Whats up PGS blog readers… Lets talk about foundations for gardening success…. MICROORGANISMS. Here at PGS we are about to embark on a scientific journey. We are going to brew several compost tea formulas available, put them under a microscope, and post our results, but first we need to understand what we should be looking for.

Compost tea is a water extract of compost. By adding select food substrates to the compost tea, the micro-organisms in the compost are encouraged to multiply and grow exponentially.

As the microbial numbers increase, the dissolved oxygen levels decrease. Thus it is imperative that air is continually bubbled through the system to keep the extract aerobic. The brewing period is complete after 48 hours and the compost tea – which contains nutrients (organic compounds, micro and macro elements) and a wide variety of beneficial bacteria, fungi, protozoa and nematodes – can then be applied as a soil drench and/or foliar spray. The effectiveness of the compost tea depends on the quality of the compost, the extraction efficiency of the compost tea system and the ability of the food additives to enhance microbial growth without affecting the microbial diversity.

A nematode that feeds on bacteria (bacteriovore). In the nematode’s “gut” small spots of bacteria can be seen. [400 x magnification]

Most protozoa in compost tea feed on bacteria. Here a cilliate (a genus of protazoa) can be seen. They have very small hair-like structures (F), called cillia, that move the fluid and bacteria into its vacuoles where it is digested and nutrients absorbed. Notice the tail-like structure (A) it uses to anchor itself to a piece of organic matter. The dark piece in the left bottom corner is a small particle of organic matter. [400 x magnification]

This protozoa, a cilliate, has the same feeding mechanisms as the one in the figure above. Here four “heads” can be seen on the one tail-like structure. All four are actively feeding on bacteria. The dark piece is a small particle of organic matter. [400 x magnification]

Here another genus of protozoa, an amoeba (A), can be seen. Small, round protozoa called flagellates (B and C) are also visible. [400 x magnification]

compost teas can have specific fungal food additives which increase the fungal biomass in the tea. Here fungal strands called “hyphae” can be seen surrounding pieces of organic material. [400 x magnification]

Why use compost tea?

Natural systems, like fynbos, are healthy and require no input from man for their fertiliser and pesticide needs. Thirty percent of the sugars produced by plants through photosynthesis are excreted through the roots to feed the micro-organisms in the soil. The exudates differ between plant species and select for different combinations of microbes. Diversity in plants means diversity in microbes. These microbes in turn protect the plant against disease by covering potential infection sites, out competing disease-causing organisms for food and by inhibiting their growth. Certain microbes predate other microbes; this keeps disease-causing organisms in check. It is estimated that 75% of all insect pests spend part of their life cycle in the soil. A healthy soil with diversity in beneficial soil organisms and high organic matter content helps keep pest populations below the economic thresholds.

Bacteria and fungi are rich in protein which contains high quantities of nitrogen. Nutrient retention occurs when these organisms multiply and absorb free nitrogen, which they convert to protein in their bodies. In the spring, nitrogen, mobilised in bacteria and fungi, needs to be converted to plant-available forms. This is achieved when the bacteria and fungi are eaten by protozoa, nematodes and micro-arthropods.

In the conventional agricultural approach, soils become marginal and depleted of organic matter, essential nutrients and micro-organisms. A plant that grows well in nature will need constant attention and expensive inputs in a system where monoculture is practiced. The root exudates of the crop can only feed a limited variety of microbes. This limits the amount and diversity of beneficial organisms and they are further reduced by pesticides and high doses of fertilisers. Natural predators are lost and pests and diseases become rife. More and more chemical inputs are needed, costing the farmer dearly. For instance, four to six times more nitrogen is applied by the farmer than is actually used by the crop. Soil fertility and plant health will be greatly enhanced by the microbial diversity found in Ecosoil’s compost tea, especially when used as an integral part of a holistic management program. This in turn will result in financial gain as less chemical inputs will be needed.

Advantages of compost tea

• Elimination of compaction. Dramatic results have been seen in as little as 2 years.
• Lower fertiliser requirements. Less leaching of fertiliser. The improved root system intercepts and utilises fertiliser better. Many growers cut fertiliser by 10 to 20 percent in the first year of application. In the second season further fertiliser cuts can be made due to the carry-over effect.
• Fewer weeds. The type and amount of weeds change over time as soil biology changes.
• Greater root volume and more feeder roots. Compost tea will make compost in sito by breaking down dead organic matter. Roots utilise the nutrition released by microbes and form a web of feeder roots right to the soil surface.

Feeder roots growing into decomposed wood

• Healthier plants and less need for pesticides. A healthy soil will produce healthy plants. Your crop will be less stressed and will have greater resistance to disease.

Chenin Blanc with 3 compost tea soil drenches and 4 foliar fungicides. These vines show far less symptoms of downy mildew (Keimoes, Northern Cape)

Chenin Blanc with no compost tea soil drenches and 6 foliar fungicides. These vines show a high incidence of downy mildew compared to those shown above, despite being treated with greater quantities of foliar fungicides (100 m away from compost tea treated orchard)

• Increased production. In most cases production increases of between 10 and 20% are seen. (See farmers comments and research section)

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