Comparing Compost Tea and Compost Extract Impact on Microbiology

Final report for ONC22-100

Project Type: Partnership
Funds awarded in 2022: $26,159.00
Projected End Date: 03/31/2024
Grant Recipient: Minnesota Soil Health Coalition
Region: North Central
State: Minnesota
Project Coordinator:
Mark Gutierrez
Minnesota Soil Health Coalition
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Project Information


This project will measure and compare the soil health changes from the use of compost extract and compost tea in a soil health system.  One of the advantages to a soil health system is that as the soil biology improves and organic matter is rebuilt this can lead to a reduction of synthetic pesticides and fertilizers needed which can increase a farmer’s profit per acre.  There are a lot of products on the market that will help stimulate and feed the microbiology in soil.  Many of these products promise improvements to the crop.  If a farmer reduces synthetics as a result of their soil health system, but then trades one dependency for another by purchasing commercial biology stimulators, profit per acre is impacted which can reduce the incentive for a soil health system. 

This research will demonstrate that a compost extract or a compost tea is effective in stimulating the biology in the soil and it is a product farmers can create and manage on their farm at a low cost.  This project will target Minnesota crop farmers and demonstrate a low cost solution to improving soil biology.

Project Objectives:
  • Measure and compare soil health changes from 24 hour compost tea in different crop systems (regeneratively farmed hemp, corn, alfalfa, and conventional corn)
  • Measure and compare soil health changes from compost extract
  • Educate about the construction, costs and benefits of homemade compost tea and compost extract
  • Empower farmers to produce their own soil biology stimulants
  • Educate farmers with practical tools to positively transform the environment and local food production using soil science and regenerative agriculture
  • Share results with other farmers through our member newsletter, website, YouTube and a field day


Click linked name(s) to expand/collapse or show everyone's info


Materials and methods:

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:


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


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.


Research results and discussion:

Compost Extract

Physical Observations of Compost Extract 

These farms have been in a severe drought for both years of this study.  We're dealing with living biology, and that biology requires moisture to thrive.  Moisture has been in VERY short supply, so that will have a definite impact on our results at this time.  One of the farmers plans to keep doing these applications for several more years, in the hope for more normal weather conditions, and will be better able to gauge the overall effectiveness of the compost extract.

One of our first observations came in the spring of 2023.  We were out gathering soil samples, and noticed that in our application zones, we were finding a large number of sow bugs and millipedes living in the residue of the previous year's crop.  These are beneficial decomposers, so it was encouraging to see them.  The compost  had been heavily populated with sow bugs and millipedes during the later stage of its decomposition.  We determined that there was some possibility we had introduced them to the application zone, though it's also possible that this was just a coincidence.

Another observation involves increased vegetative growth on our cash crops in the application zone.  One of our test fields has a clay ridge running through it, and this part of the field has very light colored soil and low organic matter.  In 2022, this field was planted in corn, and by mid-summer there was a clear difference in the height of the corn plants where the application zone ended and the control zone began.  The plants that had received the compost extract in-furrow were approximately six inches taller than the plants that were in the adjacent untreated zone.  This was only the case along the ridge.  When I observed the lower part of the field where soil was much darker and the organic matter levels were higher, the difference in plant height disappeared.

Curious, I dug up six corn plants from the application zone, and six from the control zone.  I took these plants back and washed off their roots with a garden hose to see if the treated plants had a more extensive root system.  I couldn't find any physiological difference in the plant roots, however.  They all appeared to be roughly the same.

This same field was planted to soybeans in 2023, and once again we observed more vigorous plant growth in the application zone along the clay ridge.  The soybeans from the treated area were three to four inches taller, had a denser population due to better emergence, had a darker green color to the leaves, and when I dug up several plants from each zone and examined their roots, the soybeans from the treated area had larger root systems and more nodules than the plants from the control zone.  Again, this was only the case along the ridge.  As the soil quality became darker and richer in the lower part of the field, the distinction disappeared.

Our second field in the study, which was planted to soybeans in 2022 and winter rye in 2023, showed no observable difference in crop growth between the application zone and the control zone, with either the soybeans or the rye.  We did observe an increased number of sow bugs and millipedes, however.

In the fall of 2022, after corn and soybean harvest, we applied another round of extract to our application zones on the two fields.  It was at this time that we increased our application rate to 10 gallons per acre, and started using 20 pounds of compost per 225 gallons of water.

With these rate adjustments, and using the same calculation as before, we were now seeing 300 to 400 fungal spores per drop of extract under the microscope, giving us an effective application rate of approximately 300 million to 400 million fungal spores per acre.

We followed this same process during planting season in the spring of 2023, using the corn planter to apply the compost extract in-furrow, and the chisel plow with anhydrous knives to apply the extract ahead of soybeans.  In the fall of 2023 we used the chisel plow to apply extract over all of our test acres following corn and soybean harvest.


Unfortunately, yield results for our farm are going to be hard to quantify.  We harvest a portion of our corn with a corn picker, and the rest with a John Deere 4400 combine.  Neither have any kind of yield monitoring ability, nor do we use any kind of precision agriculture technology on our farm.  Soybeans are similarly harvested with the aforementioned combine.  As such, all I have to go on is my gut feeling about yield differences.

To that end, I feel that yield was improved slightly in both corn and soybeans in the areas of our fields where the elevation was higher and the soil composition was lower in organic matter, lighter in color, and higher in clay content.  In the lower areas with richer soil, I couldn't see any difference in plant growth or yield.

Measuring the test weight of the grain from the treated versus control areas would have been useful as well, but again, we don't have a method for measuring test weight on our farm. 

Soil Test Results

During the course of our study, we gathered soil samples each spring and fall from the application and control zones of each field and sent them to Regen Ag Labs for testing.  In the spring of 2022, these samples from were taken from both fields before any compost extract applications were made, in order to establish a baseline set of results.  In all cases, we had Regen Ag Labs do a Haney test and a PLFA test for each zone.

PLFA Results

We were initially most interested in the PLFA test, since it indicates microbial biomass and proportions of the different types of microbes.  As a reminder, Mike's goal was to see an increase in fungi in soils where the compost extract was applied.

Unfortunately, we did not see a significant increase in the number or type of fungal organisms in our soil during the two year period of the study.  The fungal biomass ranged from about 1.5% to about 7% of the total measured biomass.  Fungal/bacterial ratio ranged from (0.03 : 1) on the low side to (0.13 : 1) on the high side.  So we're still not anywhere close to achieving the desired (1 : 1) fungal/bacterial ratio.

It was interesting to observe that fungal populations were always higher in the fall soil samples than the spring samples.  Also, spring samples tended to show zero arbuscular mycorrhizal fungi (AMF), with all of the active fungi being saprophytic.  This makes good sense given that AMF need living roots to partner with.  Fall samples showed AMF to comprise about half the fungal biomass, with the other half being saprophytic.  Overall fungal biomass was lower than we would have liked to see.

In all of the PLFA test results, protozoa were completely absent.  This was also a disappointment, since we knew we had at least some protozoa present in the compost extract.  Protozoa are essential predators in a healthy soil ecosystem, and help immensely with nutrient cycling by consuming bacteria and producing plant available nutrients.  To see a zero value was disheartening, but I suspect that the drought conditions experienced over the last two years played a significant part in keeping the protozoa populations low.  Protozoa are quick to enter dormancy when conditions become unfavorable, and they are less resilient than bacteria and fungi.  

One last note on the PLFA tests.  The results between our treated areas and control areas didn't vary substantially.  In some cases, the control areas showed higher values than the treated areas.  Total biomass did generally tend to be higher in the treated areas than the control areas, but the difference was often very minimal.

Haney Test Results

As with our PLFA results, Haney test results didn't show a marked difference between the application zones versus the control zones in either of the test fields.  We saw some broad improvements in available nutrients across the board, but this may be more of an indication that our no-till and cover crop system is working, rather than an indication that compost extract applications are causing notable changes to the soil environment.

A couple of notable improvements:

Water Extractable Organic Carbon improved with each successive set of soil tests, increasing from approximately 120ppm to over 200ppm across the board.  Water soluble carbon/nitrogen ratios increased from approximately (10 : 1) to over (12 : 1), and the soil health score improved from a score of approximately 8 at the beginning of 2022 to about 13 by the end of 2023.

Available nitrogen at the beginning of 2022 was about 35 lbs per acre.  This also increased steadily with each testing cycle, and by the fall of 2023 we were averaging about 60 lbs per acre of available N.

One of the largest improvements was in calcium.  At the beginning of the study we averaged about 500ppm of calcium, and that number increased consistently across each testing cycle until the end of 2023 when it had reached approximately 1,000ppm.

Across the board, available nutrients either increased or held at a steady level.  

Final Thoughts

While we didn't see any dramatic quantifiable results in our compost extract study, I feel like the drought conditions over the last two years didn't give us a fair shot at fully understanding the effects of these practices.  To that end, we intend to keep applying compost extract and taking soil samples during our spring planting and fall harvest seasons for several more years, in order to give mother nature a chance to provide us with some more favorable conditions.

That said, there are a few things about our process that I think we could do better.  First and foremost, the quality of  compost could be improved.  While we have achieved a good fungal component in the compost, protozoa, nematode, and micro-arthropod numbers are nowhere near where they should be for a well balanced biological inoculant.  Consequently, Mike has been considering a variety of ways to fix those shortfalls.  Right now he builds compost piles on a concrete slab.  He is going to try building some future piles on bare ground, to help moderate moisture at the bottom of the pile, and allow microorganisms from the surrounding environment a better chance to infiltrate the piles.  He is also planning to start covering  compost piles with a tarp, because we're losing too much moisture with the piles out in the open and exposed to the sun and the wind - particularly during the hot, dry summers.

We felt that it takes too long to make good compost.  We needed easy water access with the ability to manage flow.  We found that you cannot just dump water on, but need to add it slowly and mix it in.  We felt it was very time consuming to manage the compost and that it takes a lot of compost to apply to a lot of acres. We also felt we needed a microscope to assess quality of compost. We shipped the compost off for analysis and found that we were successful at increasing fungi in the compost but ended up very heavy on bacteria.

Did not see any yield differences or visual differences during growing season. 

Better off using a diverse mix of cover crop and graze ruminants over the soil to achieve balanced fungal to bacteria ratios.  If those options are not available compost tea and extract could be a good tool to increase fungi overtime.  Need to do a really good job on the compost to have success.   

Participation Summary
3 Farmers participating in research

Educational & Outreach Activities

2 Consultations
1 On-farm demonstrations
1 Workshop field days

Participation Summary:

42 Farmers participated
5 Ag professionals participated
Education/outreach description:

We hosted a field day August 22 at Mike Seifert's farm in Jordan, MN.  We had 42 people in attendance.  We demonstrated how to make a compost pile, presented best practices for compost and demonstrated how Mike modified his equipment to utilize the compost extract.  We also toured the fields where we did the trials and discussed Mike's soil health system.  While in the field we demonstrated a few soil health assessments; infiltration rings, shovel test and compaction.

Learning Outcomes

15 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key changes:
  • Making compost - Our field day demonstration on how to make compost to build biology showed a simple hands on tutorial for how to make healthy compost.

  • Application - Our hands on demonstration of how to modify equipment to apply compost educated farmers that for a small amount of money, they can modify equipment they already have to apply compost tea to their crop.

  • Soil biology - farmers heard how the biology of their soil impacts compaction, moisture, yield, insects, weed pressure. Using compost can help increase tor balance the fungal/bacteria ratio in their soil.

Project Outcomes

3 New working collaborations
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.