What Is Compost Tea?
The simplest definition of compost tea is:
A brewed, water extract of compost.
Properly made compost must be used, so that the compost tea needs no further pathogen reduction.
Compost tea production is therefore, a “cold brewing” process, allowing growth of the organisms extracted from the compost.
Only if the process remains aerobic will the complex set of organisms extracted from the compost remain in the tea. The complex set of organisms is needed to establish all of the benefits of a healthy soil food web in soil, potting mix, or on the surfaces of plants. Plant growth is typically improved, although the correct mixes of beneficial organisms need to be matched to the type of plant (see Ingham et al. 1985, other papers by Ingham, and the Soil Biology Primer, 1999).
Compost is the main ingredient in compost tea, but in order to increase organism biomass and activity, other foods are added at the beginning and middle of the brewing period. Special ingredients are added to achieve excellent microbial biomass, better plant production, better soil structure, better nutrient cycling and less disease.
Different kinds of aerated and non-aerated compost tea will provide the proper biology for different situations and will be ever-more integral parts of sustainable agriculture.
Sustainable farming is possible, if year after year, the soil is improved and productivity increases. While any one plant species is limited by its genetics, matching the plant to the biology in the soil solves production problems. Natural processes improve soil productivity, and in the natural world, plant species change with time. Plant communities shift from bare soil, to weeds, to grasses, shrubs, trees and then old growth forest. The mythology of modern agriculture is that soil productivity is set, and once a field is put into agriculture, productivity has no choice but to go downhill.
Fertilizer sales people have been heard to say that agriculture depletes soil health and results in loss of tilth. Nutrients are mined out of the soil, ultimately leaving a field devoid of life, plants and nutrients, unless fertilizers are added back into the soil, in plant-available forms. Instead of solving the problem, however, addition of high levels of strictly inorganic, soluble, plant-available nutrients has resulted in an enormous problem with water quality. The nutrients added are no longer held in the soil. As a result, excess amounts of inorganic nutrients have to be added. This is so different from a healthy soil, where the soil holds nutrients, thereby “cleaning up” the nutrients from the water moving through the soil.
Clean water comes out of healthy soil. Why is water coming from “conventional” agricultural fields laden with excess inorganic N, P, S and other minerals? Or if leaching is not occurring, why are the nutrients lost through gaseous emissions? This is not what happens in natural systems.
Change will occur when sustainable agriculture, not extractive, destructive agriculture, is practiced. Pesticides and inorganic fertilizers are not needed, if soil health is maintained. Tillage needs to be reduced to the minimum possible. Disease and pests are not significant in healthy, sustainable systems. Weeds are really just an indication that the system is not healthy. Nature gives growers clues with respect to what is wrong, if the information is read properly. We just need to learn how to read the information being given to us. We reserve the use of pesticides and other toxic materials to the rare situation when some unusual event occurs that harms the biology that should be present.
Only if soil lacks the biology required to convert nutrients from plant-not-available forms to plant available forms would addition of inorganic nutrients result in improved plant growth. If the proper biology is not present, then the soil is sick. Extractive agriculture uses tillage and addition of excessive inorganic nutrients which harm the proper biology. When there was plenty of land for “slash and burn” approaches to farming, and farming was done on small scale areas, the land and the biology could recover between extractive agricultural disturbance events.
But in today’s world, land is not allowed to recover between farming events, and therefore the organisms and the foods to feed them have to be added back into the system without the luxury of “downtime” to recover. The lack of proper biology must be dealt with immediately, for without that set of organisms, soil structure, nutrient retention and nutrient cycling cannot happen or are severely restricted, and disease suppression and protection are practically non-existent. Returning the organisms needed to build soil health is required.
Direct observation methods, especially of active biomass, show that soil biology activity is significantly harmed by pesticides, inorganic fertilizers, tillage and herbicides. The precise impact depends on conditions in the soil. For example, when soil is very dry, and most organisms are inactive, the impacts are limited. But if toxic chemicals are applied when the organisms are actively growing, impacts can be detected.
How rapidly can organisms colonize from another place? Something has to carry bacteria, fungi, protozoa or nematodes from one place to another, and if transportation agents, such as birds, snakes, and spiders, are also dead, how can microbes reach a distant place? Not that many organisms in soil survive a dry, windblown transfer. Where, in the chemically impacted agricultural valleys of modern technology, is there even a source of healthy soil for colonization to spread from? The necessary diversity of organisms was killed long ago. The wind can’t carry what isn’t there.
Therefore, we need to put back the full diversity of bacteria, fungi, protozoa, nematodes and if possible, microarthropods that were killed by toxic chemicals, tillage and lack of foods (organic matter) in the soil need to be put back. Until that happens, people will be forced to use toxic chemicals to attempt to grow plants. Proper nutrition for the plants will be lacking until the organisms that retain nutrients in their biomass are returned to the soil. How do we put back what has been harmed?
It’s called compost. Or compost tea, if the source of compost is distant, and transportation costs are too high. Since compost tea extracts the full diversity, and then grows selected beneficials to high numbers, a small amount of good compost can be extended dramatically.
High quality compost tea will contain the full set of organisms needed, at high biomass and activity levels that your soil needs to become healthy (from the point of view of the plant you want to grow) once again.
Reference: The Compost Tea Brewing Manual Fifth Edition By Elaine R. Ingham, PhD