Herbicides wash off from cane trash by rainfall

Dang, Aaditi (2012) Herbicides wash off from cane trash by rainfall. [USQ Project]

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Abstract

Over the past 150 years, coral reefs around the world have been extensively modified for agricultural production and urban settlement leading to a decline in water quality. This includes the water entering the Great Barrier Reef (GBR) lagoon of Australia. A scientific consensus statement on water quality in the GBR has concluded, ‘water discharged from rivers to the GBR continues to be of poor water quality’, and ‘land derived contaminants, including suspended sediments, nutrients and pesticides, are present at concentrations to cause environmental harm. This led to development of the Reef Rescue and Reef Plan programs in 2009.

Rainfall runoff of herbicides routinely used in sugarcane production has potential to cause harm to rivers, lagoons, and the GBR in Northern Australia. The fate of these herbicides can be modeled within the landscape to assist in identifying efficient strategies to reduce herbicide runoff and develop better land management practices. Little data is available on the mobility and concentrations of herbicides leaving surface trash cover during rainfall events by the process of washoff.

The purpose of this laboratory study was to quantify the amount of herbicides washing off sugar cane trash during simulated rainfall, to provide insight into herbicide behavior in the field.

Simulated rainfall was used to apply 100 mm of rain at a constant intensity of 50 mm/h on plots covered in cane trash. As an initial benchmark study, trash was sprayed with a conservative tracer, potassium bromide (KBr). The KBr results show that the concentrations of bromide washing off were initially very high, and declining exponentially as a function of time. However after about 5 minutes the wash off approaches a steady rate.

A similar procedure was used for the herbicide trials. Herbicides tested were ametryn, atrazine, tebuthiuron, S-metolachlor, diuron and hexazinone. The effect of ‘time after spraying’ on concentration in wash off was also investigated through a series of experiments where plots were sprayed and left for varying time durations of 24 hours, 8 days and 40 days before being rained on.

The herbicide washed off showed a sharp decline in wash off concentrations for all the tested herbicides at 5 minutes, followed by steady decline similar to KBr wash off. Each herbicide had differing coefficients of wash off due to different sorption coefficients and different decay rates. Wash off parameters used in herbicide runoff model were fitted to the data and compared.

This study will provide insight into the exact nature of the wash off from cane trash and provide wash off parameters for herbicide modeling. This will provide information on the safe application of herbicides and efficient strategies that can be employed to reduce the herbicides wash off to GBR the water bodies.


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Item Type: USQ Project
Refereed: No
Item Status: Live Archive
Faculty / Department / School: Historic - Faculty of Engineering and Surveying - Department of Agricultural, Civil and Environmental Engineering
Supervisors: Craig, Ian; Silburn, Mark
Date Deposited: 20 Feb 2013 06:08
Last Modified: 20 Feb 2013 06:08
Uncontrolled Keywords: herbicide wash off; sugar cane trash; herbicide modeling
Fields of Research : 09 Engineering > 0907 Environmental Engineering > 090703 Environmental Technologies
URI: http://eprints.usq.edu.au/id/eprint/23038

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