NW+WT NW WT NW+WT NW WT NW+WT NW WT NW+WT NW WT Mean
1993
PN 331 
(24)†		 295 
(1)		 626 
(25)		 59 
(7)		 101 
(11)		 160 
(11)		 272 
(30)		 195 
(10)		 466 
(27)		 124 
(63)		 71 
(26)		 195 
(70)		 157 
(98)		 91 
(53)		 121 
(83) 
CN 317 
(4)		 295 
(1)		 613 
(5)		 67 
(5)		 107 
(5)		 173 
(6)		 250 
(9)		 189 
(5)		 439 
(8)		 674 
(153)		 3705 
(700)		 4379 
(697)		 100 
(37)		 89 
(42)		 94 
(40) 
1994
PN 718 
(50)		 553 
(45)		 1271 
(95)		 97 
(26)		 255 
(23)		 353 
(46)		 620 
(55)		 298 
(31)		 918 
(86)		 65 
(56)		 534 
(249)		 599 
(242)		 159 
(62)		 73 
(25)		 115 
(64) 
CN 711 
(58)		 556 
(45)		 1267 
(103)		 177 
(36)		 225 
(49)		 402 
(79)		 534 
(37)		 331 
(8)		 865 
(30)		 2050 
(496)		 3015 
(1150)		 5065 
(770)		 92 
(68)		 78 
(24)		 84 
(50) 
PH 946 
(33)		 643 
(52)		 1589 
(85)		 120 
(87)		 305 
(45)		 425 
(122)		 826 
(61)		 339 
(23)		 1164 
(41)		 25 
(20)		 1242 
(1111)		 1268 
(1130)		 108 
(49)		 47 
(17)		 77 
(47) 
CH 866 
(36)		 635 
(52)		 1502 
(83)		 265 
(48)		 279 
(51)		 544 
(97)		 601 
(35)		 357 
(15)		 958 
(22)		 3991 
(2135)		 9060 
(4723)		 13051 
(6662)		 50 
(28)		 48 
(18)		 49 
(24) 
 
†Standard deviation is shown as (n).

Table 2. Statistics for total seasonal furrow inflow, outflow, infiltration and sediment loss, and mean advance time for non-wheel furrows, wheel-track furrows, or combined. Because wheel-track and non-wheel irrigations were separate events, all three presentations required separate statistical analysis.
 
Seasonal Hydraulic Summary Statistics, Pr>F†
Inflow Outflow Infiltration Sediment Loss Advance Time
NW WT NW+WT NW WT NW+WT NW WT NW+WT NW WT NW+WT NW WT Mean
1993
+/- PAM NS NS NS NS NS NS NS NS NS 0.0057 0.0020 0.0015 0.0445 NS 0.0394
1994
+/- PAM (P) NS NS 0.0071 NS NS 0.0217 0.0097 NS 0.0082 0.0254 NS 0.0042 0.0014 NS 0.0018
N/H Flow (F) NS NS 0.0001 NS NS 0.0077 0.0126 NS 0.0023 NS NS NS 0.0064 0.0001 0.0007
P x F NS NS 0.0109 NS NS NS 0.0469 NS NS NS NS NS NS NS NS
 
†Probability > F exceeding 5% is indicated by NS.

Table 3. The effect of PAM-treatment, field position, and wheel traffic on late season furrow width in two seasons of furrow irrigation. Field measurement locations were 62, 92, and 120 m along furrows, measured July 20 and 27, 1993 and July 7 and 11, 1994.
 
Late Season Furrow-bottom Width, cm
1993 1994
Top Mid Bottom Top Mid Bottom
PAM Wheel-track 14.1 (2.2)† 13.5 (1.9) 14.4 (1.8) 12.7 (2.1) 15.3 (1.8) 18.8 (1.8)
Non-wheel 14.9 (1.0) 12.8 (2.8) 14.1 (2.4) 15.7 (2.4) 14.7 (2.2) 16.1 (2.4)
Control Wheel-track 21.9 (4.2) 24.0 (2.6) 24.3 (2.9) 27.8 (3.1) 29.6 (1.8) 28.4 (2.5)
Non-wheel 14.6 (4.4) 19.1 (2.4) 20.4 (1.7) 20.8 (3.0) 24.4 (3.6) 24.6 (3.6)
 
†Standard deviation is shown as (n).

Table 4. The effect of PAM-treatment, field position, and wheel traffic on late season furrow width in two seasons of furrow irrigation.
 

Late Season Furrow-bottom Width Statistics, Pr>F†
1993 1994
+/- PAM 0.0003 0.0001
+/- Wheel 0.0001 0.0001
Location NS 0.0007
PAM x Wheel 0.0001 0.0001
PAM x Wheel x Location 0.0420 0.0001
 
†Probability > F exceeding 5% is indicated by NS. All factorials and interactions were tested individually and interactively, only those showing significant effects are listed.

Table 5. Percent water stable aggregates as affected by PAM-treatment, date, and distance along the furrow.
 
% Stable Aggregates
Furrow Bottom, 8-12-93 Furrow Side, 8-19-93
Distance PAM Control PAM Control
62 m 82 (5)† 42 (8) 84 (5) 57 (8)
120 m 80 (5) 48 (13) 76 (6) 68 (8)
Furrow Bottom, 7-19-94 Furrow Side, 7-19-94
Distance PAM Control PAM Control
62 m 90 (4) 36 (5) 92 (4) 69 (12)
120 m 76 (8) 47 (12) 85 (6) 78 (11)
 
†Standard deviation is shown as (n).

Table 6. Percent water stable aggregates as affected by PAM-treatment, date, and distance along the furrow.
 

% Stable Aggregates Statistics, Pr>F†
1993 1994
+/- PAM 0.0001 0.0001
Bottom/Side Position 0.0386 0.0001
62/120 m Distance NS NS
PAM x Position 0.0176 0.0008
PAM x Distance 0.0020 0.0248
Distance x Position NS NS
PAM x Position x Distance NS NS
 
†Probability > F exceeding 5% is indicated by NS. In 1994 the effect of flow rate was found non-significant, therefore flow data were pooled for further analysis.

Table 7. Effects of wheel traffic, distance down the furrow, water inflow rate and PAM treatment on depositional crust strength in two seasons. In 1993 soil water was only measured in wheel track furrows.
 
Strength of Depositional Crusts in Furrows
1993 Non-wheel
CN PN mean
Distance MPa H2O% MPa H2O% MPa H2O%
62 m 1.39 (0.64)† 1.32 (0.81) 1.35 (0.72)
120 m 1.35 (0.68) 1.35 (0.78) 1.35 (0.72)
Traffic mean 1.37 (0.65) 1.33 (0.78) 1.35 (0.71)
1993 Wheel-track
62 m 1.06 (0.55) 22.0 (1.7) 1.08 (0.64) 22.4 (0.8) 1.07 (0.59) 22.2 (1.3)
120m 0.87 (0.59) 27.5 (5.3) 0.79 (0.41) 22.9 (2.7) 0.83 (0.50) 25.2 (4.7)
Traffic mean 0.96 (0.57) 25.7 (5.1) 0.94 (0.55) 22.7 (2.2) 0.95 (0.55) 24.2 (3.2)
PAM mean 1.14 (0.63) 1.11 (0.68)
 
1994 Non-wheel
CN CH mean PN PH mean
Distance MPa H2O% MPa H2O% MPa H2O% MPa H2O% MPa H2O% MPa H2O%
62m 1.17 (0.75) 16.9 (9.6) 1.19 (0.73) 21.2 (17.2) 1.18 (0.72) 19.0 (13.7) 0.56 (0.26) 16.4 (7.9) 0.66 (0.44) 17.0 (8.9) 0.61 (0.35) 16.7 
(8.1)
120m 0.60 (0.30) 21.8 (7.9) 0.76 (0.38) 20.5 (8.6) 0.68 (0.34) 21.1 (8.1) 0.64 (0.20) 16.9 (5.6) 0.61 (0.23) 18.8 (6.8) 0.63 (0.21) 17.8 
(6.1)
Flow mean 0.88 (0.63) 19.3 (8.9) 0.97 (0.60) 20.8 (13.2) 0.60 (0.23) 16.6 (6.6) 0.64 (0.34) 17.9 (7.7)
PAM mean 0.93 (0.61) 20.1 (11.1) 0.62 (0.29) 17.3 
(7.1)
 
†Standard deviation is shown as (n).

Table 8. Effects of wheel traffic, distance down the furrow, water inflow rate and PAM treatment on depositional crust strength and water content in two seasons.
 

Strength of Depositional Crusts in Furrows: Statistics, Pr>F†
Soil Strength Water Content
1993 1994 1993 1994
+/- PAM NS 0.0005 NS NS
Distance 0.0252 0.0001 0.0414 NS
PAM x Distance NS 0.0001 NS NS
Traffic 0.0001 NA NA NA
Traffic x Distance 0.0477 NA NA NA
Traffic x PAM NS NA NA NA
Traffic x PAM x Distance NS NA NA NA
Flow Rate NA NS NA NS
Flow Rate x Distance NA NS NA NS
PAM x Flow Rate NA 0.0001 NA NS
PAM x Flow Rate x Distance NA 0.0486 NA NS
 
†Probability > F exceeding 5% is indicated by NS. All factorials and interactions were tested individually and interactively, only those showing significant effects are listed.

 
CONCLUSIONS
         Furrow irrigation can benefit from the management flexibility PAM provides while reducing erosion.  PAM can be used to greatly increase inflows yet still greatly reduce sediment loss.  The smaller infiltration opportunity time disparity between upper and lower field ends achievable with use of higher inflow rates can help prevent over-irrigation and leaching at upper ends of frequently irrigated fields.  To fully realize this strategy requires reduction of inflows to minimum sustainable flows once runoff begins.
         PAM-use per se did not increase advance time or infiltration in wheel track furrows compared to non-treated wheel-track furrows after the first 2-3 irrigations.  This is most likely due to furrow alterations occurring in the untreated furrows as a result of erosion, but may indicate some effect of PAM on pore conductivity with repeated application of PAM.  This phenomenon deserves further study.  PAM applied at only 5 g m-3 after several 10 g m-3 applications continued to prevent erosion substantially compared to controls.
         Measurements of strength of the depositional crust in furrows and of the aggregate stability of soil in furrow bottoms and along furrow sides support the conclusion that PAM's hydraulic and erosional effects result largely from structural stabilization of the thin surface veneer of soil in these locations, preventing surface sealing.  Stabilization of structure is readily apparent in aggregate stability, but, as would be expected, is less consistently manifest in strength of the furrow-bottom depositional crust.  The increase in aggregate stability prevents formation of hydraulic conductivity-restricting surface seals that result when aggregates break down, dispersing clay that blocks small pores.
        Greater aggregate stability is also associated with maintenance of surface roughness and resistance to erosion.  While the importance of these phenomena have been demonstrated before for rainfed erosional processes (with splash-related energy, detachment and transport), few if any reports have documented these effects with furrow irrigation-induced erosion, which has no splash component.
         Analysis of the seasonal application pattern of PAM and resulting erosion in this study confirm that most of the season's erosion can be avoided in furrow irrigation with only a few kilograms per hectare of PAM application early in the season applied in sequential irrigation events.