Vermicast is produced from organic materials which have taken up minerals in exactly the ratio in which they were needed to produce and sustain growth. Therefore, the castings contain them in just exactly the natural balance. in which they are required by plants for vigorous healthy growth. The big difference is that plants usually have to seek them out, but in vermicast they are immediately and readily available. Significantly, in vermicast there is no excess of nitrates and phosphates, which are water-soluble and, when applied in much higher concentrations in manufactured Fertilisers, can be dissolved in run-off to pollute our land and waterways.
The great influencing factor on the NPK of castings is of course, the food ingested by the worms themselves. They can’t manufacture nutrients, only liberate them. If the food is nitrogen-rich, then so will be the castings. The reverse also applies.
A first step in forming stable soils is to promote the formation of aggregates.These are mineral granules bonded in such a way that arc resistant to water erosion and compaction. Aggregates important, because they assist in making soil stable and resistant to wind and water erosion. Stable aggregates are the foundation of sustainably fertile soils, providing the basis for farmers to make profits, long term, year after year Worm castings are formed of aggregates consisting of minute particles smaller than 2 microns (a micron is one thousandth of a metre — too small to imagine), which are bonded together by plea organic compounds called polysaccharides. Polysaccharides can take many forms. in this case they act as an organic glue.) They are also produced by the bacteria in the worm’s gut and, after excretion with the castings, the bacteria continue to feed the cellulose in the castings for energy so that they can produce more polysaccharides to strengthen the bonding of the particles a stable aggregate.
Aggregates demonstrate the earthworms’ role in helping to up the decomposition of cellulose in the soil. In passage through the gut, cellulose is not greatly digested, but rather broken down into minute particles so that the surface area is greatly increased. This means that microbial activity can be increased through access to this increased surface area, transforming soluble nitrogen into bacterial protein. Given food and oxygen, aerobic bacteria will double their population every twenty minutes and, in so doing, use nitrogen to form bodily protein. This stabilises the nitrogen, reducing the possibility of loss of soluble nitrogen by leaching. In turn, as these bacteria die off, the nitrogen becomes available to plants.
When deposited in the soil, the aggregates (casts), because of their high moisture content, offer a very hospitable microenvironment for a wide range of organisms. The interior of the cast will probably be anaerobic and the soil immediately surrounding it, aerobic. This means that there is an attractive meal for both aerobic and anaerobic bacteria, which together form an integral part of the soil ecosystem.
J_ N. Parle (A microbiological study of earthworm casts’) investigated bacterial growth in and around casts, finding that the total bacterial population was 100 times greater in freshly deposited castings than in the surrounding soil. Over a period of twenty days, Parle found a significant increase in the proportion of stabilised plant-available nitrogen, increasing from less than 4 per cent in fresh casts, to 35 per cent during this time. Other researchers (Jeanson, C., ‘Evolution de la matiere organique du sol sous !’action de Lumbritus hermit= Savigny (Oligochete Lumbricidae)’ and Czerwinski, Z., Jakubczyk, H. and Nowak, E., ‘Analysis of a sheep pasture ecosystem in the Pieniny Mountains (The Carpathians). XII. The effect of earthworms on the pasture soil.) concluded that most of the formation of humus in soils came about through a mixing of organic and inorganic materials in the worm’s gut.
M. B. Bouche (`Action de la faune sur les etats de la matiere organique dans les ecosystknes.) named the lining of an earthworm burrow, the drilosphere, and ascertained that the average thickness of this was 2 mm. A fellow researcher, T. Bhatnagar (`Lombriciens et humification: Un aspect nouveau de l’incorporation microbienne d’azote induite par les vets de terre!), found that about 40 per cent of the aerobic (and 13 per cent of anaerobic) nitrogen-fixing bacteria and 16 per cent of the denitriliers were contained within the drilosphere. The surface area of a worm burrow may not seem important but, when you also know that NI. B. Bouche (Strategies lombriciennes’) and A. Kretzschmar (`Quantification ecologique des gaieties de lombriciens, Techniques et premieres estimations’) found that the total area of burrow walls in pasture at CIteaux (France) amounted to five square metres per square metre of soil surface area, the importance of worms and their burrows to soil health takes on a new significance.
It is therefore easy to appreciate what is lost to the soil when worms are driven out. It seems to be more than coincidental that where farming practices involve frequent and deep ploughing, combined with the (often profligate) use of manufactured fertilisers, there has been a concurrent fall in both the size of the active worm population and aggregates in our agricultural lands. As recently as 1979, around Albany in Western Australia farmers spoke of worms hanging on cultivator tines like spaghetti This particular worm is called Megascolex imparacystis and grows to length of 30 cm. It is a deep-burrowing worm, going as deep a4metres with a burrow as big as 7 mm in diameter and extremely valuable for its work Now, few of these worms can be seen in these soils. This behavioural pattern is typical of Australian indigenous worms and, knowing this, it could not be expected that M. imparacystis would live in agriculturally prepared soils. But — what an incredible asset it would be if this was not the case!
Australian farmers are rightly considered to be among the worlds most efficient, yet, even in the better cropping areas, production rarely achieves 20 per cent of the rainfall potential,partly because much of the soil lacks aggregates and humus In simple terms, the soil can’t hold water. Wormless soil, lacking worming burrows and emus, drains poorly and, if there is a heavy rain, can become a g until the sun dries it out, at which time it may become hard d unyielding. If there were worms present in that same soil, it would have good drainage and water storage capabilities,distributing the moisture evenly throughout its structure.
As our knowledge of soil fertility, or rather the need to create the right conditions for plant growth increases, we have invariably developed techniques which have mimicked the work of earthworms — usually to their detriment. There is still a great deal about soil management that we do not know and the consequences of our errors abound. Surely, it is high time we acknowledged our shortcomings and learned to follow the lead of the master — the humble earthworm.
In 1881, Charles Darwin wrote that, ‘Earthworms prepare the ground in an excellent manner for the growth of fibrous-rooted plants and their seedlings of all kinds’. As our knowledge of earthworms and their role in soil formation and enrichment is accumulated — and remembered and used — the truth of this statement is continuously reinforced.