Let’s face it, “fungus” is a dirty word to fruit growers who immediately picture mold and fungal diseases attacking their plants and fruit. However, there are countless different types of fungi, and the great majority are not harmful. Some have even formed partnerships with plants for mutual benefit. Mycorrhizal fungi attach to plant roots and then colonize the surrounding soil with microscopic rootthreads called hyphae. A plant that is colonized by mycorrhizal fungi can uptake as much as 100 times more nutrients.
Over many millions of years, some plants have come to rely on mycorrhizal fungi to the point where they no longer develop their own network of fine soil-foraging roots. Some examples of mycorrhizaedependent plants are berries, grapes, asparagus, melons, peaches and plums. These plants do not have root systems that can effectively search out nutrients, and they find it hard to survive without their fungus partner.
It is true that plants with inefficient root systems can be grown without mycorrhizal fungi, but they will require abnormal amounts of fertilizer. This is where the term “heavy feeder” comes from. If a plant needs more than very small amounts of low-analysis fertilizer to produce good crops, it’s not really a “heavy feeder” but a fungi-dependent feeder, and even with heavy doses of fertilizer such plants may not perform well.
It is humanly impossible to duplicate the full range of macro, minor, and trace nutrients brought to a plant by mycorrhizae. Synthetic NPK “plant foods” can be lethal to beneficial soil organisms, which then creates an even greater plant dependence on human feedings for survival. This is a good thing for the fertilizer marketing companies, but not so good for the grower, as the soil gradually becomes lifeless, compacted, and salty.
For modern growers, soil biology should receive at least as much attention as soil chemistry. (Actually, if the soil biology is right, then the chemistry will be right, too.) The idea that growers need only perform chemical “soil tests” and then “add what is lacking” is beginning to be replaced with the recognition that living organisms in the soil are extremely important to plant performance and fertilizers can be harmful to soil.
Putting mycorrhizal fungi to work may seem almost too simple. A one-time inoculation of spores on roots at planting time and then avoiding high-analysis fertilizers is the general strategy. Blending compost into the soil before planting and then maintaining a permanent mulch cover will provide nearly all the nutrients fruit-bearing plants need.
To gauge the existing level of mycorrhizal colonization (if any), a laboratory examination of the plant roots can be conducted. A general rule of thumb is: The worse the soil, the more plants are likely to benefit from mycorrhizal inoculation. The presence or absence of large numbers of earthworms is usually a good indicator of the soil’s current biological health. (For soil or root bioassays, contact BBC Laboratories (480) 967-5931 or www.bbc-labs.com)
Don Chapman, President
BioOrganics, Inc. - www.bio-organics.com - January, 2001