Degradable plastic mulch

David McGrath from EconVerte at the NT Farmers Field Day at Red Dirt Melons, Katherine

Top End melon growers would like to use degradable plastic beneath crops instead of the conventional plastic, but as yet, no product has been found suitable for the Top End’s climate.

Plastic mulch is used on row crops to reduce pests, weeds and retain water, soil and nutrients. Stuart Smith from DPI&F estimated that 7,000km of conventional, non-biodegradable plastic mulch was rolled out in the NT in 2012. This is normally burnt or buried each year.

Degradable and bio-degradable plastics are available but expensive and tend to break down too quickly in the Top End, rendering them useless.

David McGrath, founder of EconVerte, is trying to address the gap in technology with a product called Degricover, a degradable plastic mulch film. Degricover has a retarding agent and degradant. The retarding agent keeps the plastic strong so it isn’t split by rocks or birds. The depletion time of the retarding agent is pre-determined to 3, 6, 8 or 10 months. Then the degradant is exposed and the product starts to become brittle and breaks up.

David talked to farmers at a recent Top End field days and said that Degricover is cheaper than other degradable products and only about 3c/m more expensive than conventional plastic, but the cost of removing and disposal is avoided. Also, thinner film could be laid if it doesn’t need to be picked up (strength required).

Degricover breaks down when bonds are exposed to oxygen, not light or water. When it is laid, the stretching process exposes the cells, which starts the clock on the retarding agent. When this agent is depleted, David says the degradation period starts and can’t be stopped, so while buried parts may take longer to degrade, they will degrade. These parts may be ploughed in because they will degrade even if buried.

David said that the oxo-degradable additive in the plastic reduces the Molecular Weight of the plastic sufficiently to enable safe consumption by micro-organisms through to biomass, a natural component of soil. The more microbes in the soil, the more degradant will be taken up.

New products can’t break down too slowly either, otherwise it will need to be removed mechanically like conventional plastic so that cover crops can be sown. David is trying to improve the speed of the degradant period. Meanwhile, some farmers are currently trialling the product.  

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