We are posting part 2 of our interview with Elaine Ingham Ph.D, President and Director of Research at Soil Foodweb Inc.

Dr Elaine Ingham, Ph.D outlines the carbon cycle

According to Elaine,  compost tea should be applied in order to replace missing beneficial organisms on the surfaces of plants so those surfaces will be protected. Those organisms should be present in high quality aerobic compost and given optimal brewing conditions, extracted  into the compost tea. This layer of protection prevents the growth of pathogens that might compromise your plant, either on the roots or above ground.  Generally our purpose is to nurture high numbers of the beneficial organisms that are in the compost, but which will grow in the ambient conditions of the brewing process. Brewing tea specific to the plant’s requirements is wise, since what you apply will be specific to the plant’s root exudates (exudates feed the biology which is associated with the plant).

So Elaine, can we discuss some different ways that we can select for the biology that’s missing from soil?

We commonly recommend employing different methods when producing compost tea so that the biology that’s missing in the soil can be added. First it’s very helpful to be able to test the soil so that you’re not guessing. It’s easy to take a shotgun approach by making a ‘balanced’ compost tea, but whan we do this, we’re just guessing. We run the risk of compromising the desired organisims in our compost tea when using shotgun methodology. That kind of approach can be just fine when dealing with healty plants.

Can you give us some examples of how we can go about growing the organisms that are missing?

If  protozoa (which are critical for nitrogen cycling) aren’t present  in the soil during a period of vegetative growth, plant development is limited.   To correct this, we must first find compost which has high protozoa numbers. Protozoa eat bacteria which are very high in nitrogen. To get high numbers of active protozoa in our compost tea, we must extend the brew cycle to at least 30 to 36 hours.

In the case of adding fungi and bacteria, it’s more a matter of adding specific food resources to the compost tea. If we are missing bacteria in the soil, we’re able to create a compost tea which is skewed in that direction. This is accomplished by adding some simple sugars, like non-sulfured, blackstrap molasses. In the case of increasing fungal biomass, high carbon and protein based foods such as humic acid and grain flours are added as a food resource.

Tell us about adding nematodes. We know that can be a tricky task.

When there are low numbers of beneficial  nematodes in soil, it’s best to first investigate why they’re not present. Commonly, soil compaction, low organic matter and excessive soil disturbance result in a lack of beneficial nematodes. Only the smaller plant feeding nematodes can survive under these conditions. These factors should be corrected before adding nematode inoculum. In order to efficiently add nematodes to the soil, you must first find compost which has high numbers of beneficial nematodes (which means, aerobic compost,  since beneficial nematodes are strict aerobes) and good diversity.

Bacteria Feeding Nematode

A viable method of improving nematode numbers and diversity is through the use of compost extracts. When making compost tea, most of the organisms in the compost are extracted into the compost tea within a few hours. This is known as a compost extract.  Conversely, when making compost tea specifically for the tea itself,  additional time is needed for the bacteria, protozoa and fungi to multiply. When preparing an extract, microbial foods are not normally added. If your goal is to extract nematodes a short extraction cycle of about 4 to 8 hours will allow many more nematodes to survive. A full compost tea brewing cycle can kill many nematodes. This may be a result of adding too many bacterial foods which drive dissolved oxygen levels too low for nematodes to survive the brew cycle. Excessive agitation in the brewer may also kill the nematodes. It should be mentioned that nematodes do not reproduce during the compost tea brewing cycle. If you don’t want to take 24 to 36 hours to make a tea, consider an extract instead. Extractions will extract the organisms of the compost, but no time is needed to let organisms grow up into high numbers or biomass. Typically, extractions require more compost (say 5 to 10 times as much as a tea), but only take 2 to 4 hours to make, certainly not more than 8 hours.

Just make sure the compost you are using has the beneficial organisms that are missing and that they are extracted, and end up in the extract or tea, and on the surfaces of your plants. If the organisms are lost anywhere along the way (lack of oxygen, filtered out in a filter, or killed by a pump), then you won’t see the benefits of improving biology.

Thank you again Elaine, we’ll check back in with you in a few weeks.

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