Organic Symposia

Knowing your nitrogen

SOPHIE PREECE

AFTER 12 years of life lessons about organic vineyard conversion, Nigel Sowman has come up with three keys to success.

Nitrogen management, a considered substitution programme, and substantial trial areas are not what springs to mind for many, with weed control a typical preoccupation, the Dog Point Vineyards viticulturist told nearly 200 attendees at the Organic Winegrowers New Zealand (OWNZ) Organic Winter Symposia in Marlborough late last month.

But weeds can be seen, while an imbalance of nitrogen and carbon is more insidious, only revealing itself when the damage is already done, he said. That’s one of many lessons he’s learned since 2009, with the transition of 270 hectares of vineyard to BioGro Organic certification. “We have had a lot of success with our conversion process over the years, and we’ve also had our fair share of failure,” said Nigel.

One of those failures – a dramatic reduction in yields on a block in the third year of conversion – was bewildering, given the success of another block converted in the same way over the same seasons. But while the conversions were identical, the two vineyards had a different backstory, with one an existing Dog Point block, where Nigel had been pulling back on synthetics and using alternative inputs for some time. The other was a new purchase, and he relates its decline to a nitrogen imbalance in the soil. “Nitrogen management is the hardest part of organic conversion,” he told the audience.

Nigel and other practitioners said it is common for vineyards to thrive in the first few years of conversion, then take a dive in the third. Nigel now believes that is because adding nitrogen in a conventional setting starts “shutting down” the natural nitrogen cycle in the soil, because it is no longer necessary. When that “tap is turned off” under an organic regime, not only is the ability to naturally cycle nitrogen disrupted, but so is the carbon, which will have adjusted in relation to the applied nitrogen, Nigel said. “If you cannot get that nitrogen cycle working again… it’s two years and then downhill.”

He suggested that those looking to convert their vineyard start pulling back on nitrogen inputs well before they start, and instead “supercharge” the soil with microbial inoculants and foods, to put the block on the front foot in an organic regime.

He also recommended a substitution programme, tapping into the plethora of organic products available to enhance soil and plant health, and tackle pests and disease in the vineyard. However, Nigel and others speaking at the symposia emphasised that organic fruit was more resilient than its conventional counterparts, while cover crops consistently “pay dividends” in the management of pest insects.

His final piece of advice was that anyone talking of trial sites for organic ensure they are looking large. If there’s only one spray machine for a block, for example, that whole block should be converted, rather than organics receiving a small slice of the action. Dog Point Vineyards chose to go 100% from the start, so there was a full commitment to conversion, helping build a culture around the change, said Nigel. “Buy-in is easy when there are no other options.”

The Organic Symposia, which was also held in Central Otago and Hawke’s Bay, included presentations on cover cropping, soil health and the growing science around vineyard biodiversity, as well as sessions on sales statistics for organic wines, market insights and natural winemaking. It drew a diverse crowd, including plenty of conventional viticulture practitioners. “I originally thought I would be preaching to the converted,” said Nigel after the event, delighted to see so many people there who have yet to “dip their toes in organics”.