Fungi and bacteria are the primary recyclers of nutrients in the soil, decomposing complex organic compounds and returning their minerals to the soil the next generation of plants and animals. So what should you be doing to look after them?
Fungi are responsible for greater amounts of nutrient retention and soil organic matter (SOM) formation than bacteria so let’s have a closer look at the three categories of fungi and the roles that they play in the soil.
Firstly there are the decomposers, the Saprophytes. These, along with some bacteria, are the great recyclers in nature breaking down complex materials into simple molecules that can be used by fungi and other organisms. Saprophytes play key roles in soil organic matter formation because of their ability to help decompose dead plant and animal remains, such as animal hair, hooves, claws and feathers including animal dung. A succession of saprophytes colonise debris on the ground. Sugar fungi break down simple sugars. These are eventually replaced by brown rot fungi, which digest cellulose and hemicelluloses and, when they have accomplished their work, leave behind a brown, crumbly residue rich in lignin. The white rot fungi that replace them have the ability to digest lignin, the residue most resistant to decomposition, and leave behind wood strips that look bleached and stringy. The use of fungicides and weedicides can severely hamper the functioning of this group of fungi. A prime example of this occurring is poor stubble break down.
Secondly there are the parasites. These are the second largest group of fungi, of whose members do a lot of serious damage preferring a living host, often attacking and killing it. The presence of a host plant is necessary for parasitic fungi to proliferate. Normally, they are specific to certain crops or species, but some can affect several plant species. Continuous planting of the host plant will encourage growth of parasitic fungi, so it is an advantage to promote high biodiversity in farm soils.
Thirdly there are the mutualists, the Mycorrhizae. These fungi form symbiotic relations with about 85% of all plants, including trees and most field crops, sending their hyphae in and about the smaller roots. The plant supplies moisture and carbohydrates, and the mycorrhizae returns the favour with minerals and other nutrients from the surrounding soil. Most plants grow better whilst many plants could not survive without the mycorrhizae which protect roots from soil- borne disease-causing organisms and parasites. Mycorrhizae also produce glomalin, a type of protein, which is important in soil aggregate formation. It acts as glue, binding plant cells, fungi, bacteria and microorganisms with soil particles to form larger particles of organic matter. This glomalin helps make the soil more porous thus helping water infiltration and drainage.
So how do you ensure that there are plenty of good fungi at work in your soils? These days many farmers add commercial preparations of VAM (Vesicular Arbuscular Mycorrhizas) at sowing time to help good growth and strike rates. However in soil conditions where nutrient levels are very low or very high, particularly when there is an excessive supply of phosphorus, mycorrhizae can become ineffective. This is also the case when farmers apply chemicals such as insecticides and fungicides that can decimate mycorrhizal populations, while herbicides may remove the very plants that affect fungi distribution. For active mycorrhizal fungi to thrive build soils with ample organic matter, rotate your crops with little or no tillage.