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

Most P losses from surface-irrigated fields occur via runoff, are asso ciated with eroded sediment, and can be minimized by eliminating irrig ation-induced erosion. A convenient new practice that eliminates furro w irrigation-induced soil losses uses a high molecular weight, anionic polyacrylamide (PAM) applied to initial irrigation inflows. We hypoth esized that, compared to control furrows, PAM treatment would reduce f ield losses of ortho P, total P, NO3 and lower tailwater chemical oxyg en demand (GOD), Two PAR I treatments were tested: lie applied 10 mg L -1 PAM only during the furrow advance (i.e., the application was halte d after runoff began) and C-1 applied 1 mg L-1 PAR I continuously thro ughout the irrigation. Soil was Portneuf silt learn (coarse-silty, mix ed, mesic Durixerollic Calciorthid) with 1.6% slope. Initial inflows w ere cut bark from 23 to 15 L min(-1) after 1.5 to 6 h. Total soil loss over four irrigations,vas 3.06 Mg ha(-1) for control furrows vs. 0.33 (C-1) and 0.24 (I-10) for PAM-treated furrows. Ortho-P and total P co ncentrations in control tailwaters were five to seven times that of PA M treatments, and COD levels were four times those of PAM treatments. Runoff in controls was two times that of PAM-treated furrows. PAM-I-10 lowered furrow stream nutrient concentrations more than did PAM-C-1, but owing to disparities in runoff, the two treatments produced simila r cumulative sediment and nutrient mass losses, The PAM is effective, convenient, and economical, and greatly reduces P and organic material (GOD) losses from surface-irrigated fields.