Composting Grape Pomace in the Finger Lakes

This article was reviewed by the editor of The Tender Fruit Grape Vine for technical accuracy and appropriateness.

The Finger Lakes Grape Program, in cooperation with Matt Doyle (Vineyard Manager for Centerra Wine), hosted a Coffee Pot Meeting on 20 July 2006 detailing the practice of composting, specifically as it relates to viticulture. Participants met at Centerra's pomace compost piles on Middle Road between the towns of Hammondsport and Pulteney. Jean Bonhotal, Cornell Waste Management Institute, presented an overview of the composting process with insights for the grape growing community.

Highlights of the presentation included:

• Start small and experiment with the process before trying it out on a large scale.

• Higher quality compost is produced when there are a variety of feedstocks in your compost pile (i.e. instead of composting only pomace, mix in animal manures or other feedstocks to diversify the piles).

• It is much easier to mix in other feedstocks when piles are first laid down rather than trying to mix them in at a later date.

• Applying a layer of bulking material (e.g. wood chips) under the piles promotes aeration and a more rapid and complete composting process.

• With proper management, pomace-based compost can be finished in 4-6 months.

• Compost should be thought of as a soil health enhancer, not necessarily as a direct fertilizer. Its effect is seen most in improved water retention, cation exchange capacity (CEC = the soil's ability to supply nutrients), soil structure and organic matter content.

• A potential problem with pomace-only compost is its high K+ content which interferes with Mg2+ availability. Vines have not been symptomatic of Mg2+ deficiency, but petiole tests have shown low levels where pomace-only compost has been applied.

• The Cornell Waste Management Institute has published a series of fact sheets on composting. For these and other compostrelated materials, visit their web site.

• Specific questions can be directed to Jean at jb29@cornell.edu

In addition to Jean Bonhotal's discussion, Matt Doyle and Jamie Hawk (Sustainable Viticulture Community Educator) described their respective fertilization/compost field experiments. Centerra Wine is experimenting with nitrogen fertilization in their Elvira vineyards just north of Heron Hill Winery. They have created the following treatments in separate blocks with clay and gravel soils: no additions; compost at 10 tons/acre; inorganic N (ammonium nitrate) at 50 lbs actual/acre; and a combined 6 tons compost and 25 lbs actual N/acre. Matt noted that they are in the early stages of a planned three year trial, so no conclusions can yet be drawn.

Within the Centerra blocks, Jamie Hawk has setup 4 rows of replicates of 6 treatments in both the clay soil and gravel soil sites. The 6 treatments are: no additions; compost at 6 tons/acre; compost at 12 tons/acre; inorganic N (ammonium nitrate) at 25 lbs actual/acre; inorganic N at 50 lbs actual/ acre; and a combined 6 tons compost and 25 lbs actual N/acre. All applications were banded under the rows, and sampling began in mid-May and has been done every 1-2 weeks since. The dual purpose of the work is to 1) describe the soil nitrogen dynamics in the various treatments and sites, and 2) evaluate the Cardy Nitrate Meter for use by growers to obtain a rapid and accurate estimate of available nitrate in vineyard soils. Preliminary results have shown no surprises. Spikes in available nitrate coincided with inorganic additions, soil nitrate levels fell faster in the high leaching potential gravel soils, nitrate levels began to rise prior to N additions as soils warmed and microbial activity increased accordingly, and though the compost additions showed no immediate effect on nitrate levels, anecdotal evidence saw better water retention and soil structure beneath the compost additions.

Notes on Composting Grape Pomace In Virginia

Fritz Westover, Viticulture Research-Extension Associate westover@vt.edu

Wine producers in the state of Virginia have shown increasing interest in producing compost from wine grape pomace, which can then be applied to vineyard soils as a nutrient rich soil conditioner. The notes below have been compiled to provide a quick reference guide for farm wineries initiating small or large scale composting operations.

• pomace is high in N>K>Ca [N-P-K-Ca = 2.0-0.5-2.0-2.0]

• pomace is about 8% seeds, 10% stems, 25% skins, 57% pulp

• in general 1 ton of harvested grapes produces 100lbs of stems and 160 to 240 lbs of pomace (more simply, 3 tons grapes is about equal to 1 ton of total pomace) returns ½ to 1/3 of nutrients and OM removed from crop

• 1:1 ratio, pomace:manure bedding (straw + manure) provides 2/3 to 100% annual nutrient needs of vineyard

• pomace alone composts' slowly - low pH (3.5 to 3.8)

• compost microbes prefer a pH of 6.2 to become active (pH >6 desired)

• lime or other feedstocks must be added to the pomace in order to increase pH

• pomace has C:N ratio appropriate for composting (1:17 to 1:30)

• feedstock added to pomace should also have C:N ratio appropriate for composting (1:20 to 1:30)

• high lignin in seeds (17to 35%) limits decomposition in unturned piles

• wet piles (>60% moisture) may continue to ferment, produce acetic acid = poor quality (check for off odors in pile or other clues of anaerobic activity)

• 1-5 tons per acre annually is considered maintenance application

• frequent turning of pile (2x's or more/week) reduces N & OM

• turning pile only once every 2 weeks retains more N & OM

• pile temperature of 130-140oF for 1 to 2 weeks is necessary to kill weed seeds and pathogens

• pile temperature of 110-140oF is typical after the initial 1 to 2 weeks

• minimum of 3 turns of a pile is also required to kill seeds and pathogens

• keep pile temperature under 160 oF to reduce risk of combustion and loss of beneficial organisms

• composting is a 6 to 10 month process, dependent upon turning frequency, moisture, and temperature of piles or windrows

Related Links

• Cornell Waste Management Institute

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