How to Interpret Soil Foodweb Assays

Steps 3 & 4

Step Three:
Fungi must be present to perform their functions of competing with the more difficult disease-causing organisms, retaining nutrients especially micronutrients like Ca, and making macroaggregates which form air passageways and hallways to allow air and water to move into the soil, and to allow good drainage. This is a critical step in improving soil structure, but cannot occur without the first step of good bacterial biomass.

The "correct" density of fungal biomass, or amount of fungal activity, has just begun to be established, based on observation of these levels in different soils, climates, conditions, disturbances and plant species. Seasonal variations and the requirements of different plants appear to be the most important relative factors. Again, the values for active fungal biomass and total fungal biomass are given for the season, plant type, soil type and climate in the row marked "desired range".

1. 1. When total fungal biomass is too low, fungi will need to be added back to the soil, compost, compost tea or to the water, in hydroponic situations, for example. Add them back by using a healthy, aerobic compost or compost tea. Alternatively, these fungi might be found in healthy soil, especially the humus layer of a healthy forest. But be careful not to destroy that resource by removing too much, or disturbing too much.
2. When total fungal biomass is high, most of the time this means improved ability to perform fungal functions, but if the balance between total bacteria and total fungi becomes inappropriate for the plant species, then the balance needs to be restored. However, you don’t kill off fungi if they are higher than the desired ratio, you improve bacterial biomass instead (see Ratios).
3. On rare occasions, total bacteria may compete with fungi for food resources, and in this case, reducing bacterial foods may be a good idea, to allow the fungi to have a chance to grow. High total fungal biomass, combined with too low active fungal biomass may indicate a fungal disease outbreak in progress. This can be confirmed by examining the roots for necrosis, galls, or other signs of fungal disease.
4. Beneficial fungi require aerobic conditions and if oxygen falls below 5.5 to 6 mg oxygen per liter, then the beneficial fungi may not survive. Anaerobic bacteria attack and consume fungi in these low oxygen conditions. Disease-causing fungi are benefited by anaerobic conditions, either because they no longer have competition from the beneficials, or because they require anaerobic conditions for best growth. In either case, anaerobic conditions select for and allow the disease-causing organisms to "win" in the fight for plant tissues.

Step Four:
Just like any other creature, fungi require food. Feed the beneficial fungi, if fungal activity is too low. Sloughed root cells and dead plant tissue often supply the more complex carbon substrates that fungi require, such as cellulose, cutins, lipopolysaccharides, complex protein-sugar-carbohydrate, and lignins. Fungi are good at condensing organic matter into ever more complex forms, such as fulvic to humic acids. Fungi need N, P, K, Ca, and all the other nutrients as well, and obtain those from organic matter and from inorganic sources as well. Many species of fungi can solubilize mineral elements from the mineral components of soil, but no one species effectively solubilizes ALL minerals. A diversity of species is needed to obtain all nutrients.

Often soil tests will indicate that some nutrient is in low supply, but merely by adding the appropriate bacterial or fungal species, these organisms will convert plant unavailable nutrients into plant available forms. Diversity is the key, however, as well as feeding that diverse set of species so they will perform their functions.

Both bacteria and fungi are important in holding nutrients in the soil when they would otherwise leach into deeper soil layers, and into ground water. The importance of microbes in forming soil structure and preventing erosion is well-known, but in order to hold the nutrients in soil, bacteria and fungi must turn them into biomass, which is not-leachable as long as the glues and strands that the fungi and bacteria use to hold themselves on any surface are not destroyed.

1. If activity is low, then fungal foods need to be added to increase growth rates and improve numbers. A diversity of foods needs to be added, and thus dead leaf material is a much better choice than purified cellulose. Fish hydrolysate also adds bacterial foods, and N and other micronutrients. Wood, sawdust, bark, paper and cardboard can be used as well, but diversity is key.
2. If activity is higher than the desired, then try to balance the ratios of the organisms by improving the organism group that is too low.
3. If active fungal biomass is low, but total fungal biomass is high, this is a good indicator that disease is either rampant, or about to be rampant. Add BENEFICIAL fungal foods and build soil structure as rapidly as possible to compete with the disease, and protect the plant roots from the disease.
4. In rare instances, it may be because some environmental disturbance occurred that put the majority of the fungi to sleep, but did not kill them.

< Steps 1 & 2 - Steps 5 >