Organic and biodynamic viticulture is good for soil, grapes and ultimately the quality of wine – but in the current environment it comes with a potential financial penalty for growers.
That is the key finding of a recently completed six-year project carried out in McLaren Vale by researchers from the University of Adelaide. It was funded by AGWA, with in-kind support from Gemtree Wines, the McLaren Vale Grape Wine & Tourism Association, Peats Soils and others.
With organic and biodynamic practices forecast to grow at more than 11 per cent per annum, the project set out to determine its relative sustainability compared with both low-input and high-input conventional viticulture.
The trial was carried out within a 10 hectare planting of 20-year-old Cabernet Sauvignon vines. Initially, it was intended to run for just three years to assess the effects of converting from conventional management to organic and biodynamic management as part of a PhD project undertaken by Luke Johnston. It was extended after changes in soil and vine parameters did not become apparent until the third year.
The final report – prepared by chief investigators Chris Penfold and Dr Cassandra Collins and collaborators Prof Petra Marschner and Assoc Prof Sue Bastian – concludes that while winegrape production is one of the easiest forms of primary production to manage organically or biodynamically, the achievable yields are frequently lower and production costs higher.
During the trial, yields for organic, biodynamic and low-input conventional viticulture were 79, 70 and 91 per cent respectively of the yields achieved with the high-input conventional viticulture treatment, due to weed competition for soil moisture in the undervine zone. This outcome was reflected in the gross margins analysis, which showed the organic, biodynamic and low-input conventional viticulture systems generated 74, 65 and 91 per cent of the financial return per hectare of the high-input conventional viticulture system.
Higher operating costs associated with the use of tillage for under-vine weed control also contributed to this result. In this calculation there was, however, no premium applied to the prices received for organic and biodynamic fruit.
Depending on region these may be up to 100 per cent, which helps compensate for the lower yields and increased production costs.
The researchers note that for some growers, other aspects of winegrape production – such as improvements to soil and wine quality – are more important than financial returns. In this project, sensory evaluation by a panel of local viticulturists and winemakers found significant benefits for wine quality once organic and biodynamic practices have had time to have an impact.
Panellists noted little difference between wines made in 2010 (the first year wines were made from the trial) but for the following four years, organic and in particular biodynamic wines were consistently described as being more rich, textural, complex and vibrant than low- or high-input conventional viticulture wines.
‘These findings support anecdotal evidence from winemakers who have used this language as a reason for why they have chosen to make wine from organically and/or biodynamically managed fruit,’ the report says.
‘How wine compositional changes relate to the textural changes perceived by winemakers in the wines made from these systems is yet to be determined.’
Important in the assessment of an agricultural system’s sustainability is its impact on soil properties. In the trial, the maintenance of plant growth undervine and use of tillage rather than herbicides for weed control generated more microbial carbon and larger earthworm populations. While not impacting on vine growth, the application of compost also had desirable impacts on soil quality.
The final report is available on the AGWA website