Compost Teas: Brewing a Sweet Blend

Understanding the Value of Castings

Castings added to the soil carry to the root zone a rich compliment of soluble plant nutrients and growth enhancing compounds, a diverse and populous consortium of microbial life and a substrate of organic matter harboring a storehouse of nutrients that are not lost to rain and irrigation. The plant is delivered an ongoing, reliable food source when bacteria and microscopic fungi feed on the organic matter, releasing some of the nutrients to the soil and storing others for their own energy and reproduction. When nematodes and protozoa in turn feed upon them, the nutrients stored in the bacterial and fungal bodies are released to the soil in a plant-available form.

According to Dr. Elaine Ingham, Director of Soil FoodWeb, Inc. of Corvallis, Oregon, when soil, compost or castings support protozoa numbers on the order of 20,000 per gram of solid matter, 400 pounds of nitrogen per acre are released through their predation of bacteria. When we feed organic matter to the soil, the soil life feeds nutrients to the plant.

Further, unlike soluble plant fertilizers, the nutrients stored in organic matter and the bodies of the microbial life are not lost through irrigation to contaminate ground water. Hair-thin fungal tentacles, called hyphae, wrap about soil and organic matter particles in their search for food, forming aggregates that are the basis for good soil structure. Thus, both the fungi and the organic matter are held in the soil. Bacteria exude sticky glues that enable them to cling to solid particles of mineral and organic matter, ensuring they too remain in the soil and, like the fungi, aid in the formation of aggregates.

Nutrient retention and cycling are not the only benefit to castings use, however. By inoculating the soil with the rich, diverse, microbial life present in good worm castings, the plant root is protected from disease and attack by root-feeding organisms. Because the diversity of organisms aids in ensuring everyone present has a predator, no one organism in the root zone is easily able to reach populations sufficient to cause significant damage. Plant roots exude foods that encourage colonization by microbial life beneficial to the plant, reducing the number of possible infection points. Many micro-organisms exude compounds inhibitory to pathogenic organisms, further reducing the chance for pathogen blooms sufficient to cause plant damage.

When we add castings and the microbial life they support to the soil, we aid in increasing the complexity and diversity of organisms in the root zone, thus aiding in disease and pest suppression. It may not be in the root zone alone where worm castings demonstrate the ability to suppress pest attack, however. There is a growing body of research suggesting that castings derived from a feedstock of plant materials are rich in a compound called chitinase. Chitin, a component of the exoskeleton of many insects, is damaged by chitinase, leading some researchers to believe its presence in the castings may be inhibitory to some insects. Research being conducted in California is demonstrating suppression of white fly and ambrosia beetle in some tree species when castings containing chitinase are applied at the root zone.

From Castings to Tea

So, "why tea?" one may wonder. With compost and worm products demonstrating such tremendous benefit to soil and plant life, why take the extra steps to generate a liquid from this already understood and easily applied solid material?

Leaf surfaces, like plant roots, harbor a rich microbial population that protects the leaf, and thus the plant, from infection and attack by pathogenic organisms. When the microbial consortium present on the leaf surface is reduced by pesticide use or environmental damage, it exposes leaf surface, opening infection points. We can reinoculate the leaf with the diverse com-munities of microbial life found in compost and worm castings by applying a tea made from these materials. Further, teas can be applied as soil drenches and root washes after pesticide use, to reintroduce to the soil microbial communities that may have been damaged by the pesticide. The microbes can then continue to provide protection from pathogens to the plant as well as aiding in breakdown of any pesticide residues in the soil, thereby preventing ground water contamination.

Teas also carry the soluble nutrients and beneficial growth regulators contained in the solid matter used to make the tea. Many of these compounds can be absorbed through the leaf surface, feeding and enriching the plant.

Tea or leachate?

The microorganisms present in an aerobic compost or vermiprocessing system require significant amounts of moisture in order to break down the organic materials present. They use the water in b
References :