Aug 082013

Photo © Bulleen Art & Garden

For over 400 million years there has been a mutually beneficial relationship between the root tips of plants and mycelium (fungus).

The term ‘VAM’ – Vesicular Arbuscular Mycorrhiza – is used to describe one such type of this beneficial relationship between the root tips and the fungi.

The mycelium enters the root tip and together they form a site where nutrients and carbon can transfer. This assists the plant in absorbing the essential nutrients for growth. VAM is an additional way the plant has of absorbing nutrients, and makes it possible for plants to grow in conditions that are suboptimal (nutrient deficient) – such as many Australian soils. Without VAM, the direct uptake of nutrients by plants via their root systems can result in a nutrient deficiency in the soil immediately adjacent to the root zone. Subsequent absorption of nutrients is then limited by the rate at which roots can grow into new soil and by the rate at which nutrients move through the soil. With VAM, the extensive network of mycelium grows past the depletion zones and allows nutrients to be actively transported into the root system. This method is a much more efficient way of maintaining contact with nutrients than the plant continually extending its root system into fresh soil.

Benefits of VAM

The benefits of VAM are many and well documented. VAM inoculants have been available commercially in agriculture (and hydroponics) for some time and are only now being packaged in sufficiently small quantities to be available for use in the home garden (1kg and 150g bags instead of large drums).

There are many benefits of adding VAM inoculants to the home garden and they include:

  • Increased establishment and survival of seedlings (fungi enter the emerging roots and rapidly establish the beneficial relationship aiding survival and successful establishment)
  • Higher growth rate and greater plant size
  • More and better quality fruit and leaves with a higher nutritional value.
  • Increased tolerance to drought
  • Increased tolerance to pests and diseases

Due to the symbiotic nature of the relationship between the fungi and the plant root tips, if you leave an area fallow (no plants in it) the fungi will die. Consequently, in your vegie garden, if you don’t want to grow a winter crop after your summer crop, rather than leave the patch fallow we recommend you sow a green manure crop.

There are many other benefits of VAM, here are some links if you would like to investigate further. Click here for a good over-view of mycorrhizza. For an extensive discussion on VAM, its modes of action and application in agriculture / horticulture, click here and follow the links.