We found a mushroom in our black soil country this week, which was very exciting for us. This country has been in perennial pastures for 4 years now, but before this, had a history of years of chemical use and fallow periods. We think this is a pretty good indicator of the soil health improving as Derek has never seen one on this black soil farming country before… ever. My Dad talks of taking box trailers full of mushrooms to the Sydney markets, which he picked as a kid from the pastures in their paddocks at Yass, in southern NSW (Australia). Whilst there are still mushrooms about, they are not of this quantity that they once were and it got me thinking about fungi, which led me to mycorrhizal fungi.
It’s pretty clear that mycorrhizal fungi are a wonderful advantage to have in soils – you will even hear the benefits of it touted in conventional farming circles! Let’s examine it a little more though – because when we understand the potential benefits of something, is when we begin to value it enough to encourage it and work out how we can incorporate it into our farming systems.
Unlike mushrooms, mycorrhizal fungi exist in obligate symbiotic relationships with plant roots. What does this mean? This means that the mycorrhizae are entirely dependent on the plant roots for their survival – they cannot exist without the plant roots. They rely on the liquid carbon containing exudates from the roots of their host plants. You will no doubt be familiar with the appearance of fungi – with the strand like threads of hyphae that they produce. These hyphae grow into the tips of the roots and extend out into the surrounding soil – seeking nutrients like N, P, S, Zn and Boron, as well as moisture. It seeks and supplies these things for the plant in exchange for the carbon rich root exudates which it feeds on for energy. [private]The mycorrhiza readily access these soil nutrients with the help of other soil microbes; specifically, bacteria that live on the tip of the mycorrhizae’s hyphae, producing enzymes that solubilise nutrients that would otherwise be unavailable to the plant.2 This is a smart system, as the nutrients are stored in the soil in an unavailable form until made so by the mycorrhizae and their associated bacteria. This means that the nutrients are not at risk of being leached from the soil. Advantages of plant colonisation by mycorrhizae are reflected by their 10-20% faster growth rates than plants not colonised by the fungus.3
You may have heard mycorrhizal fungi explained as an extension of the root system of the plant. And a very effective one too – the hyphae of the fungi can spread to up several hectares! “The absorptive area of mycorrhizal hyphae is approximately 10 times more efficient than that of root hairs and about 100 times more efficient than that of roots.”4 The sheer size of the mass of the hyphae mean the plants can access greater soil moisture and the hyphae reach small micropores in the soil, that plant roots are unable to access.
Mycorrhizae protecting plants from insect damage
A study released last year shows that not only do mycorrhizae do all the great things mentioned above, but that they are also responsible for communication between plants.
It was already known that plants communicated via volatile organic compounds (VOC’s), which are odorous compounds the plant releases to ‘warn’ other plants of insect attack. “The plants respond by emitting different VOCs that repel aphids and attract aphid-hunting wasps.”5
An experiment was conducted with broadbean plants, where a group of plants were infested with aphids and then sealed inside clear plastic bags that prevented the VOC’s from travelling to the other plants (but allowed the passage of CO2 and water vapour through). Plants from both the infested and non-infested groups were connected via mycorrhizae.
After 4 days, when aphids and parasitic wasps were introduced to the previously uninfected plants, it was only the plants connected via mycorrhizae to the previously infested plants that were repellent to the aphids and attractive to wasps.6
Similar studies have been done since, which indicate similar communication among plants about impending drought and insect attack and there is even initial evidence that plants may be communicating through sound!, but that’s not for now.
So, in having systems that discourage the flourishing of mycorrhizae, we are losing this ability for plants to act in this signalling manner. This may go partly the way to explaining why pasture croppers describe a complete lack of need for insecticides and fungicides on the crops they grow. With crops being sown into perennial pastures, there is surely some mycorrhizae that would be present that may be acting in the way described above.
What hinders mycorrhizae in our farming systems?
There are several things about common farming and grazing practices that are detrimental to mycorrhizae.
Fallows
Many croppers will be aware of the term long fallow disorder – which relates to crops not thriving despite adequate moisture. The reason for this ill thrift is attributed to a lack of mycorrhizae – and this disorder occurs after long fallow periods and droughts – when there have not been growing plants present to host the fungi. The plants then suffer as a result of limited access to nutrients like phosphorus and zinc. This can also occur in crops that follow another crop that is not a mycorrhizal host – such as canola.
Pesticides and Fertilisers
There is some evidence to suggest that a moderate soil working will actually do less harm to mycorrhizae than the use of chemicals will, 7 while other information indicates that the use of herbicides may not be detrimental to mycorrhizae.
Given the symbiotic nature of the fungi and host plant, in the presence of high rates of artificial phosphorus fertiliser there is no need for the mycorrhizal fungi to go seeking phosphorus to supply to the plant, as the P already sits there, readily available. The natural nutrition cycle is therefore disrupted and the mycorrhizae won’t do their job and may not even colonise the root as a result.
How can we encourage mycorrhizae in our farming and grazing systems?
The more we feed the mycorrhizae with soluble carbon from roots – the more they will deliver nutrients back to the plant and eventually carbon to the soil, in a stable form. So, living roots are a key. This means trying to replace fallow periods with live plants where we can. This could mean cover cropping or pasture cropping, replacing annual fodder crops with perennial pastures.
It has been suggested by Dr Christine Jones that “broadacre cropping could benefit enormously from widely spaced rows or clumps of long-lived perennial grasses and/or mycorrhizal fodder shrubs. As yet we do not know the required critical mass to improve soil ecosystem function, but it might only need to be 5-10% perennial cover.”8 Because of the large nature of the underground hyphae systems of the mycorrhizae, this wide spacing may be enough to host the mycorrhizae that the fungi are then perpetually present in the soil. A diversity of species in these rows would be of benefit too.
Interesting idea…. This is essentially what Grant Bain has in done Western Australia – which you may recall from my pasture cropping blog. Grant’s sub-tropical pasture is planted on wider row spaces, which he then pasture crops among.
What other species could you imagine working as a perennial row in cropping country?
A fairly different idea, but don’t you think we need some paradigm shifts in order to discover better ways to farm and graze? And we also need BRAVE farmers willing to give different things a go.
There is the ability to inoculate plants/seeds with mycorrhizae, but there will also likely be some background level of inoculant in the soil. Testing can be taken out to determine levels – either of roots of living plants, or of soil from fallowed ground. Remember however, that regenerative farming is not about applying one product and expecting miraculous change – it’s a whole system approach.
References
1 Mycorrhizae – New Worlds Explored. http://planthealthproducts.com/category/mycorrhizae/ 12th Sept, 2014.
2, 3, 4, 7 & 8- Jones, C – Mychorrizal Fungi – Powerhouse of the Soil. Evergreen Farming, Sept 2009. http://www.amazingcarbon.com/PDF/JONES-MycorrhizalFungiEVERGREEN(Sept09).pdf 12th Sept 2014.
5 & 6. Cossins, D. 2014 Plant Talk. The Scientist. http://www.the-scientist.com/?articles.view/articleNo/38727/title/Plant-Talk/ 12th Sept, 2014.