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ARS Home » Pacific West Area » Kimberly, Idaho » Northwest Irrigation and Soils Research » Research » Publications at this Location » Publication #78391

Title: REDUCING PHOSPHORUS LOSSES FROM SURFACE-IRRIGATED FIELDS: EMERGING POLYACRYLAMIDE TECHNOLOGY

Author
item Lentz, Rodrick
item Sojka, Robert
item Robbins, Charles

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Runoff from furrow irrigated fields contains sediment, phosphorus, and other nutrients that enter surface waters as non-point source pollutants. Current practices that reduce furrow irrigation soil loss are effective but not widely accepted by farmers. An emerging new practice that applies an anionic polyacrylamide (PAM), a long-chained polymer, reduced sediment losses in irrigation runoff by up to 97%. We wanted to determine whether PAM treatments would also reduce runoff concentrations and field losses of phosphorus, and other pollutants. Control furrow streams contained no PAM. PAM was applied continuously at 1 ppm in the continuous PAM-C1treatment, and was applied at 10 ppm only when water first ran down the dry furrow, in the standard PAM-I10 treatment. Total seasonal soil loss was 3.14 Mg/ha for control furrows, 0.35 for PAM-C1, and 0.25 for the PAM-I10 treatments. Relative to controls, the best performing PAM-I10 reduced total furrow losses of sediment by 92%, total-P by 91%, ortho-P by 86%, and lowered COD by 83%, but had little influence on runoff nitrate. PAM-treatments drastically reduced nutrient and organic losses from the fields. Thus, this practice could greatly reduce non-point source phosphorus pollution from agricultural lands, and prevent the loss of expensive fertilizers that are applied to fields by farmers to enhance productivity. PAM technology is economical, costing about $5 per acre per irrigation, and is enthusiastically accepted by many farm managers in the irrigated West.

Technical Abstract: Most phosphorus (P) losses from surface-irrigated fields can be minimized by eliminating irrigation-induced erosion. Furrow irrigation produces more erosion than other surface irrigation systems. Farmers hesitate to employ known effective practices because they are inconvenient, invasive, or uneconomical. A convenient new practice uses a high molecular weight, anionic polyacrylamide (PAM) applied to irrigation inflows. We hypothesized that, compared to control furrows, PAM treatment would reduce field losses of ortho P, total P, nitrate, and lower tailwater chemical oxygen demand (COD). Two PAM treatments were tested: I10 applied 10 mg/L PAM only during the furrow advance phase (until runoff began) , and C1 applied 1 mg/L PAM throughout the irrigation. Soil was Portneuf silt loam (Durixerollic Calciorthid) with 1.6% slope. Initial 23 L/min inflows were cut back to 15 after 1.5-6 h. Total soil loss over four irrigations was 3.06 Mg/ha for control furrows vs 0.33 (C1) and 0.24 (I10) for PAM-treated furrows. Relative to controls, the best performing PAM-I10 treatment reduced total furrow losses of sediment by 92%, total-P by 91%, ortho-P by 86%, and lowered COD by 83%, but had little influence on runoff nitrate. PAM-I10 lowered furrow stream nutrient concentrations more than did PAM-C1, but owing to disparities in runoff, the two treatments produced similar total sediment and nutrient losses. PAM is effective, convenient, and economical, and greatly reduces phosphorus and organic losses from surface irrigated fields.