Compost Explained

Composting Explained©


By Hugh Lovel


On a recent trip to Japan where I visited several organic farms as well as a golf course I noted that no matter how good their other practices none were composting well enough. All omitted clay from their compost mixtures. The same is commonly true on organic farms elsewhere, though I know of cases—most of them biodynamic operations—in Europe, India, the USA, Australia and New Zealand where composting is excellent.

My research shows that organic farming pioneer, Sir Albert Howard, (1873-1947), advocated soil, a good source of clay, as part of his compost mix. In my own case, one of the oldest and most experienced compost makers I’ve known is Fletcher Sims, who started composting on the Texas High Plains shortly after World War II—in which this pint sized Texan was a B-17 tail gunner in the old Army Air Corps. One of the secrets of excellent compost Fletcher shared with me was the incorporation of somewhere in the vicinity of 10% clay, either as soil or as rock powders that would make good clays. Fletcher also used compost inoculants either made with biodynamic preparations or using microbes derived from biodynamic preparations. And he developed world class compost turning machinery for aeration and moisture control.




I realize most growers think of compost as a means of recycling nitrogen, phosphorous and potassium (NPK) and they tend to measure compost quality in terms of its NPK analysis—which would be diluted if clay were added. Since organic agriculture was a reaction against the simple minded abuses of chemical agriculture, it adopted a natural and far more complex approach to the NPK mind-set, nevertheless retaining the belief that soluble N, P and K were essential to robust growth and high production. The difference was they replaced the miracle grow mentality—that the soil was there to hold the plant up and nutrients should be supplied in soluble form—with the use of crop rotations, lime, gypsum and other rock dusts along with microbial inoculants, composts, trace minerals, and organic carbon concentrates such as kelp, fulvic and humic acids.

On the other hand, Brazilian soil scientist, Ana Primavesi, pointed out in her brilliant rebuttal of the NPK mindset—which she called the Nutrient Quantity Concept or NQC—that basic agricultural research went awry back in the mid nineteenth century by analysing plants for their chemical components and then analysing poorly performing soils to determine their deficiencies, which then could be addressed with soluble inputs. She suggested we should all along have examined thriving untouched natural soils, such as found in rain forest or grassland ecosystems, in order to determine what goes on in a naturally thriving soil. Interestingly these soils often show up on soluble soil analyses as being deficient in soluble N, P or K even though total soil analysis using strong acids shows these elements present in what are thought to be unavailable forms. Thus she argued a new approach—which she termed the Nutrient Access Concept or NAC—was required. The question she asked is what is so different about thriving natural ecosystems versus farmed soils?


NPK vs. Micro-organisms


The first thing that comes to mind is the tremendous diversity of species, and as far as the soil is concerned this boils down to extremely diverse, high populations of micro-organisms in the soil—fed, of course, by the recycling of vegetative matter from above. The most immediate way this occurs is from the nightly cycling of a wide array of carbon compounds by root exudation from a diversity of plant species, each feeding a different community of micro-organisms in its root zone. Of course, mono-cropping defeats this since large plantings of single species causes microbial diversity to crash, which is why multi-cropping and multi-species cover cropping are sorely needed. Diversity of crop species, however, is a topic for another day.

What comes to light out of all this is that composts should be thought of as a means of restoring micro-organism diversity to soils. In other words, composts are micro-organism inputs, not NPK inputs. The well-known soil microbiologist, Dr. Elaine Ingham, has been arguing this for years, and has set up laboratories in a number of countries for testing the levels and diversity of micro-organisms in soils and composts. And since truly good compost is such a rarity she has popularized the concept of compost tea brewing, which—when done successfully—can brew high populations of diverse soil microbes to be applied in liquid form repeatedly throughout a crop cycle for a fraction of the cost of applying mediocre composts at high enough rates to assure the numbers and diversity for sufficient release of a full array of nutrients.

Time after time it has been shown that repeated applications of well-brewed compost teas can shift the availability of nutrients in soils as long as these nutrients were present in the total test—or in the case of nitrogen if the right mix of nutrients is present for nitrogen fixation and microbial release. Aside from equipment design and microbial food source issues, the difficulty usually is finding a reliably robust and diverse starter culture for successful compost tea brewing. Essentially one must start with a good compost culture.


Where This Leads


Let’s step back a moment and review. Although organic farmers often think of composts as NPK inputs, composts should really be thought of as soil micro-organism boosters. Unfortunately, most composts are rather mediocre at doing this, although there are good ones which often enough are biodynamic. Why do biodynamic composts sometimes hit the bull’s eye? Is it just due to the biodynamic preparations? From my 30+ years experience with biodynamics I’d have to say no. Biodynamic preparations may help considerably, but I believe the real reason is that biodynamic growers have a greater tendency to understand that lime and silica stand at the poles of the mineral kingdom while clay mediates between the two. Remember, all the most successful compost makers—whether biodynamic or not—use some form of clay to make compost. Most biodynamic compost workshop leaders I’ve known emphasize the importance of clay in composting. Otherwise lime and silica do not have enough middle ground where interaction between these two polarities can occur. This seriously limits both the mineral and the microbial activity of the compost pile and tends to ensure the compost goes off toward one or the other extreme.


Biochemical Sequence


            Let’s look at this from the viewpoint of the biochemical sequence in plants, since this is also the basic requirement for good soil microbial activity. Clay, by definition, is aluminium silicate—which means that clay is the soil’s silica reservoir. But because aluminium doesn’t turn loose of silica all that readily, nature boosts silica release with a trace of boron—which is chemically akin to aluminium but far more reactive.

[Aluminium silicates come in a wide variety of forms from the simple Al2Si2O5∙OH4 of kaolin (the basis for porcelain) to a much more complex montmorillonite such as (Na,Ca)0.33(Al,Mg)2Si4O10(OH)2∙nH2O as would be found in rich black cracking soils with a cation exchange capacity of over 50.]

As far as plants are concerned silicon is the mineral basis for cell walls and connective tissues. Thus silicon provides containment and transport for all sap nutrients and protoplasm. In other words boron provides sap pressure and silicon provides the transport and containment system. Now we can we consider calcium, which American farm guru Gary Zimmer calls the trucker of all minerals. He’s right, of course, but let’s not forget that calcium trucks down a silicon highway. Calcium, assisted by molybdenum, is the basis of nitrogen fixation and amino acid chemistry. Nitrogen, allied with calcium in the form of amino acids, reacts with every other nutrient element, the most important being magnesium, which is the basis for chlorophyll and photosynthesis. Chlorophyll traps energy and shunts it via phosphorous into carbon structures, which go where potassium, the main electrolyte, carries them.

Thus the biochemical sequence for plants is B, Si, Ca, N, Mg, P, C, K. If, in making compost, we focus on N, P and K we leave out the beginning of this sequence. If we refuse to dilute the NPK content of our compost by adding clay we will make poverty compost that never gets its biochemistry rolling with B, Si and Ca. Thus the micro-organism content will not be up to the task of eating into the soil and fixing nitrogen—which tends to escape during the composting process.

When we look at compost as a micro-organism booster for digesting the soil so that sap pressure, transport, nitrogen fixation, photosynthesis and growth occur and our plants have plenty of root exudates to keep ramping up the microbial activity around their roots—then we need to put about 10% rich clay in our compost. This breeds high populations of the micro-organisms that eat soil. By putting clay—or a rock powder that makes a good clay—in our compost we can breed soil eating microbes in abundance.

            Fletcher Sims reckons that 2 to 3 tons per acre (5 to 7.5 tonnes per hectare) of this sort of well-made compost should be sufficient to boost the microbial activity of a decent soil enough for a robust crop of corn or potatoes—even though we are talking mono-crop farming. Contrast this with 10 to 20 tons per acre (25 to 50 tonnes per hectare) of mediocre compost being barely adequate—a five to one difference in application rates.

            The rest of the story can be worked out—keeping the pile aerated and moist, getting carbon to nitrogen ratios somewhere between 15 and 30 to 1, supplying major and minor nutrients to meet specific soil needs in appropriate forms and amounts, and using biodynamic preparations and/or compost inoculants. But understanding the importance of clay as the appropriate medium for culturing the micro-organisms most needed in turning soil into plant food can take a little more understanding than currently prevails—since this is non-existent in the NPK school of agriculture.


Some Pointers


            If the larger size earthworms are lacking in your piles, keep in mind that earthworms don’t have teeth, they have gizzards and they need grit. If your soil is lacking in grit, try freshly crushed rock powders that contain some coarser particles. An earthworm’s digestive tract is one of the best microbial culture vessels in the soil, and earthworms spread micro-organisms around pretty well, so it pays to give them what they need. Moreover, if your compost heap is too dry for earthworms, it’s too dry for the micro-organisms you need in your soil. Once earthworm activity slows down your compost is ready to spread, which makes them good indicators. Another indicator animal is ants. When they produce that formic acid smell that seems fresher than lemon they are doing their job of clearing toxicity from your compost.



Japan compost




This picture was taken at a model organic farm in Japan, but there was no clay in the compost. The concrete pad and covered sheds were necessary because of high rainfall, which is not usually a problem in Australia, but of course, it kept clay from getting into the compost.

Biochemical Sequence 3_1

In many ways the diversity and management of this farm was admirable, but the emphasis of nitrogen over silica due to the lack of clay in the compost shows in this patch of aquatic weeds in the rice. This particular weed can be symbiotic with rice, as it was where I saw it last year on a Japanese biodynamic farm. There growth was subdued, and its leaves were small, narrow and quite pointed—a sure sign of high silica in the soil.












buckwheat field

This scene, taken behind the composting shed, shows a paddock freshly sown in buckwheat—so called because it often takes only 8 weeks from planting to harvest and can follow wheat. Buckwheat rushes to flower by its third week, showing a particularly close relationship with phosphorous—as its roots host phosphorous solubilizing bacteria. This can be very helpful since wheat removes soluble phosphorous from the soil. Attention to good crop rotations was one of the admirable features of this farm. Also note the border areas with their lush diversity of species. The Japanese countryside can be spectacularly beautiful.



Here we see the turning of a small compost pile in Tolga, FNQ. The field broadcaster in the foreground (sometimes called a biodynamic tower) broadcasts the archetypal patterns of all the biodynamic preparations into the ethers around the clock and around the seasons. Biodynamic preparations are organizational in their action, and organization is the basis of life. Contrary to the belief of some, this is an organizational (etheric) device rather than a disorganizational device hooked up to the electric mains.




Here is adding a little fresh green matter from the garden to an otherwise slow pile.







compost water

Moisture is maintained by watering each layer as the compost is turned.







Finally, the finished pile, the tools used and a pile of finished compost that filtered through the pitchfork as the pile was turned. Tolga has heavy red clays so leached of their calcium that the magnesium left behind makes them 

tolgacomposthigh (1)extremely sticky when wet. Two years of gardening with the addition of soft rock phosphate, gypsum, boron humates and cover crops of maize with soybeans has changed this situation dramatically. The rich chocolate colour of the finished compost shows how the clay has absorbed the digested organic matter forming clay/humus complexes which are ideal for rich microbial diversity. The finished compost between the wheelbarrow and the stack will go on two beds being replanted, while the vegetation ripped out will return to the compost site with quite a bit of clay still sticking to its roots. The fresh material will be incorporated into a newly turned pile in thin layers.