Sprinkler Irrigation Runoff and Erosion Control with Polyacrylamide — Laboratory Tests

Many semiarid and arid soils are prone to irrigation-induced erosion. Polyacrylamide (PAM) greatly reduces erosion from furrow irrigation. We hypothesized that PAM applied via sprinklers will provide erosion control and benefit water infiltration and aggregate stability. Screened (6.4 mm) Rad silt loam (coarse silty, mixed, superactive mesic Durinodic Xeric Haplocambid) was placed in 1.5 by 1.2 by 0.2 m steel boxes with 2.4% slope. An oscillating nozzle, 3 m above the soil, produced a median drop size of 1.2 mm diameter. We applied 0, 1, 2, 4, and 6 kg ha' PAM in 20 mm of water in the first irrigation, followed by two 20-mm water-only irrigations. In a second test, we applied 0, 2, and 4 kg ha ' PAM in 8 mm of water in the first irrigation, followed by two 20-mm water-only irrigations. Two kilograms per hectare PAM in the first 20-mm irrigation reduced runoff 70% and soil loss 75% compared to control. Polyacrylamide in 8 mm of water was less effective. Polyacrylamide in the 20-mm irrigation did not affect tension infiltration; PAM in the 8-mm irrigation doubled tension infiltration following the third irrigation. Wet aggregate stability following the first irrigation was greater in all PAM treatments than on the check. With 2 kg ha" PAM in the 20-mm irrigation, it was 55%; in 8 mm, 77%. Polyacrylamide applied in the first irrigation at low rates effectively reduced runoff and erosion. Erosion was more effectively controlled than runoff. I RRIGATION predominates agriculture in semiarid and arid climates. About 240 million ha (15-17%) of the world's cultivated lands are irrigated and about onethird of the world's food production is grown on about 50 million irrigated ha (Hoffman et al., 1990; Gleick, 1993; Tribe, 1994). Total irrigated land in the USA was 24 684 055 ha in 1996, a 2.8% increase from 1987. From 1987 to 1996, the percentage of sprinkler-irrigated acreage increased from about 40 to about 44% (Anonymous, 1997). Most semiarid and arid soils supporting irrigated agriculture have thin, erodible surface soil horizons. Therefore they are prone to irrigation-induced erosion and rapid productivity loss if not well managed (Carter, 1993). Conservation practices such as residue management and reduced tillage have not been readily adopted in surface irrigated agriculture. Such practices are considered by some to interfere with water flow and sometimes with planting and harvesting operations because of excessive residue. Also, following crops such as potato (Solanum tuberosum L.), dry bean (Phaseolus vulgaris L.), and sugar beet (Beta vulgaris L. subsp. vulgaris), very little residue is available to protect the soil surface from erosion. Under such conditions, application of about 1 kg ha1 USDA-ARS Northwest Irrigation and Soils Res. Lab., 3793 N. 3600 E., Kimberly, ID 83341. Received 18 Dec. 1997. *Corresponding author ([email protected] ). Published in Soil Sci. Soc. Am. J. 62:1681-1687 (1998). of the high molecular weight anionic long-chain organic polymer, PAM, with an 18% negative charge density, in the irrigation furrow advance water has been demonstrated to reduce furrow erosion by as much as 99% (e.g., Lentz et al., 1992; Lentz and Sojka, 1994; Trout et al., 1995; Sojka and Lentz, 1997). The practice has been researched and documented and has become widespread and popular enough for the USDA-NRCS to publish an interim conservation practice standard for the use of PAM in furrow irrigation (USDA-NRCS, 1995). Less studied is the efficacy of PAM when mixed with irrigation sprinkler water or injected directly into overhead sprinkler systems. Shainberg et al. (1990) applied three rates of PAM on dry soil in a small-tray laboratory study prior to sprinkling with a rainfall simulator. They found that 20 kg ha1 PAM was most beneficial in maintaining high infiltration rates. Smith et al. (1990) and Levin et al. (1991) in similar studies found that 20 kg ha 1 of PAM increased infiltration and greatly reduced runoff and erosion. Ben-Hur et al. (1989) concluded from a small-tray laboratory study that applying 5 kg ha1 PAM with simulated irrigation water was more effective in maintaining high infiltration rates than was spraying the polymer on the dry soil surface prior to simulated irrigation. Levy et al. (1992) found that applying PAM at 10 mg L1 to irrigation water in a small-tray lab study gave optimal effect on final infiltration rate and cumulative infiltration as well as on reducing erosion. In a field plot study, Flanagan et al. (1997a,b) found increased water infiltration and attributed this to reduced surface sealing when they applied 10 mg L1 of PAM to tap water used in simulated rainfall on wet runs. Sediment concentration was greater in runoff from PAM-treated soil than from untreated soil, but it was not clear if PAM reduced or increased sediment loss. Surface sealing and soil crusting have been controlled and runoff and erosion significantly reduced in field plot studies by spraying PAM on dry soil surfaces prior to sprinkler irrigation (Levy et al., 1991; Ben-Hur, 1994; Zhang and Miller, 1996). Stern et al. (1992) sprayed a dry soil surface with 20 kg ha1 PAM prior to sprinkler irrigation. They found significantly greater wheat (Triticum aestivum L.) yields on plots where PAM had been applied as compared with the control. They attributed the greater yields to better soil water distribution and increased irrigation water use efficiency. Runoff and erosion increase with increasing water drop energy. However, PAM limits physical disintegration of aggregates caused by water drop impact. Smith Abbreviations: EC, electrical conductivity; PAM, polyacrylamide; SAR, Na adsorption ratio.