Hitting the marc

Wines & Vines, August, 2001 by Frank Smith

Marc, the waste material after juice has been extracted from grapes, is becoming a major disposal problem worldwide, especially for larger wineries with small areas available for land disposal.

But Australian organic recycling operator Bill Gifford reckons marc is a potentially valuable asset.

"I think wineries will find they are sitting on a valuable resource," he says.

Gifford set up a composting program to provide an alternative to landfill disposal for green urban waste such as prunings, leaves and lawn clipping, in 1994.

At first these products were sold to the landscaping and home garden industry, but they are now in demand as a mulch in vineyards, and marc is showing its value as a compost component.

"You get a very open compost when marc is incorporated," Gifford says.

He says wineries can make compost simply by heaping chopped green residue in windrows and monitoring the inside temperature, turning the compost with a fore-end loader when it reaches 60[degrees] to 70[degrees]C. He recommends a second treatment in a tub grinder fitted with a smaller sieve and a second composting to ensure all weeds and pathogens are killed.

Cape Mentelle vineyard in Western Australia has used a similar composting system for eight years. Viticulturist Brenton Air makes compost on the property by incorporating marc, poultry manure and locally available wood waste. The compost reaches 60[degrees] to 65[degrees]C and takes four to five months to mature.

Air says he turns the compost when the [CO.sub.2] level appears too high.

Trials by scientist John Buckerfield in South Australia showed a reduction in water needs, increase in soil organic matter and a likely reduction in fertilizer and herbicide use when compost is applied to grape vines. In the trials, a 50mm deep mulch of compost was applied to a vineyard prior to planting.

After six months, shoot length and shoot diameter were 50% larger than in the control vineyard. At 18 months, yield was substantially higher as were number of bunches per vine, compared to the control.

"No mulched vines were under stress," Gifford says. "Soil temperature and moisture were consistent and earthworm numbers peaked at 200/[m.sup.2] under 25 to 50mm compost compared to 40/[m.sup.2] for the controls."

Raw marc at Evans and Tate's Western Australian vineyard proved too acidic to apply direct to the vines. However, after composting for a year and blending with 50/50 chicken manure the compost has a near-neutral pH of 7.3 and useful contents of nitrogen and trace elements.

Gifford says as little as 25mm of compost improved the yield of table grapes on one property by 18%, with better water penetration and less resistance to a penetrometer, while another local property reported 18 berries per kg on mulched vines compared to 24/kg on the control. Berry size, especially for the Chinese New Year market, is very important in table grapes. This property also reported a 20% decrease in irrigation water use and 25% savings in fertilizer.

While trials are continuing, Gifford is confident that compost mulching, with the addition of marc, will improve yields and reduce irrigation needs, as well as dispose of an unwanted byproduct of winemaking.

(Frank Smith lives in Perth, Western Australia. He specializes in corporate and science writing.

Effect of Mulching Winegrape Vines with
Compost
                             MULCHED
                        WITH COMPOST  CONTROL
Shoot length                   125mm     75mm
Shoot diameter                  14mm     10mm
Yield at first harvest         2.5kg   0.75kg
Bunches/vine                      43       21
Raw and Composted Marc Composition
               RAW     COMPOSTED
               MARC      MARC
Nitrogen     1.4-1.6%    2.3%
Potassium    2.1-2.3%    1.3%
Phosphorous  2.0-2.4%    0.5%
pH           3.7-3.9%    7.3%