The living soil: encouraging soil fungi

John Seymour was not a great fan of compost. In his book of self-sufficiency he asserted that you can make the best compost in twelve hours by passing it through the guts of an animal. But nevertheless, he provided information on how to make the best compost, but this was his concession to those readers who did not keep animals. Seymour was writing at a time when compost and manure were seen as merely forms of obtaining nitrogen,potassium and phosphorus, but there is another element in compost that was not properly appreciated in Seymour's time. Seymour, writing in the 1960s, was already falling out of date, for the extra ingredients of compost that are not present in manure are fungi and glomalin.  

Sir Albert Howard was a man who thoroughly deserved his knighthood, unlike many who have gained it despite sharp business practices and for political donations.Howard was one of the founders of the organic movement, and in the 1920s at his Indian research station he led the way in development organic agriculture. It was in the course of his investigations that he came upon a discovery. He was having to find a way to restore the tired soil in tea plantations, and as an experiment  he added a thin layer of compost, to find that crops revived. Further investigation revealed that he had not added a great deal of fertility over and above what the soil already had, so he realized that there was something else in the soil that was enhancing fertility. The extra ingredient was soil fungi, for the crops were working symbiotically with the fungi. Howard was only at the  beginning of the long discovery process, but later scientists have learned that the fungi and the plants trade nutrients with each other, the plants providing the fungi with sugars, the fungi providing the plants with trace elements. This was an example of evolution in action, for plant and fungus had evolved in partnership with each  other. [Howard reveals his thoughts in his book, An Agricultural Testament.]  

Shortly afterwards Rayner, working for  the UK Forestry Commission in Dorset, South West England, discovered mycorrhizal fungi. These are not the fungi with which you are familiar from walks in the woods, for they rarely see the light of day. They are vast interlacing underground network that live in close harmony with trees and other plants. Lack of these fungi in the soil means that plants become stunted as they are deprived of the nutrients that the fungi provide. 

In 1996 Sarah Wright, working for the US Agricultural Research Service, hit on a new discovery: the mycorrhizal fungi were coated in a then unknown substance, glomalin. Working in the Henry A Wallace Beltsville [Maryland] Agricultural Research Center she found that glomalin was a superglue for soil. A form of carbon it binds soil and tilth particles together in a powerful bond. We had previously thought that it was only humus that did this job, but now Sarah has shown that glomalin serves as a super-bonding agent. And what is more, it might account for up to a quarter of the soil's carbon.     

So what's is happening? Any fungus is a vast network of threads known as hyphae. Sometimes they spread through the soil and other times through living creatures. Much of the time they are positive for growers, but there are fungi that can be parasitical that damage trees and plants, such as honey fungus, Armillaria, which destroys trees and renders their wood useless. But mycorrhizal fungi are always positive. 

The network of hyphae interlaces the soil and penetrates plants through their roots. Then it spreads through the plant until it finds a plant cell that is sending chemical signals that it is short of a specific nutrient, then the hyphae get to work. They penetrate the  cell through a network of threads that emerge from the hypha and pass on the required nutrient, and in return the fungus receives the sugars derived from photosynthesis in the plant's leaves. As fungi do not photosynthesize they rely on plants for sugars and in return provide minerals.

Now here come the glomalin. This superstrong form of carbon provides rigidity for  the hyphae, so that when they cross a gap that might make them sag,they have the rigidity of girders. Furthermore, the powerful carbon bonding glues soil particles together, and this is vital for the cohesion of soils. Without glomalin and humus the world's soils would disintegrate.

Firstly, you do not have to rely on nature alone for your mycorrhiza, for you can purchase them from various stores. Applying the fungi is easy. When you dig your planting hole, sprinkle the fungus in it. Some growers suggest that the night before you plant you moisten the rootball by immersing it in water in which the fungal spores have been put. This gives them time to coat the rootball, and the results will be good for your plants, but it is sufficient to spread the powder.  Some growers use a spray. It is important that the fungus is in contact with the roots, as  it is still in spore form when applied, but contact with root exudates causes the  fungal spores to germinate, which is what you want. 

But there are implications for horticultural and agricultural practice. Scientists have noted that when soils are dug the levels of fungal presence deteriorate as the networks are broken up. Deep ploughing is detrimental to fungal well being. This has been seized by the no dig school of horticulture, but there are times when you need to dig,plough or harrow. My personal preference is the limited digging model, in which you only dig and plough when necessary. Some form of digging is necessary if you want to create tilth, the fine soil in which vegetables thrive, and you need to dig when you plant potatoes and other root crops. Digging also replicates the work of rooting animals, such as pigs, which are a natural part of the ecosystem, so some digging cannot be harmful, just do not do too much of it.  

There is also  the need for farmers and gardeners to apply compost properly. Patience is the key. Don't hurry your compost, allow it to ripen over a few months, for the heating of the heap destroys soil fungi, but the slow ripening process allows them to return from the soil beneath the compost heap and recolonize it. Farmers, who have been no great users of compost, are now looking seriously at it as they are recognizing its value. There is also biochar,that wonderful soil enhancer,  for it is thought to be excellent for the development of glomalin in the soil. If you apply both compost and biochar then you are likely to develop a good fungal network in your soil. 

But there is another strategy that we should follow:minimize the use of artificial fertilizers, for fungi cannot stand them, which is why when these artificial substances are used, fungal levels drop.Mary Reynolds, writing in The Garden Awakening, speaks of how the white explosions of mushrooms that coated Ireland's  fields in Autumn [Fall] are now gone, as the farmers began to apply artificial fertilizer instead of manure. These mushrooms provided a source of food for some people, and their loss is not a blessing.