Comparing Compost Tea and Compost Extract Impact on Microbiology

Compost Extract

For parent materials in the compost.  We used a variety of plant resources from right on the farm.  High-carbon/brown material component consists mainly of aged wood chips.  They are ramial chips from pasture land made from cleared brush and ran through a chipper mounted on the 3-point hitch of a tractor.  A lot of it is buckthorn, prickly ash, and small tree limbs.    The piles are aged so they have started to break down and have an active fungal component already present.  If  leaves are available they will be mixed in for diversity.  

Green material might consist of grass-hay bales, fresh-cut meadow, or a mix of grass-hay bedding and chicken manure.  

High nitrogen materials usually consist of a bale of really nice, green, leafy alfalfa hay and chicken manure.  There is also some horse manure, which with alfalfa as the primary way to heat up the pile.

Following Dr. Elaine Ingham's Soil Food Web method for management of the compost.  Ratios are approximately 50-60% brown/high carbon material, 30% green/grassy, and 10-20% high nitrogen.  Total quantity of materials for each batch is approximately 40 to 50 five-gallon buckets-worth.  Parent materials are well incorporated and hydrated to about 50% moisture, then piled into a chicken-wire container.  We have a compost thermometer and  closely monitor temperature.  We made about six or seven complete batches last year, and by the end the piles consistently reached 150-160 degrees within 24 hours, never letting the piles exceed 175 degrees.  Piles are turned twice, by hand with manure forks and shovels.  Time between turns depends on where the internal temperature tops out, but can range from 24 hours to 72 hours typically.  The goal is to get everything into the hot center of the pile one time, so when we turn the pile it's a very intentional process, not just stirring everything up.  Middle goes to the bottom, top goes to the middle, and bottom goes to the top.  After the second turn, temperature continues to be monitored, with the goal of over 130 degrees and holds there for a couple of days.  After that, the pile is left to cool down and mellow out for about 30 days.  

For the corn, we brewed up a batch of extract using about 10lbs of compost to 200 gallons of water, and applied that in-furrow with the corn at a rate of 5 gallons per acre.  In retrospect, we believe that was too light of an application - both with the amount of compost used in the brew, and with the liquid application rate.  Overall, the corn with the extract actually got taller than the part of the field that received no extract, especially on a clay hill with low organic matter.  Mike dug up half a dozen of each plant and sprayed off their roots, to assess the morphology.  There was no observable difference in root mass between the plants that received the extract versus those that didn't.  

Our main corn crop is a 94-day Brevant Roundup Ready hybrid and a couple of acres of a 94 day non-GMO workhorse variety from Albert Lea seed.  We did a compost application and control area for each type, so we can compare both the treated and untreated areas of the GMO and non-GMO varieties.  Everything received the same fertilizer program.  In total, we had a 16 acre field that we treated half with extract and half without and we also treated another entire 8.5 acre field just because we could.

For soybeans, we brewed a stronger batch of extract - 20lbs of compost to 250 gallons of water - and we applied that with the chisel plow that I modified with thin anhydrous knives to minimize the soil disturbance.  We treated half the field with about 7 gallons per acre, and the other half was left untreated.

Mike dug up three soybean plants from each area - treated and untreated - and looked at the root morphology.  He felt that the plants from the treated area of the field had better root branching and more nodulation.  

Application Equipment

For the application of compost extract,  Mike modified two pieces of equipment that he already owned - a John Deere 7000 four-row planter, and a Kewanee 11 shank chisel plow.  The goal was to keep things as cost effective and simple as possible.

With both pieces of equipment, the intention was to inject the compost extract into the ground.  Mike could have used a crop sprayer to spray the extract on the field surface (and may still try that in the future) but felt that getting the biology into the soil would be a lot better than leaving it on the surface, exposed to the elements.  In the case of the corn planter, applying the compost extract directly into the seed trench, placing the biology right in the same space as the corn seeds. 

For the chisel plow, Mike removed the tillage points from the shanks and replaced them with thin, 1/2 inch wide anhydrous knives.  His intention was to use the chisel plow to inject compost extract into the soil before planting soybeans with a no-till drill.  He would have attempted to install an in-furrow application system on the drill, but it's a rental unit from the local Soil And Water Conservation office, so modifying it wasn't an option. Mike's corn planter is not set up for soybeans, and is still running 38 inch wide rows, so using one piece of equipment for both crops was also out of the question.  Knifing-in the extract ahead of the no-till drill seemed like the next best idea.  Each anhydrous knife has a hose attachment at the heel, which places the extract behind the knife, two to three inches deep in the ground - about the same level as intended planting depth.  Going deeper is an option, but the knives flare out where they mount to the spring shanks, so running any deeper would cause significantly more soil disturbance.

It was easier retrofit both pieces of equipment so that they could use the same pump and reservoir.  That would require the pump to be electric, and the reservoir tank to not  be too big and awkward.  Mike found a plastic 55 gallon drum with a ring-lock lid and gasket that would work as a tank (with some modification), and a used liquid fertilizer diaphragm pump, manifold, and rate controller for sale in an online classified.  Mike had to purchase a number of new hoses, fittings, nozzle bodies, orifice plates, hose clamps and miscellaneous small parts to put it all together.  He also had to construct a framework on both the corn planter and the chisel plow to mount the tank and pump assembly, and find a place on two of our tractors to mount the rate controller and pressure gauge.  Once those tasks were complete, it was fairly straightforward to run the hoses to the row units on the planter, and to the anhydrous shanks on the chisel plow.  All of the hoses and nozzle bodies were zip tied to the equipment framework.  The manifold that came with the diaphragm pump could support up to 16 ports, so it had plenty of capacity.  He simply blocked off 12 of the ports when the system was set up on the corn planter, and five of the ports when moving the system to the chisel plow.

All of this is essentially identical to a basic liquid fertilizer delivery system, which is great because he didn't have to reinvent the wheel.  He just had to acquire all of the pieces and figure out how to make it work for his specific needs.

Making it all Happen

When it comes to actually applying the compost extract for the first time, we did stumble a bit.  Our first issue was that we had no idea what our concentration of our extract should be, or how many gallons per acre to apply.  Dr. Ingham had stated at one point during the Soil Food Web Foundation Course that two gallons per acre should be more than enough if the compost quality is really high.  We figured being amateurs that our compost quality wasn't as good as it could be, so we would bump that up to five gallons per acre.

To determine concentration, we decided to take a sample of our extract and examine it under a microscope.  We needed to choose some sort of marker that we could use to track our extract concentration.  We decided that fungal spores would be our best indicator.  They're relatively easy to identify, and because our primary goal was to increase our fungal population in our soils, fungal spores seemed like a natural fit.  Around this time I had also been studying what Dr. David Johnson (co-developer of the Johnson-Su Bioreactor) used to determine his application rates, and fungal spores were one of his primary methods of measuring concentration as well.

In the spring of 2022, when we applied our first round of compost extract, we mixed the batch to a lower concentration than a previously described, using 10 pounds of compost to 225 gallons of water.  We also didn't know at that point that we needed to agitate the mesh bags of compost in the water to really help rinse out as much of the biology as possible, so the solution ended up being rather weak.  We then applied that batch of extract at 5 gallons per acre to our designated corn and soybean acres.

When I examined a sample of that extract under a microscope and calculated our concentration, I determined that we had applied approximately 6 million fungal spores per acre.  We weren't sure if that was good or bad, so we filed it away for future reference.

Here is the mathematical formula used to calculate  spores per acre:

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I examined several prepared slides under the microscope, each with one drop of compost extract per slide, and counted the number of fungal spores on each slide.  The average was 12 spores per drop.

for the pipettes I'm using, it takes 28 drops to make 1 milliliter
there are 3785.41 milliliters per gallon
we applied 5 gallons per acre

Thus:  12 x 28 x 3785.41 x 5 = 6,359,489 spores per acre

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Later that summer, I had the opportunity to meet Dr. Johnson at a field day, and I asked him what he would recommend for an application rate using fungal spores as a tracking measurement.  He replied that anything less than 56 million fungal spores per acre would be an under-application.  We knew right away that we needed to adjust our concentration and rates.

When we began this whole process, we had envisioned only doing these applications once per year, in the spring.  By late summer of 2022, knowing that we had under-applied our extract during planting season, we had decided to add a fall application as well.

Technical Problems

Throughout the course of this study, a few minor issues arose that we had to contend with.  The main problem with brewing compost extract and running it through any kind of applicator is filtration.  Steeping the compost in 400 micron mesh bags leads to some larger particles getting into the mixture, and these would tend to plug up the orifices on equipment.  We addressed this several ways.

First, we opted to run the lowest manifold pressure possible, while using the largest orifice plates in our applicator nozzle bodies to achieve our desired gallons per acre.  This worked fairly well on the corn planter, since the row units are spaced 38 inches apart.  Metering out 10 gallons per acre allowed for fairly large orifice plates in that scenario, and most particles flowed through without too much trouble.

The chisel plow was another story.  The eleven shanks on that piece of equipment are only spaced about 12 inches from one another, so that means many more nozzle bodies and orifice plates in roughly the same overall width as the corn planter.  As a result, the orifices themselves are considerably smaller and tend to plug up more easily.

Our applicator pump and reservoir assembly had a small inline 50 mesh filter (which is roughly 300 microns, making it smaller than our mesh steeping bags), and that helped to filter out some of the troublesome particulate.  That small filter also tended to plug up frequently when we loaded the compost extract directly from the IBC brewing tote into the reservoir tank on the planter or chisel plow.  It simply wasn't big enough to handle the volume of particulate we had present in the mix.  Some of the particulate would sneak by the filter as well, and that led to frequent stops and lots of time spent cleaning the filter and the orifices out in the field.  Our first round of compost extract application was pretty inefficient and tedious as a result, and we knew we had to do something about the excessive particulate.

We solved this by fitting a large 50 mesh filter onto the outlet port of our IBC brewing tote.  We added cam-lock fittings to the filter on the inlet and outlet sides, so that we could quickly attach the filter directly to the outlet port on the brewing tote, and then quickly attach a 1-1/2 inch flexble pvc hose to the outlet port on the other side of the filter.  We also added a cam-lock fitting to the top of our applicator reservoir tank, so that we could attach the fill hose directly to the reservoir, regardless of which piece of equipment we had the tank mounted on.  With the additional large filter in place, we could pre-filter our extract as it was transferred to the planter or chisel plow, which removed a lot of the larger particles from the compost extract before we headed out to the field.  We still retained the smaller 50 mesh filter on the applicator as well, so between the two separate filters we were able to catch most of the larger particles before they made it to the orifice plates downstream.  Any filtration smaller than 50 mesh or 300 microns will start to capture the biology that needs to pass through the system, so we avoided using any finer screens in our equipment.

I should also note that we use gravity to load both the planter and the chisel plow from the brewing tote.  Because we're working with dormant and live biology, it's prudent to minimize the number of pumps in the system.  Every time microorganisms pass through a pump assembly, some of them are killed.  We knew that if we wanted to be gentle on the biology, we should try to limit our equipment setup to a single pump - the diaphragm pump on the applicator itself.

To that end, we have a high hill in our farm yard where we set the IBC tote when we're ready to load the applicator.  We simply park the planter or chisel plow at the bottom of the hill and hook up the fill hose, and when we open the valve on the brewing tote, gravity does the rest.  I should also note that we initially used a garden hose to fill our applicator.  That was incredibly slow.  It took over 20 minutes to transfer 50 gallons of extract.  With the pre-filter, 1-1/2 inch flexible PVC hose, and cam lock fittings we reduced our fill time to about five minutes.

Compost Tea

We made compost Tea and compost extract and applied it to corn, hemp and soybeans. 

We used 10 pounds of compost put into a burlap sack and tied.  Then we put the sack of compost into a 270 gallon tote, filling it with 250 gallons of water and using an aerator to add oxygen. We added molasses for food to multiply the bacteria, and let the tea make for 24 hrs.

For the compost extract we also used 10 pounds of compost, putting into a 270 gallon tote, filling with 250 gallons of water and using a pump to recycle the water from bottom to top for one hour.  

Making the Compost

We used the Johnson-Su method to make compost from all on farm materials consisting of 25% manure, 25% corn stalks, 25% alfalfa, 25% wood chips and leaves.  

Application of Compost Tea 

Both the compost tea and the compost extract was foliar applied, using a sprayer with a 120 foot boom. We did not have any issues with clogging.  We applied the tea and extract at a rate of 12 gallons/acre.