(A brief, pre-publication summary of Sojka, R.E. and Lentz, R.D. and Westermann, D.T. (1998) Water and erosion management with multiple applications of polyacrylamide in furrow irrigation. Soil Science Society of America Journal. 62:1672-1680.)

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 ^-3PAM in advancing 23 L min ^-1furrow streams (reduced to 19 L min ^-1after 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 ^-1inflows (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

Figures

	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.
	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.
	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.
	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.

Tables

Table 1Total 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).

Table 2Statistics 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.

†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.

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

†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.

†Standard deviation is shown as (n).

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

†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.

†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.

†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.