Nutrition and Drought Effects Workshop


McLaren Vale has had two very dry Winter/Spring Periods in the last three years.

In 2006/07 and 2008/09 vineyard yields (and to some extent Olive yields were reduced). Some vineyards were less than 50% of typical yields. Yields were reduced by a combination of reduced berry set (% flowers turned into bunches) and reduced berry size (berry weight).

Additionally the summers of both 2008 and 2009 had extended periods of heat which had a serious effect on vine and tree health.

With this is mind, Lucia Grimmer, researcher and agronomist with Agrichem visited McLaren Vale to give her thoughts on nutrition during droughts and heatwaves.

Forty grape growers joined us at the Willunga Football Club.

Problems during droughts.

Lucia notes the problems with drought are caused by dry soil. Limited soil moisture causes;

- Limited uptake of nutrients.

- Plant stress. Symptoms like early leaf drop, increased sunburn, increased splitting, thin cell walls and phenolic wine.

- Reduced soil mircobes activity.

- Higher disease in some cases (nematodes; insect damage; fungal disease).


Ask dry soil is the problem she suggested working on the soil is the best place to start.

It is suggested growers start to drought proof their soil by;

- increasing organic matter.

- increasing water holding capacity.

- increasing root growth.

Products that can help.

Humates - Seaweeds - Silica

Humic acid is the most effective way to boost organic matter. Humic acid is the remnants of old coal and leaf litter which has been stable in the soil for eons.

Humates are very stable in the soil compared to other inputs - especially when compared to raw manures. Manures have the added negative affect on plants as they draw down nitrogen. Soil microbes take nitrogen away from plants to break down the manure. Raw manures and green waste can actually plant growth by robbing from the vines. There have been some notable cases where poorly composted, cheap chicken manure has been used in McLaren Vale this year. Ironically this might reduce vine growth - the very thing it is being applied for.
Humates have their positive effect on soil because of their shape. Humates are long chain molecules full of oxygen. These oxygen atoms lock onto water, nutrients and carbon. Plants can then easily take these nutrients up.

Humates can be applied in winter in a granular in a similar way to spreading super. Application rates are 100 to 300kg/ha. The highest rate is recommended on sand.

Cost of applying at the lower rates are $230/ha - comparable with chemical fertiliser rates.

Humic acid is also available in a liquid form. A small amount can be applied as a fertigation product.

Lucia recommends small frequent doses of 1Lt/ha per week. The cost of this application would be $5 per hectare. Therefore repeated ten times it would cost $50 per hectare.



Kelp based products stimulate root growth. More root growth equals more nutrient uptake. Seaweeds contain auxin - a plant hormone for root growth.

As with Humic Acid small frequent applications are ideal. Kelp products can also be applied as foilar fertilisers with your normal applications.


Silica is recommended to be applied to lessen drought effects because it helps strengthen plant cell walls. This helps lessen stress and also has the effect of making insects

Matthew Wilson is looking to trial Silica as a preventative for Phythophtora root rot. It is also likely to help with nematodes control. Silica fertilisers when applied to the roots as fertigation are supposed to be taken into the root and ‘sharpen’ it. It forms glass like plates inside cell walls. Chewing insects have greater difficulty in attacking the roots. Apparently they wear out their mouth pieces. Chetin (crab shells can have the same effect).

For more information visit


Armon said…
Howdy from California Wine Country. I work at a similar company to yours in Sonoma County.

Great website. Great information. I have been selling and recommending humics for about 10 years as a retail Vit Advisor.

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