Organic viticulture – is it a load of compost?

Thursday, 30 March, 2006
Frank Smith
Swedish soil scientist Dr Holger Kirchmann claims organic farming is no better for the environment than conventional farming methods. Frank Smith reports from Australia.

'When critical scientific analysis is applied, organic farming falls short with respect to nutrient use efficiency, soil fertility, nitrate leaching and nutrient recycling,' Kirchmann told a World Crop Production Conference at Brisbane, Australia, recently. His research shows that organic crop yields are 25 to 45 percent lower than for conventional agriculture. 'The nutrient use efficiency of organic manures is lower than from inorganic fertilizers, because of the lack of synchrony between nutrient release from organic manures and nutrient demand of the crop. Thus, organic farming leads to more nitrogen leaching, despite a lower nitrogen input,' he said. Dr Megan Ryan at the University of Western Australia, who collaborated in Dr Kirkman's research, said all scientific evidence points to the lower yields of organic crops being due to lack of soil nutrients. 'There is no evidence that soluble fertilizers cause increased plant stress. Plants self-regulate,' she told

Organic grape growers, like others, aim for premium quality. 'There is little or no scientific evidence that there is any quality difference between organic and inorganic products,' said Dr Ryan. 'There is no health impact from conventional products and no evidence in the scientific literature of negative residues passing through food or wine to consumers.' Dr Ryan said claims that organic farming improves soil biological activity are pretty much hokum. 'We don't know what a healthy soil is. How do you define it? Biological activity is influenced by soil temperature, water, soil structure and organic matter content. You can increase biological activity if you add a lot of compost. But it is hard to build up soil organic matter. The main way to improve soil organic matter and structure is to adopt a no-till system.

Organic farming can't go "no-till" because of the need to control weeds without herbicide,' said Dr Ryan. But organic growers do not agree. One grower with a solid scientific background is Peter Little of Random Valley Wines, near Margaret River, Western Australia. 'From the start we wanted our vineyard to be organic, but based on science not mythology,' said Peter. 'There is a lot of snake oil in the organic industry.' He began by collecting baseline data on soil and water and gradually applying organic principles so that they achieved certification. Water leaves his vineyard cleaner than when it arrived, with as little as 1mg/L of nitrogen and 0.1 ppm of phosphorus, and he uses no synthetic pesticides or fertilizer. 'No one likes using them. We time our compost applications to meet the needs of the vine's life cycle,' he said. 'Nutrient timing is critical. We carry out a soil analysis in May and draw up a nutrient budget for nitrogen, potassium and trace elements.' His compost is pelleted with trace elements and applied as a mulch between the rows of vines. The mulch keeps the vine roots about 8°C cooler than the top of the mulch. Little aims for carbon based compost with lots of nitrogen, sometimes including fish waste, although he is concerned about its sodium content. Weeds are not a problem. 'Why would you want to control them? Weeds provide biomass and add about 7kg N/ha to the soil every year. Weeds also play a role in maintaining biodiversity. We need to know their function in the ecosystem,' he said.

Little slashes the between-row ryegrass and triticale cover crop in September and again as late as possible in Spring, so no ground is left bare. The ryegrass provides food for garden weevils, allowing the grape vines to develop a vigorous foliage before the weevils attack them. Nearby biodynamic vineyard, Cullen's, uses a tractor-mounted propane steam generator, to cook under-vine weeds. The thirty-year old vines show no sign of damage. Botrytis is Little's only major disease problem. He manages this by leaf plucking to maintain an open canopy. 'If you know you can grow grapes without using chemicals, in a way that is non-polluting and encourages biodiversity, it is irresponsible to do it any other way,' he said. 'I can't see any advantage in conventional viticulture.' He goes on to say that his yields are similar to those of neighbours. 'It took us seven years to get our yields up. Going organic is a slow process. It has taken us ten years. You have to be prepared to wait. Commercially driven vineyards could not afford the time. There is no quality problem, we are a premium fruit producer.'

In spite of her doubts about the science, Megan Ryan believes organic growers are important to the industry. 'Organic farmers play an important role in increasing awareness of the environmental impact of agriculture,' she said. Dr Kirchman, however, is unimpressed. 'Organic farming has become an aim in itself, an ideology that may exclude other more effective solutions to the environmental problems afflicting current agricultural systems,' he told fellow agricultural scientists. Dr Ryan claimed the advantages of becoming certified organic, rather than just limiting chemical inputs, probably lies in the premium price organic growers hope to get from consumers for their label.

Little, not surprisingly, disagrees. 'Organic certification is the only guarantee the consumer has,' he said.