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December 2006

Vineyards apply custom blends of food-scrap compost

In the last 60 days modern compost facilities in California have shipped 7,500 cubic yards (218 truckloads) of finished compost made with food scraps collected from San Francisco and Oakland restaurants to local vineyards.

The compost, made from a diverse feedstock of kitchen trimmings and plate scrapings, returns nutrients to vineyards and farms, stimulates microbial activity and improves soil structure.

Now growers are taking the additional step of having the two Northern California compost facilities blend in extra amendments such as rock phosphate, gypsum, lime and sulfate of potash.

“By applying compost blended with specific amendments that lab tests of vineyard soils show are needed we can tailor the compost to feed vineyards and farms nutrients they more specifically require,” said William Brinton, who operates Woods End Research, a soil and compost-testing lab, and advises growers on compost recipes and soil requirements.

The two compost facilities, Jepson Prairie Organics and South Valley Organics, make Four Course Compost from restaurant food scraps, store additional amendments onsite and mix custom compost blends to vineyard specifications.

Blending rock phosphate into compost, called “rock composting,” is an extra step that most compost operations will not take but is highly beneficial to growers, said soil scientist Bob Shaffer, of Soil Culture Consulting in Glen Ellen, California.

The phosphate comes from a Florida mine. “It is very high in quality, a pure source of phosphate particles,” Shaffer said. Microorganisms and humic and folvic acids in the compost “pre-digest” the phosphate; that action makes the essential mineral more available to plant roots and increases nitrogen retained in the compost, Shaffer said.

Adding phosphate also provides calcium, iron and trace elements. “Plants respond to this very well,” Shaffer said.

Every harvest removes nutrients from the soil. Nutrient-rich compost returns nitrogen, phosphorus, potash and organic matter to the soil, giving growers an alternative to chemical fertilizers.

The finished compost encourages leafy growth and succulence, promotes a strong root system and builds disease resistance. Blending in amendments at the compost facilities also saves growers the time and expense of doing it in the field.

More than 100 vineyards and several organic farms have applied truckloads of the rich soil amendment. Many are rushing to apply the soil amendment before the winter rains begin.

The Organic Material Recovery Institute (OMRI) of Eugene, Oregon has a process to approve specific natural amendments based on review of the ingredients and the composting methods. OMRI has approved Four Course for use on organically certified farms.

More than 2,000 restaurants in the San Francisco area and thousands of city homes provide food scraps to the program. Sunset Scavenger and by Golden Gate Disposal & Recycling, operating companies of Norcal Waste Systems, Inc. collect 330 tons of compostable material a day.

The scraps are transported to Jepson Prairie Organics and South Valley Organics, compost facilities owned and operated by San Francisco-based Norcal. Compost workers screen, grind, compost and cure the material using modern composting equipment and techniques. The end products include Four Course and associated blends of nutrient-rich, finished compost favored by Northern California vineyards and organic farms.

“This is our busiest time of year,” said Robert Reed, spokesman for Jepson Prairie Organics and South Valley Organics. “The growers want to get this compost on their vineyards and fields now because the rain will carry the nutrients into the soil to feed plant roots, and the compost will help soil retain water.”


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