February (No. 493)
Polymer posts gain grower attention
A new polymer trellis post has been launched in Australia. The product, designed by Trellis Systems of Auburn, New South Wales, has two key benefits for grapegrowers – and more broadly – the wine industry: it saves the environment, and it saves on grower production costs.
The polymer post’s environmental benefits are twofold. The posts are manufactured from recycled plastics and products such as printer cartridges, carbon paper and cool-drink bottles, which would otherwise go to landfill. Second, the use of the post provides an alternative to the common copper, chrome and arsenate (CCA)-treated pine posts, which have been prioritised as the number one environmental issue facing the wine industry (Wightwick, 2003).
As vineyards age, the relatively brittle CCA-treated pine posts are susceptible to breakage under machinery impacts. Anecdotal evidence suggests that due to wear and tear or natural decay, the annual replacement rate of posts in a vineyard may be as high as 15%. Within five years, 6 million posts will require disposal annually, equivalent to more than 120,000m3 or approximately twice the annual amount of waste deposited in a landfill catering for a population of 60,000 people (Smith and Mollah, 2004).
The most significant problem associated with the use of CCA-treated posts is the disposal of broken or obsolete trellis posts. Burning of CCA-treated products has been prohibited for a decade in some States, as it has been acknowledged that the smoke produced constitutes an environmental and human health hazard (Smith and Mollah, 2004).
Paul Gold, sales manager for Trellis Systems, said the company set about manufacturing the new polymer post with the clear idea that if it could prevent poisoning the earth through providing an alternative to CCA-treated wooden posts, plus recycle plastics and waste products which would otherwise be dumped, it would be providing a dual benefit to the ecology.
However, Gold said, the post had to offer more than environmental benefit, it also needed to be financially viable and offer real cost savings to the wine industry.
“Without offering cost savings, it would fail,” Gold said.
“This post does not need constant ongoing attention because it is so stable. It will last around 20 years, is UV-stable, and will not corrode. Because of these low-maintenance attributes, we anticipate that savings per hectare over 10 years could reach as high as $22,000.”
Gold said the company had initiated its own comparison of installation and maintenance costs of CCA-treated posts, white cyprus/eucalyptus posts, steel and the Trellis Systems’ polymer post.
“Our personnel observed vineyard workers installing posts in the Mildura area to get a sense of the average time required to install the various types. We also rang supplier companies to find out prices of posts, galvanised staples and other consumables required in each instalment process,” he said.
Through this comparison (see Table 1), Trellis Systems found that although the polymer post cost more to initially install, $15.33 per post compared with steel at $8.07, CCA-treated posts at $10.58 and cyprus/eucalyptus posts at $16.94, the savings in replacement costs per hectare of time due to broken, corroded or bent posts changed the cost comparisons.
The Trellis Systems’ in-house survey, using annual replacement costs based on 5-10% of pine posts breaking at harvest, each one costing $150 to replace (CSIRO, 2001) found that over a 10-year period the net cost per post, per year, became $4.53 for the polymer post, $9.19 for the cyprus/eucalyptus post, $12.81 for the steel post and $16.06 for the CCA-treated post.
While environmental benefits and cost savings were the number one factors when Trellis Systems designed the polymer post, others included:
- capacity to withstand storms, to ensure no risk of collapsed vineyards due to inadequate purchase of the trellis post in the soil
- capacity to add to crop yield, through making mechanised pickers more effective
- not damage harvesting machines in the process
- was easy to install
- would not need constant attention due to rotting, breakage or corrosion of posts.
“The design incorporates a special cross section that has maximum purchase in the soil and increased strength around the stem. It will withstand the vagaries of the weather, and is strong enough to ensure that it will support all known vines,” Gold said.
“We installed 55 posts at the Evans Wineries at Camden, so that we could see how they performed. The posts were driven into the soil by a manual post driver, with no preparation having been done to the earth.
“We had to find out how our posts stood up to harvesters, so we installed three posts in hard earth adjacent to the vineyards. The harvester drove into the first post, snapping it. He did manage to pass over the other two with the rods beating furiously, and there was no damage.
“He then passed over the posts another four times, still no damage. Next time, he parked the harvester on top of the posts for four minutes beating madly, and again, only a few chips on the flanges.
“We asked the viticulturist how many years of service this test had simulated, and his guess was ‘about 40!’”
Gold said further tests were conducted by attaching a rope to the top of the post, and getting 100kilograms of “good Aussie muscle” to pull upon it.
“He had to pull very hard to get significant deflection of the post, and it did not snap. Further, it returned to the straight position every time. We have ensured that the posts have the elasticity to always keep their shape,” he said.
“Special slots and latches are incorporated, so that no additional tools are needed to complete the instalment process.
“The spacing and height of all the wire/irrigation provisions has been made to grower specifications. Installation is easy because there is a special “driver plate” incorporated in the design.
“Because the posts are lighter (3.70kg for the polymer post compared with CCA-treated pine posts at around 25kg) more posts can be carried on a truck, making them more economical to transport,” Gold said.
In early demonstrations, Gold said Australian grapegrowers have shown high interest in the polymer post. Several Hunter Valley growers have also installed blocks or rows of the polymer posts as they conduct their own in-house assessments.
Gold also visited more than 40 wineries in the Margaret River region in January, to show growers and viticulturists the polymer post and said the product was once again extremely well received.
Smith, T., Mahabubur, M. (2004) CCA review – implications for viticulture. The Australian & New Zealand Grapegrower & Winemaker. 483:44-48.
Wightwick, A. (2003) National Wine Industry Waste Management Forum. The Australian & New Zealand Grapegrower & Winemaker. 472:43-45.
CSIRO Onwood (2001) Eucalypt posts for vineyard trellises. Research update from CSIRO Forestry and Forest Products. 33.