Waste glass used as grape vine mulch

A Christchurch winery says it is taste-testing the wine made from a block of vines on which it has experimented by laying beds of crushed glass to suppress weeds, retain soil moisture and improve ripening of the grapes.

The pilot project, a world first, is being conducted at Sandihurst Wines by Dr Glen Creasy, of Lincoln University, partly to find new ways to recycle thousands of tonnes of waste glass.

Crushed glass spread underneath the vines reflects sunlight back up onto the fruit to enhance ripening. The glass is the size of coffee sugar crystals and is safe to touch.

The trial started in December 2005 and results so far have shown it improves soil moisture retention, weight of grape clusters and weed suppression in the vineyard, and adds complexity to the wines -- in this case, pinot noir.

Some councils around New Zealand concerned about "glass mountains" of bottles and other glass which are uneconomic for recycling have been grinding down the waste and using it for things such as roading materials.

Other waste glass projects include trials into the use of crushed recovered glass bunkers on golf courses as an alternative to sand.

When the NZ dollar was strong, huge volumes of glass products were imported cheaply, rather than being made domestically, and much of the imported glass was clear "flint" glass that was less suitable to recycle.

Linda Norris, chief executive of the Sustainable Initiatives Fund, said the cost of transporting waste glass to Auckland, or Asia made it even harder for South Island councils.

"Trucking substantial amounts of glass waste to Auckland or shipping to Asia for a marginal return just doesn't make good economic sense," she said.

Every year 13,000 tonnes of waste glass is produced in Christchurch, much of it marginally recyclable.

"Finding a use for all the waste glass collected in Canterbury has been a real problem," said Ms Norris. "We've been looking for other uses that are viable."

Research winemaker Kerrie Stronge, from Hortresearch, is conducting the taste-test.

Dr Creasy said he liked the way using the glass under the vines was coming full circle, in that glass that is used in the wine industry could be crushed and used to improve the wine.

The Sustainable Initiatives Fund backed the Sandihurst project by putting in $25,000 to test the viability of using crushed recovered glass on vineyards.

The winery trial has used just 35 tonnes on a small block, but extending the crushed glass mulch to more wineries in the South Island would use much more. The glass can be crushed in a mobile crusher at the rate of 12 tonnes an hour.