Monday, June 15, 2009

Mycorrhizal Fungi

Secret weapon in soil.


Mycorrhizal Fungi form a symbiotic relationship with over 90% of all plant species including grapevines. They form a huge extension of the plants root system allowing it to access far more soil volume. In return for sugar from the plant roots mycorrhizal fungi provide the plant with predominantly Phosphorus and Zinc but have also been associated with increased levels of all nutrients, improved water uptake and decreased salt uptake. Mycorrhizal fungi achieve this by increasing the volume of soil the plant can access by 100-1000 times. Add to this the mycorrhizal fungi’s ability to produce chemicals and enzymes to release tied up nutrients and you have a relationship that you really want to encourage.

The American Journal of Enology and Viticulture has published a number of papers (both glasshouse and field trials) showing improved plant function when vines are associated with mycorrhizal fungi.

The picture above shows how VAM are able to access soil nutrients on a much greater scale than plant roots can alone. DJ's has developed our own range of fungi stimulating soil amendments.

In Australian soils mycorrhizal fungi have depleted over time through use of fertilisers, pesticides and tillage. They have now reached levels where they no longer provide benefit to the grapevine or other plants. You can increase your mycorrhizal numbers by inoculating your vineyard using mycorrhizal spores. It is important to look after your fungi once you have started to promote them.

Using natural sources of Phosphorus such as Rock Phosphates or Guano provides slow release fertiliser that encourages mycorrhizal colonization’s. Highly soluble, inorganic sources of phosphorus trick plants, so that they no longer need to feed the mycorrhizal fungi to access soil phosphorus. Over time this decreases the population of mycorrhizal fungi forcing the plant to be more reliant on inorganic phosphorus and other applied nutrients.

In vineyards the other reason for the reduction in mycorrhizal fungi is due to the use of some systemic fungicides. Follow the links at the website www.mycorrhizae.com for more up to date information about which systemic fungicides suppress mycorrhizal colonization. They can help make decision about which fungicides will help you look after the fungi you are trying to promote.

Excessive cultivation also discourages mycorrhizal fungi because every time you cultivate you break the fungal hyphae. This is like continually pruning your vines,there is only so much you can remove before they die. Fortunately most vineyards have very little cultivation and provide an environment that encourages mycorrhizal colonization.

In recent years the research into mycorrhizal fungi has been on their ability to increase soil organic carbon levels. Dr. Sara Wright from the USDA has estimated that 33% of soil organic carbon is from mycorrhizal fungi. This is predominantly due to Glomalin which is the “skin” of the mycorrhizal filaments. As the fungal hyphae live and die they continue to increase soil organic carbon. Increases insoil organic carbon reduces your need to irrigate, as soil water holding capacity increases also.

A photo of a corn plant root colonized with mycorrhizal fungi. The tiny filaments are the mycorrhizal (VAM) hyphae and the round bodies are the VAM spores.

The best time to inoculate your vines with mycorrhizal fungi is at planting. Using a watering can you can drench the vines with mycorrhizal fungal spores. It is the contact with the roots that allows colonization to happen and this easily achieved at planting. Other options including dressing the seed of a covercrop with mycorrhizal spores or applying a solid blend to the soil undervine which contains mycorrhizal spores in it.

Increasing your mycorrhizal colonization will decrease your inputs into the vineyard and improve your vine and soil health. Vineyards actively encouraging mycorrhizal fungi are financially and environmentally more sustainable.

References


If you would like to lean more about mycorrhizal fungi please visit www.mycorrhizae.com or for the more scientifically minded www.mycorrhizas.org.

This is the link to the USDA for more information about Glomalin www.ars.usda.gov.

2 comments:

brian said...

Be careful when buying mycorrhizae. Many of the commercial products have almost nothing in them. For the results of spore counts from common mycorrhizal products check out

http://www.reforest.com/desk/questions/6676/Common+Mycorrhizal+products+tested

to see the results.

James Hook said...

Thanks Brian for the feedback.

I have always been a bit wary of 'buying' things for the soil. Better to develop what is there.