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Reducing Phosphorus Losses from Surface-Irrigated Fields: Emerging Polyacrylamide Technology

U.S. Dep. of Agriculture, Agricultural Research Service, Northwest Irrigation and Soils Research Laboratory, 3793 N 3600 E, Kimberly, ID 83341.

^* Corresponding author (lentz{at}kimberly.ars.pn.usbr.gov).

ABSTRACT

Most P losses from surface-irrigated fields occur via runoff, are associated with eroded sediment, and can be minimized by eliminating irrigation-induced erosion. A convenient new practice that eliminates furrow irrigation-induced soil losses uses a high molecular weight, anionic polyacrylamide (PAM) applied to initial irrigation inflows. We hypothesized that, compared to control furrows, PAM treatment would reduce field losses of ortho P, total P, NO₃, and lower tailwater chemical oxygen demand (COD). Two PAM treatments were tested: I₁₀ applied 10 mg L^–1 PAM only during the furrow advance (i.e., the application was halted after runoff began) and C₁ applied 1 mg L^–1 PAM continuously throughout the irrigation. Soil was Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic Calciorthid) with 1.6% slope. Initial inflows were cut back from 23 to 15 L min^–1 after 1.5 to 6 h. Total soil loss over four irrigations was 3.06 Mg ha^–1 for control furrows vs. 0.33 (C₁) and 0.24 (I₁₀) for PAM-treated furrows. Ortho-P and total P concentrations in control tailwaters were five to seven times that of PAM treatments, and COD levels were four times those of PAM treatments. Runoff in controls was two times that of PAM-treated furrows. PAM-I₁₀ lowered furrow stream nutrient concentrations more than did PAM-C₁, but owing to disparities in runoff, the two treatments produced similar cumulative sediment and nutrient mass losses. The PAM is effective, convenient, and economical, and greatly reduces P and organic material (COD) losses from surface-irrigated fields.