By Navona Gallegos. This is the second article in a series of two. Read the first part here.
Liquid compost amendments are simply techniques to spread a small amount of compost over a larger area by mixing it into water. There are several ways to do this. They all take into account the fact that soil organisms make glues to help them stick to the organic matter in compost. In order to get the organisms evenly distributed over an area, we have to get them unstuck from the organic matter and suspended in water and then spread this mix over the desired area in such a way that the organisms survive the journey. Before we get into the specific techniques, there are a few considerations that apply no matter what method you choose.
Key Considerations
Keep it aerobic – While there are some approaches to inoculation that use anaerobic organisms or go through an anaerobic phase, for the purpose of this post we’re considering aerobic compost and aerobic organisms. The maximum level of ciliates in the the BioComplete™ standard (see previous blog post) is a way of ensuring that compost has not reached low oxygen levels that then create conditions for anaerobic (no oxygen) or facultative (low oxygen) organisms. This is important because plant and animal pathogens all occur in these low or no oxygen conditions. Obviously, we do not want to be inoculating with disease-causing organisms. Furthermore, when a liquid amendment that’s full of beneficial aerobic organisms goes anaerobic, many of the beneficial organisms die or go into dormancy. It only takes twenty minutes of anaerobic conditions for anaerobic organisms to start eating the precious aerobic fungi that are usually the main focus of our inoculation!
Therefore, it’s absolutely crucial that our liquid amendment stays aerated. One way to do this is to use an aquarium bubbler and keep the liquid at a “rolling boil” level of aeration. This can be helpful if you are leaving a batch overnight or for a few hours before applying. Don’t leave a liquid amendment sitting for more than two days, even if you keep it aerated.
If you are making a liquid amendment on the spot in order to apply it right away, you can simply stir the liquid well and create a vortex that draws in some air. This can be done by hand and should happen about every ten to fifteen minutes.
Preparing compost extract in the field. Images by Isabelle Jenniches CC BY 2.0
Water – Most municipal water contains antibiotic compounds like chlorine and fluoride. In addition to killing water-born diseases, these compounds can also kill the beneficial soil organisms. Luckily, humic acid, which can be bought at most grow stores or ordered online, can be used to neutralize these antibiotic compounds. All that’s needed is a couple drops per gallon of water. Simply use a dropper to add one drop at a time of humic acid until you start to see the water turn a slightly brown color. Once a color can be seen, it means that the humic acid has bonded with all of the chlorine and/or fluoride and it’s safe to add the compost.
Temperature – The best temperature for water intended for a liquid amendment is around room temperature. This is convenient because some techniques involve getting your hands wet. If it’s comfortable for you, it’s probably good for the organism too. Water that’s approaching steaming is too hot. Cold water may not kill organisms, but it shocks them and many will go straight into dormancy. This can slow the results of your inoculation as it will then take a while—perhaps days or weeks—for the organism to wake up again. It’s best for our organisms to be active when they land on the soil or plant so they can be motile (mobile) and find the right niche for themselves.
Don’t smash the organisms – When we make a liquid amendment, we may want to use equipment like a backpack sprayer to apply it. In this case, we have to filter out the organic matter from the liquid so we won’t clog equipment. If we are filtering an amendment, the filter pore size must be 400 microns or larger, or else some of the organisms won’t get through. It’s easy to find 400+ micron bags for sale online.
It’s also important that we don’t spray so hard that the pressure kills the organisms when they collide with plants or soil. A simple way to determine this is to spray a piece of paper from about arms length away. If we damage that paper at all, then the pressure is too high. One way to reduce pressure is to simply get farther away from the target we’re spraying. If you spray in a big ark, even if the organisms come rocketing out of the sprayer, they will have time to slow down before they hit ground and have a softer landing.
Keep out of the sun – Soil organisms mostly live underground and out of the sun’s UV rays. It’s advisable to keep compost and liquid amendments out of direct sunlight. Unless you are making a compost tea, where the organisms grow and make UV resistant glues in the process, it’s best to apply liquid amendments early in the morning, on a cloudy day, or in the evening. My favorite is the latter because I have a hunch that it’s helpful for the organism to have all night long to migrate to their ideal soil depth before the sun comes up. It can also help to water right after inoculating, especially in a dry area, so that the organisms can literally swim down into the soil to get to the depth they prefer.
Keep equipment clean – It’s easiest to clean equipment when it’s wet, just after use. When equipment like sprayers get slimy build up of biofilms on them, those films can house disease causing organisms. It’s also important to make sure any spraying equipment that has been used for fertilization or pesticides has been cleaned very thoroughly with soap to make sure there are no harmful residues.
How much water and compost to use – This is a common question and as with most things ecology the answer is: it depends. Generally, we can say that it takes about five pounds of biocomplete level compost to inoculate one acre. However, if you find a really great compost that has, say, 1,000 micrograms of fungal biomass as opposed to the 135 microgram minimum, you could only use two pounds per acre for a good inoculation.
I prefer to go as heavy as possible when inoculating. When I successfully treated late blight in tomatoes, I used about five pounds of compost for an area that was only about one hundred square feet. As long as the compost is good quality and doesn’t contain harmful organisms, more is generally better.
The amount of water is simply dictated by how much water is necessary to cover the area you are inoculating. Whether you use a lot of water or a little, it is still the same amount of compost being added. Generally, it is best to err on the side of more water because you can always come back and add more liquid amendment to an area you have already covered, but if you run out of liquid and you’ve used all your compost, then there’s an area that did not get treated. For reference, I have used 300 gallons on one acre and about 40 gallons on a 500 square foot backyard. However, it all depends on what kind of equipment you are using and how fast it sprays. When in doubt, try a test patch with just water and see how much water it takes to spray that area, or how much your watering can cover, then scale up to calculate the water it takes for your whole treatment area.
Liquid inoculation techniques
Compost slurry – This is probably the easiest liquid amendment to make. It’s just what it sounds like: a slurry of compost in water. One way is to use a paint stirring paddle on the end of a drill and use the slowest drill setting to spin the compost into the water. Do this for ten minutes. Again, it’s important to keep the drill on the lowest possible setting so the organisms don’t go hurtling into the walls of your bucket or container and smash on impact. It’s even possible to make a slurry by simply using a stick or your hand to mix the compost and water. It’s just important that it is mixed for at least ten minutes and stirred hard enough so that a vortex is created. This slurry can then be sloshed around the area you are inoculating using buckets or any equipment that won’t get clogged by the organic matter.
Compost extract – The only difference between an extract and a slurry is that we filter the extract so that it can be applied using equipment that would get clogged by a slurry. The idea is the same: separate the organisms from the organic matter so that they float in water. Even if you are going to use hundreds of gallons of water, it is fine to extract all of your compost into a five gallon bucket and then add that highly concentrated extract to whatever larger water vessel you will use. You can also make the extract straight into a big tank if that’s easier. The main benefit of doing it in a bucket first is ease of handling, and also, if you would like to look at your extract under a microscope, it will be concentrated enough that you can see many organisms easily in a sample.
My favorite way to make compost extract is by hand using a 400 micron filter bag. Simply fill the bag with about two pounds of compost at a time, put it under water, and squeeze the bag over and over for five minutes (see video). Once you’re finished, dump out the used compost (in an area you want to inoculate–there will still be organisms that didn’t get extracted), and add the next chunk of compost to extract into the bag and repeat. It’s kind of like making tea except it’s more active; you will see the water get darker as the humates from the compost ooze into the water. There’s some technique involved as well; it’s important not to grind the compost against itself as if you are scrubbing it. The correct technique is to simply squeeze over and over as if you are squeezing–but not wringing out–a wet sponge. Move your hand around the bag so you get all parts of it.
You can also use a paint paddle on a drill on a low setting and spin for ten minutes in the same way you would for a slurry. Then simply pour that slurry through a 400 micron bag to filter out the organic matter.
It is also possible to use an aquarium bubbler to make an extract. Fill a 400 micron bag with compost (use multiple bags if you are using more than five pounds of compost), put the bag in water, and leave the water bubbling at a “rolling boil” level for at least four hours. I like to leave the bubbler going for five or six hours. This can be a nice technique if you are using a compost tea brewing device and making a big batch of compost extract. You can set it up in the morning, leave it brewing in the shade during the day, then apply late afternoon or evening.
Compost Tea – Compost extract and compost tea often get confused with one another. The difference is simply that in an extract the organisms are being extracted from the organic matter and floating in water while a tea is brewed for a period of time with foods that help the organisms grow while they are brewing. The benefit of making a tea instead of an extract is that a tea is good for foliar applications while an extract is better to apply straight to the soil surface. If treating a nasty foliar disease, tea might be very helpful. The process for making a tea is the same as an extract with some additional steps: after preparing the extract as explained above, microbe foods are added to the mix and the tea is brewed with an aerator for one or two days (not more than three). When brewed in aerated water with foods such as humic acid, plant oils, fish oils, etc., the organisms receive an abundance of all the things they need for growth. After a day or two of brewing, the organisms will have hatched from cysts, grown in size, and/or produced more of those glues that make them sticky. So when they are applied straight to plant surfaces, they really do stick! We can also promote the growth of certain desired organisms in the brew based on the foods added. If we want more fungi, we add humates and oils, if we want more bacteria (unlikely) we may add sugars.
However, making a compost tea can be tricky because adding foods means that the organisms may grow so fast that they run out of oxygen. Then, we run into all the issues already discussed about anaerobic conditions and organisms. The brew can go from being beneficial to being dangerous for plants. Therefore, I only suggest making a compost tea if you are also able to use a microscope to monitor its progress.
Generally, organisms from a healthy soil will make their way onto plant surfaces eventually, especially if plants germinate in that soil. Furthermore, a healthy soil microbiome means that the plant will have the nutrients it needs to make its aboveground parts resilient to pests. So, a compost extract applied to soil can still be beneficial to above ground issues and is much easier to successfully use than a compost tea.
Along with mulching, inoculating with a compost extract is my favorite way to quickly boost soil and plant health. It’s something that can be done any time of year and can have profound results. If you have any questions about inoculation, please feel free to get in touch. And check out New Mexico Healthy Soil Working Group’s field day schedule for hands-on learning about making inoculant quality compost that can be used for these techniques.
Navona Gallegos is a soil ecologist and lover of life. Her passion for the wholeness of nature led her to study terrestrial ecology and specialize in soil biology. Navona’s educational background includes a BA in Environmental Science from the University of Virginia, Starhawk’s Earth Activist Training Permaculture Design Course, and Dr. Elaine Ingham’s Soil Food Web School as well as lived experience as a farmer and informal learning from a wide variety of land stewards from across the United States, Caribbean, and Central Africa.
David Gude
Wow. These two articles are great. As new to Mew Mexico home gardener and a Master Gardner intern I plan to use this info NYT thanks.