Minimising off-site movement of contaminants in furrow irrigation using polyacrylamide (PAM). I. Pesticides

Abstract

Off-site movement of pesticides from furrow-irrigated agriculture has been a concern in the Ord River Irrigation Area, Western Australia. After consultation with growers a range of management strategies were tested to assess the effectiveness of various practices to minimise off-site movement of pesticides during irrigation. This paper reports on the effectiveness of the additions of high molecular weight, anionic, polyacrylamide (PAM) to irrigation water to minimise off-site movement of endosulfan, chlorothalonil, bupirimate, and atrazine. Water leaving from 4 separate irrigation bays, which consisted of 25 furrows per irrigation bay (Expt 1) or 39 furrows per irrigation bay (Expt 2), was monitored over time. The average concentration of endosulfan α and β and bupirimate leaving the irrigation bays for the duration of the single irrigation event was generally always less for the PAM-treated irrigation bays than the control (control treatment). The addition of PAM to the irrigation water significantly decreased the cumulative runoff losses (g) of total endosulfan by 54% from 11.41 to 5.19 g/ha (P < 0.05), and of chlorothalonil by 49% from 53.65 to 27.32 g/ha (P < 0.001). There was no statistical difference in the load of atrazine or bupirimate leaving either treatment. Although the addition of PAM to irrigation water effectively decreased the off-site movement of 2 fairly strongly sorbed pesticides, endosulfan and chlorothalonil, it did not decrease the total load moving off-site of the more weakly sorbed pesticides, bupirimate and atrazine. The addition of PAM as a liquid to irrigation water was not found to increase the infiltration of a soluble pesticide, atrazine, into the soil profile. The mode of application of PAM, however, may affect water infiltration and hence vertical movement of soluble pesticides and requires further investigation.