The Effects of Compost Tea Applications to Soil on Microbial Activity.

Bacteria and fungi are the driving forces behind the decomposition and mineralization of organic matter and are critical components in the cycling of nutrients. Throughout this process, these organisms release CO₂ as a product of their activity. As a result, CO₂ can be used to monitor microbial activity. More specifically, changes in CO₂ production via microbial respiration can be used to evaluate land management practices and their associated impact on the soil biology. Recently, the addition of organic and biological amendments, such as compost teas, have gained favor as an alternative method of maintaining plant health, boosting plant productivity, and improving soil health. Compost tea is a highly concentrated solution of beneficial microbes and nutrients that are extracted from compost. However, there is little evidence in the scientific literature to support this recommendation and many of the claims regarding the benefits of biological amendments remain anecdotal. The objective of this experiment  was to monitor changes in CO₂ flux from the soil, which is indicative of microbial activity through respiration Tests were conducted using 1quart mason jar microcosms fitted with a 2-way valve for CO₂ sampling. Each microcosm housed a sterile cup filled with 50 grams of forest soil and  was placed in an incubator at a constant temperature to eliminate environmental variables. Ten replicates of five treatments were evaluated. The treatments included; reverse osmosis water (control), recommended application rate, 1/2 full strength, full strength compost tea added to soil and one treatment that consisted of only compost tea (no soil) added at full strength to a sterile cup. CO₂ concentrations within the sealed microcosm were evaluated prior to treatment, and 24, 48, 72, 120 and 168 hours after treatment. This was done using a syringe to draw air samples from the headspace of the sealed microcosms. At the moment the lids were sealed samples were drawn and then again four hours later. All air samples were stored in 10 mL glass vials. This was completed at every sampling period and analyzed by a SRI gas chromatograph for CO₂ concentration. Concentrations provided from the gas chromatograph allowed us to see differences between applications based on the increase in CO₂ concentrations.