A. 4. Compost Tea

12 steps to repairing the soil food web by Elaine Ingham, PhD

Step One

Bacteria must be present to perform their functions of competing with disease-causing organisms, retaining nutrients and making microaggregates to improve soil structure. The “correct” density of bacteria, or amount of bacterial activity has just begun to be established, based on observation of what these levels are 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 bacteria and total bacteria are given for the season, plant type, soil type and climate in the row marked “desired range”.

1. When total bacterial biomass is too low, bacteria have to be added back to the soil, compost, compost tea or to the water, if working in hydroponics, for example. Add them back by using a healthy, aerobic compost, compost tea or commercial inoculum
2. When total bacterial biomass is high, most of the time this means improved ability to perform bacterial 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 bacteria if they are higher than the desired ratio, you improve fungal 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. Too high bacterial biomass, combined with too low active bacteria biomass may indicate anaerobic conditions occurred, because the bacteria grew very fast, used up the oxygen in the medium so the aerobic organisms went to sleep, but the anaerobes grew well. This can be very detrimental to the aerobic organisms, and actually kill them.

Step Two

Feed the bacteria, if bacterial activity is too low. Just like any other creature, bacteria require food. Plant roots often supply the simple carbon substrates that bacteria require, such as simple sugars, proteins, and carbohydrates. Bacteria need N, P, K, Ca, and all the other nutrients as well, and obtain those from organic matter and from inorganic sources as well. Various species of bacteria can solubilize mineral elements from the mineral components of soil, but no one species can effectively solubilize ALL minerals. Diversity of species to obtain all the needed nutrients is required.
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.

1. If activity is low, then bacterial foods need to be added to increase growth rates and improve numbers. A diversity of foods needs to be added, and thus molasses is a much better choice than white sugar. Fish hydrolysate also adds fungal foods, and N and other micronutrients. Fruit juices 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 bacterial biomass is low, but total bacterial biomass is high, this is a good indicator that anaerobic conditions have occurred. In rare instances, it may be because some environmental disturbance occurred that put the majority of the bacteria to sleep, but did not kill them.

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.

1. 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”.
   
   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. 5. Beneficial fungi require aerobic conditions and if oxygen falls below
4. 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.

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