Polyacrylamide(PAM) - A Method to Control Irrigation Induced Soil Erosion

Reporting Year: July 1, 1998 - March 31, 1999

Personnel: C. Dean Yonts, Irrigation Engineer, University of Nebraska Panhandle Research and Extension Center, Scottsbluff, Nebraska 69361

Objective: Evaluate polyacrylamide for reducing soil erosion in furrow irrigation. Specific objectives include:

1. Measure soil loss in a furrow with and without polyacrylamide in the water.
2. Measure irrigation performance with and without polyacrylamide in the water.
3. Determine the influence of polyacrylamide on water movement within a field.

Background:

Erosion of our top soil has long been a concern but continues to occur as demonstrated by concrete head ditches now located high above the existing field levels. For furrow irrigators the solution to this problem has been difficult because the inherent process of moving water across the soil surface causes soil particles to move with the water. Polyacrylamide has the potential for substantially reducing soil losses during furrow irrigation.

Polyacrylamide increases the stability of soil particles and binds together suspended sediment which reduces the potential of sediments being transported down the furrow. Studies conducted in Idaho suggest furrow erosion can be reduced there by 85 - 99%. Top soil that is lost during furrow irrigation is difficult if not impossible to replace. Cost-effective maintenance of top soil is necessary for long term production of erosive soils.

Another problem in furrow irrigation is the breakdown and silting in of furrows. This is especially true for crops late in the season. As soil is eroded at the upper end of the field, it is depoisted at the lower end. The result of furrow breakdown is the inability to move water to the end of the field efficiently. This is of particular concern with dry beans because of a shallow root system. Soils can often be eroded to depths that are near to the normal rooting depth of dry beans. Polyacrylamide, because of its ability to bind soil particles, can help to maintain the original structure and shape of the furrow.

In addition to the soil binding properties, the use of polyacrylamide has been shown to increase infiltration of water into the soil. As a result, irrigation practices must be studied and adapted to the higher infiltration conditions to obtain the desired irrigation efficiency.

Procedure:

The polyacrylamide field study was conducted at the University of Nebraska, Panhandle Research and Extension Center during the 1998 growing season. Crop grown was dry beans but was not dependent on the results of this test. Field length was 1000 ft. and row spacing was 30 in. Every other furrow was irrigated. Field slope was approximately 0.4.

The experimental design was a randomized complete block with four replications. The irrigation source was canal water. The treatments included:
1) No PAM, conventional irrigation
2) PAM, conventional irrigation
3) No PAM, surge irrigation
4) PAM, surge irrigation

Polyacrylamide was added to the water and furrows during the first irrigation. Furrow flow rate was 15 g.p.m. and remained constant throughout the irrigation event. Furrows selected had the same tractor traffic throughout the entire season. Advance time to the end of the furrow and sediment concentration was measured for each furrow. A total of twelve water samples were collected from each treatment during irrigation to determine total sediment runoff.

Results:

Figure 1 and 2 show the results for sediment loss and furrow advance time, respectively. A significant difference in sediment loss was detected and is given in Figure 1. Using PAM reduced total sediment loss by a factor of more than five times for both continuous and surge irrigation. There was no significant difference in sediment loss between the two irrigation treatments. Furrow advance times are given in Figure 2. No significant difference in furrow advance time could be detected among the four furrow irrigation treatments tested.

In this test, PAM reduced sediment loss for both conventional and surge irrigation systems. PAM did not influence furrow advance time performance of surge irrigation. However surge irrigation did show a trend of shorter advance times when compared to conventional irrigation. Average reduction in furrow advance time has been determined to be approximately 20% when comparing surge to conventional irrigation. The results of this test will be used to initiate a more extensive study to test the differences between surge and conventional irrigation with the use of polyacrylamide.