Soil Food Web Gardening...with compost teas

Soil Food Web Gardening
...with compost teas​

...(text from the book, "Teaming with Microbes" written by Jeff Lowenfels and Wayne Lewis) ​

...any questions or comments about the book are welcome, I'd love to discuss it.
...+ REP if you like.



....the rules!
1) Some plants prefer soils dominated by fungi; others prefer soils dominated by bacteria.
2) Most vegetables, annuals, and grasses prefer their nitrogen in nitrate form and do best in bacterially dominated soils.
3) Most trees, shrubs, and perennials prefer their nitrogen in ammonium form and do best in fungal dominated soils.
4) Compost can be used to inoculate beneficial microbes and life into soils around your yard and introduce, maintain, or alter the soil food web in a particular area.
5) Adding compost/ compost teas and its soil food web to the surface of soil will inoculate the soil with the same soil food web.
6) Aged, brown organic materials support fungi; fresh, green organic materials support bacteria.
7) Mulch laid on the surface tends to support fungi; mulch worked into the soil tends to support bacteria.
8) If you wet and grind mulch thoroughly, it speeds up bacterial colonization.
9) Coarse, dryer mulches support fungal activity.
10) Sugars help bacteria multiply and grow; kelp, humic and fulvic acids, and phosphate rock dusts help fungi grow.
11) By choosing the compost you begin with and what nutrients you add to it, you make teas that are heavily fungal, bacterially dominated, or balanced.
12) Compost teas are very sensitive to chlorine and preservatives in the brewing water and ingredients.
13) Applications of synthetic fertilizers kill off most or all of the soil food web microbes.
14) Stay away from additives that have high NPK numbers.
15) Follow any chemical spraying or soil drenching with an application of compost tea.
16) Most conifers and hardwood trees (birch, oak, beech, and hickory) form mycorrhizae with ectomycorrhizal fungi.
17) Most vegetables, annuals, grasses, shrubs, softwood trees, and perennials form mycorrhizae with endomycorrhizal fungi.
18) Rototilling and excessive soil disturbance destroy or severely damage the soil food web.
19) Always mix endomycorrhizal fungi with the seeds of annuals and vegetables at planting time or apply them to roots at transplanting time.



Compost Tea---- Compost tea puts the microbiology back into soils. It's a good thing because there's some practical problems associated with the other 2 options, compost and mulches. Besides the effort of turning a compost pile, if you have a decent-sized garden and lots of trees and shrubs, carting compost and mulches around and applying them can be hard work. You also have to have lots and lots of both if you are working on anything but a small yard. But what are the chief problems with compost and mulches? They take a while to reach the rhizosphere. And neither mulch nor compost sticks to leaves. Plants generate exudates from their leaves, attracting bacteria and fungi to the phyllosphere, the area immediately around the leaf surfaces. As in the rhizosphere, these microbes compete with pathogens for space and food and in some cases can protect the leaf surfaces from attack. You cannot immediately introduce this microbiology into the rhizosphere, or into the phyllosphere at all, with compost or mulch.
Actively aerated compost teas, on the other hand, are usually easy to apply---both soil and leaf surfaces---and are put right where they are needed. They are a fast, inexpensive, and definitely fascinating way to manage soil food web microbiology in your yard and gardens, handily overcoming the limitations of compost and mulch.


What AACT is not

Do not confuse actively aerated compost tea with compost leachates, compost extracts, or manure teas, all of which have been employed by farmers and gardeners for centuries.
Compost leachate is the liquid that oozes out of compost when it is pressed or when water runs through it and leaches out. Sure, these concoctions get a bit of color and may have some nutrient value, but leachates do little to impart microbial life to your soils: the bacteria and fungi in compost are attached to organic matter and soil particles with biological glues; they don't simply wash off.
Compost extract is what you get when you soak compost in water for a couple weeks or more. The end result is an anaerobic soup with perhaps a bit of aerobic activity on the surface. The loss of aerobic microbial diversity alone (not to mention the risk of it's containing anaerobic pathogens and alcohols) suggests that compost extracts are not worth the effort. We don't consider it safe or advisable to use them.
Manure tea, created by suspending a bag of manure in water for several weeks, is also anaerobic. Using manure is asking fro pathogenic problems and, especially under anaerobic conditions, virtually assures the presence of E.coli. We want the beneficial microbes to be working in our soils and to get these; you have to keep things aerobic.


Modern compost tea

Modern compost teas, on the other hand, are aerobic mixtures. If the tea is properly made it is a concentrate of beneficial, aerobic microbes. The bacterial population, for example, grows from 1 billion in a teaspoon of compost to 4 billion a teaspoon of an actively aerated compost tea. These teas are made by adding compost (and some extra nutrients to feed its microbes) to dechlorinated water and aerating the mix for one or two days. It is this mixing, or active aeration that brings old-fashioned anaerobic compost teas into the modern era; it is also what keeps these compost teas aerobic, and thus safe. The air supply must be sufficient to keep the tea aerobic throughout the entire process.
It takes energy to separate microbes from compost. You know how much energy you have to use daily (or should) to remove another form of bacterial slim: plaque on your teeth. Bacterial slime in soils is just as strong. Consider, as well, that fungal hyphae grow not only on the surface of compost crumb but inside its nooks and crannies; you have to use energy to pull these strands off and out in addition to getting the bacteria "unglued." Of course, too much energetic action can kill these microbes. A brewer's action must be strong enough to tease out the microbes but not so strong that the microbes are killed once they are out of the compost and into the tea.


The brewer

More and more compost tea brewers are on the marker. These range from small, 5- to 20-gallon systems that can easily make enough tea to take care of a few acres (about 1.2 hectares) to commercial brewers capable of producing up to a thousand gallons or more of tea per brew. The Internet is a good place to look for compost tea brewers and compare them. Manufacturers should be able to show tests demonstrating that their machines can extract viable populations of fungi as well as bacteria. Only biological test will tell you the numbers. Insist on seeing one, and if they don't have one, don't buy the machine.
You can also make an actively aerated compost tea brewer. It is very easy and our suggestions for those just starting with teas. All you need is one of those ubiquitous five-gallon plastic buckets; add to this an aquarium air pump (the biggest you can afford) and air stone, and about 4 feet (1.2 meters) of plastic tubing to use with it. The better pumps have two air outlets; if you cannot get a double-outlet pump, use at least two single outlet pumps. Sufficient aeration is critical. Once your system is operation, you will know if you have enough air. If the tea smells good, things are fine. If it starts to smell bad, the tea is going anaerobic.
We learned in physics that the smaller the bubbles, the higher the surface to air ratio and thus more air exchange with the water, but when bubbles get too small, under 1 millimeter, they can cut up microbes. Aquarium air stones work well as long as you remember to keep them (and the plastic tubing that attaches them to the pump) clean.


Sitting and cleaning the brewer

Temperature is important when brewing compost teas. If it is too cold, microbial activity slows. If temperatures get too high, then the microbes are literally cooked or go dormant. Room temperature is ideal. Keep track of the water temperature. This is one of the variables you can adjust later, if need be, and a record of this information will be helpful to the lab testing your samples. If you cannot site your brewer in a warm place with steady temperatures, then a small, inexpensive aquarium heater might be needed; these come with automatic thermostats. If it is too hot where you make tea, you may have to consider "packing" your bucket with ice or occasionally adding ice to it to keep temperatures down.
Compost tea should be made away from direct sunlight because its ultra-violet rays kill microbes. And, since the proteins (worm bodies, primarily) in compost have a tendency to foam in the tea; make sure you keep your brewer in a spot that can tolerate some spillage.

It should be obvious but must be noted that it is important to clean up right away when making actively aerated compost teas. Bacterial slime is strong stuff and can clog the air holes in bubblers and tubing. This bioslime will appear in the strangest places. It will stick to the sides of the bucket and accumulate in the crevice at the bottom of the bucket. You may have to take apart hoses and fittings to clean them thoroughly. So, even before you use your tea, clean your system. If you get to it while it is still wet, you can usually wipe it off or "blow" it off with the force of water from a hose; at a minimum, flush it with water. Use a 3% hydrogen peroxide product or a solution of 5% baking soda to clean slime that has dried.


Ingredients

Actively aerated compost teas contain lots of bacteria, fungi, nematodes, and protozoa because that's what's in compost. What makes these teas such a good soil food web tool (besides the high concentration of microbes) is that you can tailor-make AACTs to feed plants according to their specific needs by adding certain nutrients (see Rule #10)? Use Rule #10, which applies equally to compost, mulches, and soil, when you make compost tea, and it evolves into Rule #11: by choosing the compost you begin with and what nutrients you add to it, you can make teas that are heavily fungal, bacterially dominated, or balanced. For many, the brewing process grows into a hobby in and of itself, not unlike making beer.
All recipes, however, start with the basic ingredients, the first being chlorine-free water. Rule #12 is very important: compost teas are very sensitive to chlorine and preservatives in the brewing water and ingredients. It is vitally important that none of the ingredients you use contain any preservatives. This makes sense. After all, these chemicals are intended to kill or discourage microbial life. If you are served by a water system that uses chlorine, you will need to fill your brewing container with water and run air bubbles through it for an hour or two. The chlorine will evaporate, making the water safe for microbes. Carbon filters and reverse osmosis water systems also work well to remove both chlorine and chloramines, and are particularly useful if you need large quantities of water. As a general rule, a carbon filter containing one cubic foot of carbon will filter four gallons of water a minute.
Next, you need to use good compost (forgive this redundancy: to us, all compost is good, or it isn't compost). Again, make sure there are no chemical remnants in it, and by all means give it the sniff test. If it doesn't smell good, it isn't good compost. Obviously, the best way to know is to have it tested. Avoid "almost compost," compost that hasn't finished the process or has gone stinky are anaerobic. Don't bother with compost that was allowed to overheat, killing beneficial microbes and reducing its soil food web. If you have a low diversity of microbes in your compost, you will have low diversity in your tea.
Vermicastings are a good substitute for compost. These are full of benefiticial microbes and tend to be very bacterial (remember the role bacteria play inside the worm, digesting food), especially when they are fresh. For the initial five-gallon brew, you will need approximately four cups of either compost or vermicompost. You can use proportionately less compost the bigger the brew.
As for the extra ingredients, you can feed the microbial population while teas are brewing. Molasses (nonsulphured, so as not to kill the microbes) in powdered or liquid form, cane syrup, maple syrup, and fruit juices all feed bacteria in teas and increase their populations. Two tablespoons of any of these simple sugars in four or five gallons of water will help bacteria multiply and establish dominance. If you make a bigger brew, add more nutrients in the same proportion: the amount of all added nutrients will vary linearly as you increase the size of your brew. More complex sugars and fish emulsion are also good bacterial food, though both will also support some fungal growth.
To encourage fungal growth in compost teas, add kelp, humic and fulvic acids, and phosphate rock dusts, which not only provide the fungi with nutrient value but also give them surfaces to attach to while they grow. Ascophyllum nodosum is cold-weather kelp that can be purchased over the Internet, at garden centers, and even animal feed stores, where it is often sold as powdered algae. The pulps of fruits like oranges, blueberries, and apples will also help fungi grow in compost teas, as will aloe vera extract (without preservatives) and fish hydrolysate (which is essentially enzymatically digested ground-up fish bones and all). You can buy fish hydrolysate at some nurseries or make your own by adding papain (aka papaya peptidase) or kiwi (which also contains the appropriate enzymes) to a blend of fish to enzymatically digest the bones. Yuca and zeolites are also good fungal foods and do not support populations of bacteria.


Give fungi a head start

Many new to tea brewing become frustrated because it can be difficult to grow fungi in quantities sufficient to make a balanced tea, much less a fungally dominated one. This is because bacteria not only grow but multiply rapidly in tea for fungi to multiply in tea----they only grow bigger. The better way is to activate fungi in the compost prior to making tea, allowing populations to multiply before they are teased out of the compost and into the tea brew.
This activation is easily accomplished: several days before brewing the tea, mix the compost with simple proteins that serve as a good fungal food----such things as soybean meal, powdered malt, oatmeal, oat bran, or, best of all, powdered baby oatmeal. Thoroughly mix in one of these at the rate of three or four tablespoons per cup of compost. Make sure there is sufficient moister in the compost, which is to say a drop of moisture can be squeezed out of a fistful of it. Put the mixture in a container, and place the container in a warm, dark place. A seed-germinating mat, placed beneath the container, works great to provide the proper heat.
After about three days at 80F (27C), the fungi in your compost, if you had sufficient numbers of them in the first instance, will have grown, and their invisible threads merged into a network of visible mycelia. The compost look like Santa Clause's beard, covered with long, white, fluffy strands. In a few days, there will be so many fungal threads; the entire container of compost will be glued together.


Teatime

Once you turn your machine on, the bubbles agitate the compost and start peeling microbes off and out of it. Depending on the compost and the nutrients, you may experience a bit of foaming; this can signal that worm protein is being released from the compost----a good thing. You can add mycorrhizal fungi at the very end of the brew cycle. If you put spores into the tea while it is being made, either they will be destroyed or the fungal hyphae they produce will be destroyed---they are both very fragile; also, since mycorrhizal fungi live off of root exudates, they and the tea must reach plant roots quickly.
It takes between 24 and 36 hours to develop a good tea using our simple bucket bubbler; some commercial brewers, with their high-energy systems, make tea in 12 hours. In any case, during the course of brewing, tea turns coffee-brown, another favorable sign: the humates in the compost are being teased out into the tea. The temperature of the brew may also increase a few degrees, a result of increased metabolic activity. The best part is the smell. The smell of a compost tea, especially when molasses is used as a nutrient, is a healthy, sweet, earth smell.
Compost tea has a very short shelf life. So many microbes now populate the brew that they quickly deplete the nutrients and start eating each other; more important, they are using up all the oxygen. If you are offended by the odor of a tea, it has probably gone anaerobic and should be discarded; do not toss it on your plants, for obvious reasons. It is best to use compost tea within four hours of manufacture, though it will last, diminishing in populations, for about three to five days if kept refrigerated or if you continue to bubble air through it.
After you have had some experience making teas, you may want to modify your machine in order to make better and better teas, meaning those that have higher numbers of microbes.


Application

Right at the outset we will tell you that you can never apply too much compost tea (our research shows no ill effects from unlimited applications). It doesn't burn plant roots or leaves, and the microbiology in the tea will adjust to the nutrients available at the site. Repeatedly applying compost tea will only help increase diversity of the microbial populations in your soils.
Once the tea is ready, apply it as a soil drench using a cup, a plastic watering can (bacteria can impact the zinc in metal containers), or (if the tea has been strained) a hand pump sprayer. Since compost tea will "stick" to leaf surfaces, you can inoculate leaves with foliar spray of beneficial microbes. To be effective as a foliar spray, the tea must cover 70% of the leaf surface. Cover both sides of the leaves. When applying compost teas to soils, drench your plants and the area around them with the tea. You cannot overdo it.
And don't forget the sun: ultraviolet rays kill microbes. If you live in southern latitudes, you will want to apply before 10 am or after 3 pm, when UV rays are weakest, even on a cloudy day. There is no microbial sun block lotion. It can take 15 to 30 minutes for bacteria or fungal hyphae to attach themselves to a leaf (where they can get some protection) ---far too long a period to be exposed to the sun's rays. Alternatively, spray with a drop diameter of at least 1 millimeter; with that much water, bacteria can develop enough slime to establish themselves before the water even evaporates. UV rays can also negatively affect the microbiology in soil drenches, but you can be a bit more relaxed a bit out the timing of these since the microbes sink into the soil and leaf duff layer almost immediately.
Remember, you are dealing with living organisms here. The microbes you carefully cultivated and nurtured in your tea are very much alive and require gentle treatment. Sprayers must not exceed pressures of 70 pounds, and the velocity of the spray should be slow. Either stand back or turn the spray head up, so that the tea drops "parachute" down to the surfaces to be covered; there should be no forceful "splatting" of the tea onto the soil or lawn or plants, as this is what will sometimes kill the plant, not the pressure of the tank. Electrostatic sprayers, incidentally, may destroy microbes by putting the wrong charge on them, so test the tea from such a sprayer before using one.
It is possible to use a hand pump sprayer if you strain your tea, but you must take care not to strain the microbes out. The mesh of any "compost sock" should be at least 400 micrometers, which is big enough to let fungi and nematodes flow through but will keep out particulate matter that will clog conventional sprayers. Alternatively, you can decant a tea solution by letting it sit for 15 minutes after the aeration is stopped. This gets rid of a lot of the bits and pieces; the bad news is that often the amount of fungi in the ea is diminished.
You will be better off if you invest in a concrete sprayer, only with fewer bends, larger orifices, and nozzles that support bigger particles. For prices and availability, check with your local builders supply store, concrete contractor, concrete supply store, or sand and gravel company. A gasoline backpack mist sprayer is also appropriate, especially for a large yard. A great way to do a lawn is to use a traveling sprinkler with a fertilizer dispenser feeding tea into the water stream.
Whether sprayed or poured, the microbes in the tea will establish themselves, grow, breed, attract predators, eat and be eaten, or go dormant. They create protective barriers around the roots and release nutrients when they die. They create and improve soil structure. They make protective barriers on leaves and compete with bad guys there as well.
Compost teas go to work immediately, and for this reason it is important that the tea applied be a good one, full of beneficial organisms, not diseases or pathogens. There is little room or tolerance for a poorly made tea. If you are not up to the job yourself, you can purchase AACTs from an ever-growing number of commercial nurseries and garden center; some companies not only make but will apply compost teas for you. In either case, it is still advisable to ask for test to see how the tea measures up and, of course, don't be afraid to give commercially made teas the smell test before buying or applying them. They may have started out fine but hone anaerobic before sale.
you can apply AACTs as often as you like, but how often you need to apply them (especially if you are paying for them) depends, as you can imagine, on the status of the soil food web organisms in the areas concerned. First-timers should get a base reading on microbiology and arthropod counts before "taking up" this very effective tool. As your soil food web becomes healthier, you'll need to apply tea less often. Thus, if your yard has had applications of chemical fertilizers for years, you should put down compost tea every other week for 3 months to establish a healthy soil food web population. Then you can start applying tea once every month for a season and finally three times a year.
How much compost tea should you apply in any given session? For two years one of us used about 60 gallons a week on a quarter-acre lot with positive results. The general rule, however, is to apply five gallons of compost tea per acre as a soil drench, ten gallons if you are going to spray leaves as well. It is fine to dilute the tea: just make sure there were five gallons when you started. When you are more experienced, you can match the amount of tea you apply with soil test and tea test to achieve specific fungal or bacterial ratios.


Timing

When it comes to out competing disease organisms in the soil or phyllosphere, fungally dominated teas have been used to prevent and suppress the growth of powdery mildew (Erysiphe graminis on turf, Phytophthora spp. on rhododendrons), downy mildew (Sclerophthora spp.), take-all (Gaeumannomyces spp.), gray snow mold (Typhula spp.), pink snow mold (Microdochium spp.), rusts (Puccinia spp.), and fairly rings (all sorts of fungi).
Bacterially dominated teas have been useful in out competing pathogens in mild cases of dollar spot, necrotic ring spot, yellow patch, leaf spots, pink patch, and stripe smut. Insects too succumb to the effects of compost teas, specifically weevils, grubs, cut-worms, and chafers; several reports attest to negative impacts on whiteflies, fire ants, and scale.
At the first sign of disease or insect infestations on any of your plants, apply teas and repeat in five to seven days...you should also apply teas in advance to prevent breakouts.
Compost teas are a veritable liquid soil food web. Instead of lugging around wheelbarrows of compost, consider compost teas, a concentration of the same microbiology. When you use them, you are really teaming with microbes.


Annuals and vegetables prefer bacterially dominated soils

What are the soils in your vegetable and flower beds like? Look for earthworms. They survive by eating protozoa and bacteria, and, as with lawns, if you have lots of earthworms and earthworm castings in your soils, then you probably have bacterially dominated soils with plenty of nitrates, which are what most vegetables and annuals prefer (remember Rule #2). Set up the Berlese funnel and see what kinds of micro arthropods are roaming the soils. You want to see lots of bacteria- eating mites and good diversity of animals. Measure your soil's pH in the rhizosphere. If it is decidedly alkaline, you most probably have a bacterial dominance. Similarly, an acidic reading means you have fungi and probably fungal dominance. Finally, get your soils tested for its microbiology; this is the best way to know what is missing, if anything. Sure, an NPK test won't hurt, but it is really the biology you need to know about.


No One Ever Fertilized an Old Growth Forest

Does the soil food web really support plants? Will it work in your yard and gardens? Just to give you confidence and to encourage you to use what you have learned, we point you in the direction of the nearest forest. Or simply close your eyes and visualize any wooded area you remember visiting. You can almost hear a stream nearby, the wind running through the leaves. It is beautiful, majestic----and no one ever fertilized any of the plants there. Not one single time. How can this be??? You know the answer. The beautiful plants in these beautiful areas are completely controlled by the soil food webs in which they live.
It often comes as a surprise when gardeners so reflect. Only then does the full force of the realization hit: every single plant you are seeing produces exudates and attracts microbiology to its rhizosphere. This community in turn attracts micro- and macro arthropods, worms, mollusks, and the rest of a complete soil food web. It is a natural system, and it operates just fine without interference from man-made fertilizers, herbicides, and pesticides. Tall oaks grow from small acorns with no blue powders to feed them or nasty smelling sprays to protect them. Plants flourish nonetheless, thanks to bacteria, fungi, protozoa, nematodes, and the rest of the soil food web gang.
You have been introduced to the basic science of soil food webs. You know how the system works, and you have been exposed to its benefits. With microbiology returned to your garden, soil structure improves. Mycorrhizal fungi will help your lawn, trees, shrubs, perennials, annuals, and veggies get the nutrients they need. Pathogens face fierce competition. Plants get more of the kind of nitrogen they prefer. Water drainage and retention are improved. Pollutants are decayed. Food tastes better. Flowers look better. Trees are less stressed. And you don't have to work so hard; you will have lots of helpers. Best of all, you won't have to worry about the affects of chemicals on you and your family, pets, or friends.
Remember: no one ever fertilized an old growth forest. They didn't have to. You have been given the rules to garden using the soil food web. There are not many of them. What are you waiting for? Start teaming with microbes and get that biology into your soils and working for you. Gardening with the soil food web is the natural way to grow.

[ame]http://www.youtube.com/watch?v=3WXBGonPAu0&feature=player_embedded[/ame] [ame]http://www.youtube.com/watch?v=O25LugxZUFI&feature=related[/ame] [ame]http://www.youtube.com/watch?v=FtbvlQBu7WY&feature=related[/ame]

EDIT....just found the torrent download for the book, read it for free (...be sure to click the right download tab @ lower page ) >>> Teaming with Microbes - A Gardeners Guide to the Soil Food Web (organic) - FREE Torrent Download - ExtraTorrent.com The World's Largest BitTorrent System

 

...very true!

 

....thankx paw paw! Yeah, I was doing some kinetics there, hahahahaha, some can just hear it and learn it, some just read it, I have to write/type it to remember it!...wtf? ...figured GS would like to possess the golden words. Also, in the book, they linked a site >>>>> Soil Foodweb ....more good reading!

 

...true, true!
...you da man LD(2?) ...why the new profile?

 

....just found the torrent download for the book, read it for free (...be sure to click the right download tab @ lower page ) >>> Teaming with Microbes - A Gardeners Guide to the Soil Food Web (organic) - FREE Torrent Download - ExtraTorrent.com The World's Largest BitTorrent System

 

[ame]http://www.youtube.com/watch?v=zUKeTz70GAY[/ame]

 

[ame=http://www.youtube.com/watch?v=a-JqApyMaP4&feature=player_embedded]YouTube - Compost made Easy![/ame]

 

...no salts, no preservatives, no chlorine. Those are the rules....I would not use soy sauce.
...have you read the book "Teaming with Microbes" link in my sig? Plenty info there.

 

...something to know about organics sold in bottles that are liquid form.


Air or no air



There are two main groups of bacteria. The first, anaerobic bacteria are able to live in the absence of oxygen; indeed, mostcannot live in its presence. The bacterial Clostridium, for example, does not need oxygen to survive and can invade and destroy the inside soft tissue of decaying matter. By-products of anaerobic decay include hydrogen sulfide (think rotten eggs), butyric acid (think vomit), ammonia, and vinegar. The notorious Escherichia coli (E.coli) and other bacteria normally found in the mammalian gastrointestinal tract meaning they can live in aerobic conditions if they must but prefer anaerobic environments.

Most gardeners have smelled by-products of anaerobic decomposition, perhaps ingarden but certainly in the refrigerator. These are smells to remember when composting and gardening with soil foodweb because anaerobic conditions foster pathogenic bacteria and, worse, killoff beneficial aerobic bacteria, the other major group of bacteria: those that require air.

While some facultative aerobic bacteria are able to live in anaerobic conditions if they must, most cannot. Aerobic bacteria are not normally known to cause bad smells. In fact, the actinomycetes (of order Actinomycetales, specifically thebacterial genus Streptomyces) produce enzymes that include volatile chemicals that give soil its clean, fresh, earthy aroma. Anyone who has gardened recognizes this smell, the smell of “good soil.”

Actinomhyctesare different from other soil bacteria: they actually grow filaments, almost like fungal hyphae. Some scientists believe Streptomyces species use their branching filaments to connect soil particles so they, along with the soil particles, become too big to be eaten by their natural predators, the protozoan ciliates, which would engulf and ingest them. Actinomycetes are particularly adept at decaying cellulose and chitin---two difficult –to- digest (“brown”) carbon compounds, the former found in plant wall cells and latter in fungal cell walls and in arthropod shells. These are not normal foods of other bacteria. Actinomycetesare also adapted to live in a wider range of pH than other bacteria, from acidic to alkaline.

 

What Is the Soil Food Web and Why Should Gardeners Care?



Given its vital importance to our hobby, it is amazing that most of us don’t venture beyond the understanding that good soil supports plant life, and port soil doesn’t. You’ve undoubtedly seen worms in good soil,and unless you habitually use pesticides, you should have come across othersoil life: centipedes, springtails,ants, slugs, ladybird beetle larvae, and more. Most of this life is on the surface, in the first 4 inches (10centimeters); come soil microbes have even been discovered living comfortablyan incredible two miles beneath thesurface. Good soil, however, is not justa few animals. Good soil is absolutely teeming with life, yet seldom does the realization that this is so engender a reaction of satisfaction.

In addition to all the living organisms you can see in garden soils (for example, there are upto 50 earthworms in a square foot [0.09 square meters] of good soil); there is a whole world of soil organisms that you cannot see unless you use sophisticated and expensive optics. Only then do the tiny,microscopic organisms----bacteria, fungi, protozoa, nematodes----appear, and in numbers that are nothing less than staggering. A mere teaspoon of good garden soil, as measured by microbial geneticists, contains a billion invisiblebacteria, several yards of equally invisible fungal hyphae, several thousand protozoa, and a few dozen nematodes.

The common denominator of all soil life is the every organism needs energy to survive. While a few bacteria, known as chemo synthesizers, derive energy from sulfur, nitrogen, or even iron compounds, the rest have to eat something containing carbon in order to get the energy they need to sustain life. Carbon may come from organic material supplied by plants, waste products produced by other organisms, or the bodies of other organisms. The first order of business of all soil life is obtaining carbon to fuel metabolism----it is an eat-and-be-eaten world, in and on soil.

Do you remember the children’s song about an old lady who accidentally swallowed a fly? She then swallows a spider (that wriggled and jiggled and tickled insideher) to catch the fly, and then a bird to catch the spider, and so on, until she eats a horse and dies (of course!). If you made a diagram of who was expected to eat whom, starting with the fly and ending with the improbable horse, you would have what is known as a food chain.

Most organisms eat more than one kind of prey, so if you make a diagram of who eats whom in and on the soil, the straight-line food chain instead becomes a series of food chains linked and cross-linked to each other, creation a web of foodchains, or a soil food web. Each soil environment has a different set of organisms and thus a different soil foodweb.

This is the simple, graphical definition of a soil food web, though as you can imagine, this and other diagrams represent complex and highly organized sets of interactions, relationships, and chemical and physical processes. The story each tells, however, is a simple one and always starts with the plant.



Plants are in control

Most gardeners think of plants as only taking up nutrients through root systems and feeding the leaves. Few realize that a great deal of energy that results from photosynthesis in the leaves is actually used by plants to produce chemicals they secrete through their roots. These secretions are known as exudates. A good analogy is perspiration, a human’s exudates.

Root exudates are in the form of carbohydrates (including sugars) and proteins. Amazingly, their presence wakes up, attracts, and grows specific beneficial bacteria and fungi living in the soil that subsist on these exudates and the cellular material sloughed off as the plant’s root tips grow. All this secretion of exudates and sloughing – off of cells takes place inthe rhizosphere, a zone immediately around the roots, extending out about a tenth of an inch, or a couple of millimeters. The rhizosphere, which can look like a jelly or jam under the electron microscope, contains a constantly changing mix of soil organisms,including bacteria, fungi, nematodes, protozoa, and even larger organisms. All this “life” competes for the exudates inthe rhizosphere, or its water or mineral content.

At the bottom of the soil food web are bacteria and fungi, which are attracted to and consume plant root exudates. In turn, they attract and are eaten by bigger microbes, specifically nematodes and protozoa (remember the amoebae,paramecia, flagellates, and ciliates you should have studied in biology?), who eat bacteria and fungi (primarily for carbon) to fuel their metabolic functions. Anything they don’t need is excreted as wastes, which plant roots are readily able to absorb asnutrients. How convenient that this production of plant nutrients takes place right in the rhizosphere, the site of root-nutrient absorption.

At the center of any viable soil food web areplants. Plants control the food web for their own benefit, an amazing fact that is too little understood and surely not appreciated by gardeners who are constantly interfering with Nature’ssystem. Studies indicate that individual plants can control the numbers and the different kinds of fungi and bacteria attracted to the rhizosphere by the exudates they produce. During different times of the growing season,populations of rhizosphere bacteria and fungi wax and wane, depending on the nutrient needs of the plant and the exudates it produces.

Soil bacteria and fungi are like small bags of fertilizer, retaining in their bodies nitrogen and other nutrients they gain from root exudates and other organic matter (such as those sloughed-off root-tip cells). Carrying on the analogy, soil protozoa and nematodes act as “fertilizer spreaders” by releasing the nutrients locked up in the bacteria and fungi “fertilizer bags.” The nematodes and protozoa in the soil come along and eat the bacteria and fungi in the rhizosphere. They digest what they need to survive and excrete excess carbon and other nutrients as waste.

Left to their own devices, then, plants produce exudates that attract fungi and bacteria (and, ultimately, nematodes and protozoa); their survival depends on the interplay between these microbes. It is a completely natural system, the very same one that has fueled plants since they evolved. Soil life provides the nutrients needed for plant life, and plants initiate and fuel the cycle by producing exudates.

 

Cation exchange capacity

All tiny particles, not just humus, carry electrical charges. These particles are called ions. Ions with a positive (+) charge are called cations and negatively charged (-) ones, anions. Positively charged particles are electrically attached to negatively charged particles. This is exactly what happens when opposite ends of magnets attract each other. When a positively changed cation attaches itself to a negatively charged anion, the cation is “absorbed” by the anion. Even microorganisms in the soil are small enough to carry and be influenced by electrical charges.
Sand particles are too large to carry electrical charges, but both clay and humus particles are small enough to have lots of negatively charged anions that attract positively charged cations. The cations that are absorbed by clay and humus include calcium (Ca++), potassium (K+), sodium (Na+), magnesium (Mg++), iron (Fe+), ammonium (NH4+), and hydrogen (H+). These are all major plant nutrients, and they are held in the soil by two components of good soil. The attraction of these cations to the clay and humus particles is so strong that when a solution containing them comes into contact, the attraction is satiated and only about 1% of the cation nutrients remains in solution.
There are anions in soil as well. These include chloride (Cl-), nitrate (NO3-), sulfate (SO4-), and phosphate (PO4-) ----all plant nutrients. Unfortunately, soil anions are repelled by the negative charge on clay and humus particles and therefore stay in solution instead of being absorbed. These plant nutrients are often missing from garden soils, as they are easily leached away in the soil solution when it rains or soil is watered: nothing is holding them on to soil surfaces.
Why does this matter? The surfaces of root hairs have their own electrical charges. When a root hair enters the soil, it can exchange its own cations for those attached to clay or humus particles and then absorb the cation nutrient involved. Roots use hydrogen cations (H+) as their exchange currency, giving up one hydrogen cation for every cation nutrient absorbed. This keeps the balance of charges equal. This is how plants “eat.”
The place where the exchange of a cation occurs is known as a cation exchange site, and the number of these exchange sites measures the capacity of the soil to hold nutrients, or the cation exchange capacity (CEC). A soil's CEC is simply the sum of positively changed nutrient replacements that it can absorb per unit weight or volume. CEC is measured in milligram equivalents per 100 grams (meq/100g). What the gardener needs to know is that the higher the CEC number, the more nutrients a soil can hold and therefore, the better it is for growing plants. The higher the CEC, the more fertile the soil. You can order a CEC test to be run by a professional soil lab.
The CEC of soil depends, in part, on its texture. Sand and silt have low CECs because these particles are too big to be influenced by an electrical change and hold nutrients. Clay and organic particles impart a high CEC to soils because they do carry lots of electrical charges: the more humus and, to a point, clay present in soils, the more nutrients can be stored in the soil, which is why gardeners seek more organic in their soils.
There are limits to a good thing. Don't forget that clay particles are extremely small; too much clay and too little humus results in a high CEC but little air in the soil, because the pore space is too small and cut off by the clay's platy structure. Such soil has good CEC alone; you have to know the soil texture and mixture.

 

Soil pH

Most of us have a basic understanding of pH as a way to measure liquids to see if they are acid or not. On a scale of 1 to 14, a pH of 1 is very acidic and a pH of 14 is very alkaline (or basic), the opposite of acidic. The pH tells the concentration of hydrogen ions (H+, a cation) in the solution being measured. If you have relatively few hydrogen ions compared to the rest of what is in solution, the pH is high and the solution is alkaline. Similarly, if you have a lot of hydrogen ions in solution, then you have a solution with a low pH that is acidic.
As a gardener, you (fortunately) don't need to know much more about pH. You do need to understand, however, that every time a plant root tips exchanges a hydrogen cation for a nutrient cation, the concentration of hydrogen ions in the solution increases. As the concentration of H+ goes up, the pH goes down---the soil is increasingly acidic. Things usually balance out, however, because root surfaces also take up negatively charged anions, using hydroxyl (OH-) anions as the medium of exchange. Adding OH- to the solution raises the pH because it lowers the concentration of H+ ions. Fungi and bacteria are small enough to have cations and anions on their surfaces, electrically holding or releasing the mineral nutrients they take in from decomposition in the soil. This, too, has an impact on the pH of the soil.
Why is pH a consideration when we talk about the soil food web? The pH created by nutrient-ion exchanges influences what types of microorganisms live in the soil. This can either encourage or discourage nitrification and other biological activities that affect how plants grow. As important, each plant has an optimum soil pH. This has more to do with the need of certain fungi and bacteria important to those plants to thrive in a certain pH than it does with the chemistry of pH.
Knowing your soil's pH is useful in determining what you want to put into your soil, if anything, to support specific types of soil food webs. And knowing the pH in the rhizosphere helps determine if any adjustments should be made to help plant growth.