POLYACRYLAMIDE FOR SURFACE IRRIGATION TO INCREASE NUTRIENT-USE EFFICIENCY AND PROTECTWATER QUALITY

Abstract

Furrow irrigation systems have a greater application capacity, are less costly, and use less energy than sprinkler systems but furrow irrigation produces greater runoff, erosion, and deep percolation losses. Phosphorus (P) and nitrogen (N) losses are associated with runoff sediment, and can be minimized by eliminating irrigationinduced erosion. Excessive leaching of inorganic and organic solutes commonly occurs at the inflow region of furrow irrigated fields where infiltration opportunity times are longer. In one conservation practice, a high molecular weight, anionic polyacrylamide (PAM) is applied to advancing furrow stream flows at a concentration of 10 mg L⁻¹. Because PAM stabilizes furrow soil and flocculates suspended sediment, we hypothesized that this treatment would reduce runoff losses of sediment, molybdate reactive P (MRP), total P, NO₃-N, and chemical oxygen demand (COD). Polyacrylamide treatment may increase furrow infiltration in some soils. However, we hypothesized that because it permits higher initial inflows, PAM would not increase NO₃-N or Cl leaching relative to conventional, constant inflow irrigation. To test the first hypothesis, all treatments had the same inflow regime. For hypothesis two, control inflows were a constant 15 L min⁻¹; PAM treated in- flows were cut back from 45 to 15 L min⁻¹ after furrow advance. Irrigation runoff and percolation waters were sampled and analyzed. Polyacrylamide increased infiltration and decreased runoff, particularly early in the irrigations. Mean cumulative runoff sediment loss over 12 h was 11.86 kg for each control furrow vs 1.15 kg for PAM-treated furrows. The PAM reduced 12-h cumulative sediment losses in runoff by 90%, MRP by 87%, total P by 92%, and COD by 85%, relative to control furrows. Polyacrylamide had no field-wide, season-long effect on cumulative amounts of water, NO₃-N or Cl leached. The PAM-technology effectively prevented soil nutrient losses, increased nutrient-use efficiency, and decreased N and P loads in irrigation return flows and receiving surface waters.

ACKNOWLEDGMENT

This work was supported in part by a grant from CYTEC Industries, through a Cooperative Research and Development Agreement (contract 58-3K95-4-216). Comments by Drs. Mahdi Al-Kaisi, Jan Boll, and Robert Mahler on an early draft of the manuscript were greatly appreciated. We thank Dr. Anita Koehn, Mr. Ron Peckenpaugh, Mr. Jim Foerster, and Mr. Andrew Mutziger for their valuable technical assistance, and Ms. KristenSwafford, Ms. JamieWard, Ms.RiquiHeinemann, and Mr. Seth Oliver for their help in the lab and field.