Grape marc, the by-product of pressing grapes, can be dealt with easily in small quantities. With large acreages, Marlborough wineries are increasingly finding disposal of this substance problematic. Strict Council rules about disposal and storage further complicate the issue. Utilising grape marc as a soil conditioner is an option, but without additional material this substance can damage soil, vine and grape health. In this article, Simon Kemp, Wholesale Landscapes’ Horticultural Specialist, provides advice on optimising the use of grape marc in vineyards.
Studies show the use of raw grape marc as fertiliser on soils can cause an increase in nitrogen leaching and oxygen depletion due to its chemical makeup. Grape marc that has not been composted is high in potassium, which can negatively affect vine health and grape quality resulting in microbial spoilage, premature aging and poor colour in wine. It is important, also, to neutralise pH and optimise the carbon to nitrogen ratio, thereby facilitating nutrient availability. Kemp says Marlborough’s sauvignon blanc produces particularly acidic grape marc which needs to be moderated by the inclusion of a carbon additive.
Should you choose to take a sustainable approach to waste management in your vineyard and utilise grape marc by applying it to your soil, what should you add to optimise its value and keep your soil and vines healthy? Kemp advises that Wholesale Landscapes’ trials over the last three years have shown great results from the addition of Grape Marc Mix.
GRAPE MARC MIX
Wholesale Landscapes’ sampling, undertaken seven months after the Grape Marc Mix was applied, when analysed, showed moderation of the acidity and trace elements in the grape marc. The increased carbon content from the added bark balanced excess nitrogen and provided energy for microbial activity, promoting further break-down. The overall outcome was the production of a highly-effective soil conditioner.
According to Marlborough District Council records, in 2018, an estimated 46,000 tonnes of grape marc was produced by Marlborough wineries, (up from an estimated 45,400 tonnes in 2017). If not stored correctly nitrate, sodium and chloride can leach out of grape marc into surface or groundwater, causing pollution and foul odours. It can also attract fungal growth, flies and pests.
Council records note that grape marc is an industry issue which requires careful management to ensure that there are no adverse environmental effects. Council has been monitoring the land application of winery wastewater annually since 1999 and, in 2016, first prosecuted five vineyard owners over the discharge of grape marc or leachate into water or onto land.
Please refer to local council regulations, which contain specific rules to inform your grape marc storage and use. For example, composting of grape marc requires dedicated compost pads to be built for environmental protection.
Whilst overall an improved management and awareness of grape marc storage was noted by Council in the 2018 vintage year, 37 % of wineries were rated non-compliant during on-site wastewater and grape marc inspections. These inspections found that grape marc is variously stored in a ‘compost-type’ facility on site at the winery, spread immediately under vines or in pastoral lots or it is sent to other rural locations. The disposal of grape marc can be costly, so why not turn it into a useful resource?
Whilst no substitute for applying compost, the beneficial utilisation of this vineyard waste stream, provided it is mixed with Grape Marc Mix, can prove a resourceful, sustainable and environmentally-conscious vineyard management technique. Furthermore, Grape Marc Mix is 100% organic-compliant.