Soil Trials

Johnny McMillan, Dr Stewart Field, Jason Randall on the trial site

Capturing carbon with biochar

A NEW trial in Marlborough’s “innovation vineyard” is exploring the impact of biochar on soil and vine health. Marlborough Grapegrowers Cooperative (MGGC) viticulturist Johnny McMillan says the project, being run in collaboration with Nelson Marlborough Institute of Technology Te Pūkenga (NMIT), will explore the potential for sequestering carbon while increasing soil moisture holding capacity, nutrient stores and soil microbial activity.

Biochar is created through pyrolysis, heating organic material such as pine slash (but potentially also grape marc) to high temperatures without oxygen. The remaining matter absorbs carbon, and the International Panel for Climate Change has called biochar an important carbon removal technology.

Rothay Vineyard operations manager Jason Randall used biochar in the soil before planting a new block in spring last year, and set aside 10 rows for NMIT researcher and viticulture lecturer Dr Stewart Field to trial with students. Johnny says the innovation vineyard offers opportunities for students to further their research, while Stewart brings a “scientific head” to the cooperative’s projects. “It’s good extension from science to practical application in the field that we can then share with our members to improve what they are doing.” He says the cooperative wants to increase its members’ prosperity in many senses. “Not just dollars in the pocket, but increasing prosperity of their land and future generations.”

In the mainstream planting the biochar was mixed with mushroom compost and bark, then applied to the undervine area before planting, at a ratio of half a tonne of biochar per hectare. But when it came to the replicated trial, undertaken after planting, they applied the biochar in a variety of quantities, from half a tonne to 10 tonnes per hectare.

As well as a range of rates, they used two different types of biochar, and will consider the site as a long-term project, with NMIT degree students looking at vine growth and nutrition as the plants develop. Stewart and Dr Damian Martin, of Plant & Food Research, hope to source funding to assess soil biology under the varying biochar doses as well.

The MGGC is also running a water stress trial, with probes at five different sites in Marlborough – each with different soil types. There has been no irrigation on the sites, where measurements of canopy density and real-time soil moisture have revealed a higher tolerance for stress than typically triggers growers. “We have shown that real value can be added to your winegrowing by measuring both soil and vine water potential. By fine tuning you can not only use your water resource more sustainably, but potentially reduce other input costs while improving fruit and wine quality at no expense to yield,” Johnny says. They will continue the project, including through a dry year, “to see what thresholds we can hold to still maintain yield”.