Compost Tea: An organic additive for plant health

Compost tea is a liquid compost prepared by brewing the 'compost extract' (made by suspending stable and mature compost in water at a ratio of 5:1) with some microbial nutrient source such as sugars, proteins, oat meal, soybean meal, and/or humic acids at a constant temperature. The aim of brewing is to extract beneficial microorganisms from the compost, followed by growing this microbial population during the brew period. The dark-colour solution that leaks out of the bottom of the compost pile is not compost tea. These are the leachates that may contain some pathogenic organisms in addition to the presence of soluble nutrients. Therefore, they are not considered suitable for foliar spray. Compost tea can be aerated and non-aerated. Non-aerated teas are made by simply mixing the compost, water, and other ingredients and allowing them to ferment with little or no disturbance, whereas the mixture is mechanically aerated to create aerobic conditions in the solution for preparing aerobic tea. Anaerobes produce metabolites that can harm the plant tissues very rapidly. Putrefying organic matter contains organisms that are not beneficial for plants. Under aerobic condition, there is little possibility of growth of human pathogens. The more diverse the community of microorganisms extracted and grown under aerobic conditions better will be nutrient retention by the tea. Compost tea has been reported to offer more measurable benefits in stimulating crop growth, yield and quality and disease suppression.

Precautions for compost tea preparation
• Only potable water needs to be used to make compost tea or to dilute it.
• All the equipments used to prepare compost tea should be properly sanitized
• Composts to be used should be mature and stable.
• The foods added to the brew vary with type of tea required: bacterial or fungal tea. If a fungal brew is desired, complex material as oatmeal, soybean meal, flour, humic acids, fulvic acids (which will release bacterial foods after fungi begin the process of decomposition) are added.
• Avoid adding molasses, when fermenting compost tea, as these can promote the growth of harmful organisms
• Temperature of brewing should be related to soil temperature
• Oxygen in the tea should not fall below 5.5 to 6 ppm dissolved oxygen, which is typically about 70% dissolved oxygen.
• The tea needs to be analyzed for toxicity, absence of pathogens (Clostridium, Listeria, Streptococcus and Enterococcus) and adequate population of beneficial organisms (Bacillus, Fluorescent Pseudomonads offer disease resistance to plants) before its application.
• The time length, the tea is brewed is approximately 18-24 hrs.
• Compost tea should be applied to the soil within 5-7 hours of its preparation. As the solution is rich in microbes, nutrients may get depleted on prolonged storage and on finished brewing.

Plant benefits
If done properly, compost tea is a concentrate of activated microorganisms, more concentrated than compost itself. It is easy to use liquid and can be convenient for any horticulture application
ï'˜ Provides nutrients to plants and soil and adds beneficial organisms
ï'˜ Adds soluble nutrients to soil or on to foliage of plants
ï'˜ Application of fungicides, herbicides and chemical fertilizers reduce the population of agriculturally important microorganisms. The application of compost tea to soil fills the gap by building the population of beneficial microorganisms
ï'˜ Improves nutrient availability in root system
ï'˜ Results in nutrient retention in soil
ï'˜ Reduces the use of chemical fertilizers and loss of nutrients into ground water
ï'˜ Helps to suppress plant diseases

Compost tea and its role in disease suppression
A mixed response of compost tea on disease suppression has been reported. It may be due to variation in microbial population as well as the severity of disease. Effective bio control potential of compost tea against fungal damping off in tomato has been observed. Approximately 50% suppression in powdery mildew disease has been reported in grapes due to application of compost tea during first year of its application. Its failure to suppress powdery mildew on Howden pumpkins in first year, but reduction in the number and size of pathogen colonies in the succeeding year has also been observed. A slight reduction of gray mold, along with an increase in the level of downy mildew, has been recorded in the compost tea treated plot during the first year at vineyards. Compost tea did not reduce severity of late blight on Superior potatoes when disease was present in second year.
The efficacy, consistency, and practicality of using compost tea for disease suppression needs to be evaluated considerably before being recommended for application.

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