Abstract
Organic and biodynamic viticulture is forecast to grow at over 11% per annum yet there is little information on the benefits or otherwise that can be attributed to these systems of grape production. With industry funding, a six year trial at McLaren Vale in South Australia investigated the changes in soil health, fruit production and wine quality. Organic and biodynamic production led to improved soil quality, with more soil organisms including much greater earthworm populations. Wine quality was also improved, but in the absence of price premiums, this was achieved at a financial penalty to the grower through reduced yields and increased production costs.
Summary
Organic and biodynamic viticulture production is expanding as growers seek to improve fruit quality, reduce their environmental footprint and improve grower financial returns. To increase our understanding of the function of the alternative (organic – ORG and biodynamic – BD) systems when compared to the commonly practiced low-input (LCON) and high-input conventional (HCON) approaches, a six-year field trial was conducted in the McLaren Vale region of South Australia. The trial site was incorporated within a 10 ha planting of 20 year old Cabernet Sauvignon vines.
Soil chemistry showed little change between treatments over the trial period. The vines were growing in soil that was inherently fertile, and they have low extraction rates for nutrients. Soil biological properties (microbial biomass carbon, respiration, earthworm numbers and biomass) as measured in the under-vine zone, were higher on the ORG and BD, most likely due to the soil organisms’ nutritional requirements being supplied by the plant growth that was maintained rather than removed with herbicides. The application of compost had desirable impacts on soil quality, increasing total organic carbon (TOC), microbial biomass carbon (MBC), pH, electrical conductivity (EC) and phosphorus (P) levels. Vines on the HCON treatment showed higher petiole concentrations of boron (B), with P and sulphur (S) higher on LCON and HCON.
The results of trials and surveys conducted elsewhere found that organically produced grapes yielded less than conventional production systems, as water soluble fertilisers and herbicides for weed control were not able to be applied. Those outcomes were supported in this trial, where the ORG, BD and LCON systems yielded 79%, 70% and 91% respectively of the HCON treatment, probably due to reduced soil moisture availability at budburst. Cultivation using a dodge plough was the main method of weed control on the ORG and BD treatments, but yield had been suppressed by the time this was implemented.
Traditional measures of fruit quality such as total soluble solids, pH, titratable acidity, anthocyanin and phenolic levels in the juice and berries were not found to be consistently different between management systems and with or without the addition of compost. Differences in wine compositional analysis were observed in some seasons. Wines made from HCON management were generally higher in alcohol as well as anthocyanin and phenolic levels compared to the other management systems.
Wine sensory evaluation was performed by a panel of viticulturists and winemakers from the McLaren Vale region. Panel members were asked to undertake a blind tasting of all wines and write down any attributes they perceived in the wines. This language was then analysed using word frequency analysis to determine if certain descriptors were used more often for particular wines and if this corresponded to the management treatments. No differences in the language used to describe the wines made in 2010 were found. In the 2010-2014 wines, ORG and in particular BD wines, were consistently described as being more rich, textural, complex and vibrant than LCON and HCON wines. These findings support anecdotal evidence from winemakers who have used this language as a reason why they have chosen to make wine from organically and/or biodynamically managed fruit. How wine compositional changes relate to the textural changes perceived by winemakers in the wines made from these systems is yet to be determined.
A critical aspect for growers considering the adoption of alternative management practices is knowing whether it will be financially beneficial. In this trial, a gross margins analysis showed the ORG, BD and LCON systems generated 74%, 65% and 91% of the financial return per hectare as the HCON system. This was principally due to reduced yields and higher operating costs associated with the use of tillage for under-vine weed control. It is suggested that the grazing of sheep or mulching the under-vine with straw may reduce water use by the vineyard floor cover, and thereby improve grape yields. It is also possible that the payment of premiums for higher quality ORG or BD fruit would help redress the higher costs of production.
Winegrape production is one of the easiest forms of primary production to manage organically or biodynamically, but as often occurs, the achievable yields are lower than a conventional system. This project has reinforced this notion, but has also shown there are considerable benefits to the broader ecosystem associated with ORG and BD production, such as improvements in soil quality. Growers wishing to adopt systems involving lower chemical inputs therefore have the choice of either improving on their conventional management practices to improve soil quality or use the ORG or BD system but recognise that yields and income may be reduced.