Green trash reduces herbicide run-off

Author/Source: cane grower

02/04/2010

The move to minimum till farming and green trash blanketing has led to the significant reduction in sediment movement across cane growing regions. Such is the success of the practice that sediment movement from sugarcane is no longer considered a major priority compared to other water quality concerns.

The strategy behind minimum till is the increased reliance on herbicides to manage weeds, where once this was achieved through cultivation.

 

When it comes to herbicides, there is a strong perception that agricultural run-off containing herbicides from sugarcane are detrimental to the Great Barrier Reef and its resilience to the impacts of climate change.

 

Is the increased prevalence of herbicide being recorded in the reef and its catchments a perverse outcome of improved practice adopted to combat another problem? Or aren’t we aware of the benefits of a green trash blanket’s affect on reducing the movement of herbicides?

 

Science by Australian and US researchers (a list of references is available) on green cane trash blankets (GCTB) in sugarcane production and its effects on herbicides indicate that GCTB has a positive mitigation effect on the movement of herbicides.

 

The theory behind GCTB positive influence on herbicide movement is due to it changing the properties of the chemistry and microclimate of soil, therefore affecting volatilization, degradation and uptake of herbicides.

 

Research also points to the organic matter fraction having significant impact on the sorption of organic chemicals.

 

Some key points

·        Extractable concentrations of atrazine were at least one order of magnitude higher for the sugarcane mulch residue compared with that retained by a sit loam soil in Louisiana.

·        Atrazine retained by the crop residue is subject to dissipation or adsorption processes, thus reducing the amount available for run-off and movement into the soil by the first rain.

·        A minimum of 50% reduction in run-off effluent concentrations for atrazine was realized when the sugarcane mulch residue was not removed.

·        GCTB can hold the herbicide in the field longer and may also promote microbial activity. This microbial activity can be further enhanced through temperature from the GCTB as herbicides are more susceptible to degradation at higher temperatures.

·        Soil organic carbon influences the magnitude of atrazine sorption and photodegradation in the soil surface is accelerated as the percentage of organic matter increases.

·        pH influences the fate of herbicides in the environment and the addition of a GCTB to the soil surface can create a change in pH in the surface soil layer.

 

Considering sugarcane residue provides more than 90% groundcover at masses greater than 2.68 tonnes per hectare in Queensland, the use of GCTB can have a considerable impact on the movement and fate of herbicides.