On-farm management practices to minimise off-site movement of pesticides from furrow irrigation.

Off-site movement of pesticides from furrow-irrigated agriculture has been a concern in the Ord River Irrigation Area, Western Australia. This paper reports on the effectiveness of incorporation of pesticides by cultivator or power harrows before irrigating, and spraying pesticides only onto beds to minimise off-site transport. Incorporation of pesticides by power harrows prior to irrigation was found to be more effective in decreasing the off-site transport of a more strongly sorbed pesticide, endosulfan. The average load of total endosulfan (alpha + beta + sulfate) decreased by 74% (P < 0.01) from 11.41 g ha(-1) from the conventionally treated bays to 2.96 g ha(-1) from the incorporated irrigation bays. The total average load of atrazine leaving the irrigation bays was decreased by 81% (P < 0.05) from 87.82 g ha(-1) under the conventional practice of spraying the whole field to 16.95 g ha(-1) by spraying the beds only. A reduction of 52% in total average load of metolachlor was observed following incorporation with power harrows, but this was not significant. Incorporation by cultivator or by power harrows decreased the total load of atrazine or metolachlor leaving the irrigation bays over the whole irrigation period, but these treatments were not shown to be statistically significant, which may have been due to the limited number of field replicates. Incorporation of strongly sorbed pesticides (e.g. endosulfan) prior to irrigation significantly decreased the off-site transport of these pesticides in a furrow irrigation system and may be a useful practice to minimise off-site transport of other similar pesticides. Minimising off-site transport of weakly sorbed pesticides (e.g. atrazine and metolachlor) from a furrow irrigation system is more difficult. The nature of furrow irrigation makes it highly conducive to pesticide transport, particularly of weakly sorbed pesticides, and further work is needed to develop strategies to minimise the movement of this group of pesticides to water bodies.