‘Humus’ is a very evocative word, conjuring pictures of rich, fertile soil and bounteous produce. It is defined by various dictionaries as ‘vegetable mould’, ‘the organic component of soil formed by the decomposition of organic matter’ and similar. The word derives from the Latin ‘humus’ (earth, soil) and ‘humi’ (on the ground). It is generally understood to mean the dark organic matter deriving from the breakdown of plant and animal matter. Humus is, however, a concept that is hard to define precisely, and is the source of much debate amongst soil scientists. Those who focus more on the chemistry of humus find that when they try to reduce it to its component parts, it is no longer humus and they lose sight of the whole. Those with a more biological focus generally agree that it is organic matter that has become stabilized, that it has many useful properties in soil and is more than the sum of its parts.
The Organisation of Soil
For millions of years nature has provided elements to plants through a wonderful coordinated orchestra of activity in the soil. If you fill your hands with good soil, you are holding billions of living organisms: insects, arachnids, worms, molluscs, microbes, protozoa, nematodes, fungi, algae, archaea and more. You are also holding hundreds of metres of plant roots and kilometres of fungal filaments together with many non-living catalysts, enzymes and co-enzymes.
How plants feed
The question of how plants feed is a highly complex one. There are many different pathways for plant nutrition. Firstly, plants make some of their own nutrition via photosynthesis. They convert water, sunlight and carbon dioxide into oxygen and simple sugars. Plant leaves can absorb nutrients directly (though this is abused by conventional growers using ‘foliar feeding’, the spraying of solutions of fertilisers on the leaves). Plant roots (primarily larger ‘water-uptake roots’) can absorb nutrients in solution from the soil water, primarily when water soluble fertilisers are used. Over 80% of terrestrial plants can form symbiotic relationships with mycorrhizal fungi whose fungal filaments enormously extend the reach of plant roots and help plants obtain required elements. Soil fungi also produce glomalin, a very important glycoprotein that plays a major role in soil binding, also holding large amounts of water and carbon dioxide. Most importantly, plant fine hair feeder roots can directly absorb water soluble nutrients held in colloidal humus, as directed by sun warmth. So many other factors are involved in plant nutrition (balances between different elements and cation exchange capacity to name just a few) that it is hard to gain a clear picture. From a purely practical viewpoint, the picture of plant feeding presented by Australian Biodynamic pioneer, Alex Podolinsky since the 1950s, as outlined below, represents one of the clearest and most applicable approaches for farmers.
Organic Matter and Colloidal Humus
One of the problems when discussing humus is the lack of precision in terms. ‘Humus’ is used quite broadly to describe various stages in the breakdown of organic matter. Not all humus is the same: it has been variously used to describe partially decomposed organic matter, soft dark leaf-mould and fully digested colloidal humus.
Organic matter comprises anything that has once lived. Nature is constantly at work breaking down organic matter and refining it towards the highest quality end-point, colloidal humus. Microbes, fungi, enzymes, co-enzymes, microfauna, macrofauna (particularly worms) and more, all play a specific role in converting organic matter into high quality colloidal humus. A colloid lies between a suspension (a heterogeneous mixture that doesn’t dissolve and the parts are able to separate) and a solution (a homogenous mixture in which one substance is dissolved in another and won’t separate). A colloid is a heterogeneous mixture, with particle sizes in between those of a suspension and a solution, and won’t separate. Examples of colloids include cheese, butter, jelly, worm castings, good quality compost and, of course, Biodynamic preparation ‘500’.
The characteristics of colloidal humus include: it is soft, moist and malleable (similar to soft putty); it contains soluble plant nutrients in a form available to plant roots but the nutrients are held within the colloid and won’t leach out; plant fine hair feeder roots can take in nutrients from soil colloidal humus pockets under the guidance of sun warmth; it can hold up to 75% of its volume as water, acting as a soil water reservoir. It is of fundamental importance in Biodynamic (and organic) agriculture, and one of our principal aims as Biodynamic farmers and gardeners is to build and maintain the soil colloidal humus ‘bank’.
Science and Humus
The increasing focus on scientific discovery from the 16th century delved into many subjects, terrestrial and cosmic. Not least of these was research on agricultural methods and plant nutrition. One of the leading agricultural researchers of the 19th century was Albrecht Thaer. In the early 1800s he established an agricultural college, later named the Royal Prussian Academy of Agriculture, on an extensive farm in Germany and carried out systematic research there for many years. Amongst his voluminous findings, perhaps the most important was that soil fertility depended on the level of soil humus, and that humus constituted plant food. He regarded humus as a biological-functional performance of the earth that should be viewed holistically. He further believed that inorganic salts were unnecessary for plant nutrition.
Despite their sound scientific basis, these findings were soon to be discarded – in the early 1840s, Justus von Liebig discovered that plant roots can only absorb elements in solution. Most scientists consequently discarded Thaer’s humus findings and the commercial production of water-soluble fertilisers began, phosphate being the first. Later in life, von Liebig recognised the importance of humus and lamented the overuse of water-soluble fertilisers, which he recognised pushed excessive and unhealthy plant growth, but was ignored by commercial interests.
In the 1960s, Alex Podolinsky, (who inspired and led the adoption of Biodynamic farming on hundreds of thousands of acres in Australia by the 1980s) began describing the process of natural plant feeding versus unnatural plant feeding in lectures to farmers worldwide. These ‘Biodynamic introductory lectures’ were later published in three volumes (Biodynamic Agriculture, Introductory Lectures, Vols. 1,2 and 3) starting in 1985, and have been translated into French, Italian, German, Russian, Chinese and other languages.
Podolinsky observed that plants have no independent warmth metabolism (in contrast to animals) and rely on sun warmth to stimulate nutrient uptake. Plants must take in water to replace that lost in transpiration. When plants are grown within nature’s organisation, nutrient uptake and water uptake are essentially separate processes: water uptake is mostly the function of the larger, more vertical, water uptake roots, and the soil water is relatively pure, containing little in the way of soluble elements, the soil life incorporating any free elements into soil colloidal humus. Nutrient uptake is primarily the role of the fine hair feeder roots, which take in nutrients from colloidal humus in the soil as directed by sun warmth. This ensures that the plant only takes what it needs at any time, and is metabolically balanced. By contrast, in a water-soluble-fed soil (whether the water-soluble elements derive from artificial fertiliser use, the application of raw manures or poorly made compost) the plant is forced to feed indiscriminately as it takes in water (because soluble elements are dissolved in the soil water), independent of the sun’s influence, thus becoming metabolically unbalanced. Plant cells become over-full of elements, leading to more water uptake (as the plant attempts to dilute the excess elements), bringing more unwanted elements. Plant cells become ‘blown up’ with unassimilated elements, affecting even the free movement of the stomata on the leaves and adversely impacting photosynthetic efficiency. Such plants, grown outside nature’s organisation, are often larger, coarser, darker in colour, look ‘heavy’ and lack upright expression, in contrast to the upright ‘upper plant expression’ of plants grown within nature’s organisation
In the 1950s, to answer some Victorian Agriculture Department scientists’ insistence that plant roots could only absorb certain parts of colloidal humus (eg humic acids), Podolinsky filled a glass jar with Biodynamic preparation 500 (pure colloidal humus) and buried it, open, 8cm below pasture in Spring. Six weeks later the entire humus substance had disappeared and had been fully replacedby white hair feeder roots.
Plants grown outside nature’s organisation, fed with water soluble elements, are poorly flavoured, lower in nutritional value, often carry unassimilated nitrates which can cause health problems, and have poor shelf life. And what does nature do with anything that is unbalanced? It sends insects and diseases to break it down. This is why conventional farmers and gardeners must often resort to chemical sprays to keep such unbalanced, over-blown plants alive and why conventional fruit is often starting to decompose by the time we get it home from the shop.
How can we develop colloidal humus in soil?
- The use of the Biodynamic soil preparations: one of the main advantages of Biodynamics over ordinary organic methods is the tremendous effectiveness of the Biodynamic preparations: the soil preparations 500 and 502-507 and the light metabolism enhancing preparation 501. Properly made 500 (which must be moist and colloidal) has been shown to greatly enhance microbial activity, humus formation and root growth, and, supported by general Biodynamic management, greatly improves soil structure, organic matter levels and many other soil characteristics. Prepared 500, made by the addition of the 6 Biodynamic compost preparations (502-507), has been shown to be significantly more effective in soil development than 500 by itself, and is the only form of 500 used on ‘Australian Demeter Biodynamic method’ farms throughout Australia, Europe and Asia in particular. On Alex Podolinsky’s Victorian dairy farm, using only the Biodynamic preparations and general Biodynamic management, the soil organic matter level in the top 100mm increased from 0.9% to 11.4% and at 1000mm, from 0 to 2.4%, in just the first 6 years!
- Biodynamic compost: properly made, this is 100% colloidal humus: pure, natural plant food. Although good colloidal compost can be made without the Biodynamic ‘compost preparations’, as Dr Ehrenfried Pfeiffer’s research demonstrated, not only does the composting process progress much more quickly with the preparations, but nutrient (particularly nitrogen) and microbial levels are also much higher (nitrogen 233% higher, microbial content 275% higher).
- Green manuring: the growing and working into the soil of species-diverse green manures (with 500 applications after sowing and after working in) develops high levels of colloidal humus in soils, and to a greater depth than compost applications due to the breakdown of the deeply penetrating roots after working in the green manure.
- Sheet composting: this includes rotational grazing, harrowing pastures after grazing by cattle, mowing or topping of pastures and green manuring.
Applying effective Biodynamic preparations, supported by overall Biodynamic management ensures healthy, biologically active soils, well supplied with colloidal humus: this in turn ensures healthy plants and animals, and the most beautifully flavoured, life-giving produce.
John Bradshaw is an Australian Biodynamic farmer and certification inspector, and publisher of Biodynamic Growing magazine (www.bdgrowing.com) from 2003-2019. His book, Biodynamic Farming Handbook: activating soil fertility for growing healthy food, Hawthorn Press, will be launched at the BDAA’s AGM at Darlington, UK, in October 2024: www.hawthornpress.com