Vermicast –Benefits & effects
The castings produced by worms act as a fertilizer. Worms have a very simple and unsophisticated digestive system, yet a proportion of insoluble minerals passing through it is converted into a plant-available form and cellulose is partially broken down. This digestive process is carried out by enzyme-producing bacteria and, when the castings are excreted, the bacteria are soil-benevolent and continue the work they carried out in the worms gut but now in the soil, i.e. converting minerals into plant-available soluble forms and breaking down cellulose to create humus.
Bacteria are also a rich storehouse of carbon-dioxide. By substantially increasing the level of vegetative matter in the soil, we will also increase the level of bacteria.
Vegetative matter is mainly carbon. If we push the soil content of vegetative matter from the present level of less than 1% up to 5%, and added to that the bacterial carbon that would be hosted by its presence, the 52 billion tonnes of carbon-dioxide locked up annually by plant life would be increased to maybe 150 billion tonnes.
NPK of vermicast
An NPK (nitrogen : phosphorus ; potassium) analysis of vermicast would show something like 1:1:1. Vermicast is produced from organic materials that have taken up minerals in exactly the ratio in which they were needed to produce and sustain growth. Therefore, the minerals are contained in castings in a natural balance such as is required by plants that usually have to seek them out but, in vermicast, they are readily available when they are needed. Significantly, in vermicast there is no excess of nitrates and phosphates, which are water-soluble and which, when applied in much higher concentrations in manufactured fertilizers, dissolve in run-off to pollute our land and waterways.
The great influencing factor on the NPK of castings is, of course, the organic matter ingested by the worms. Worms can’t manufacture any nutrients, only liberate them. If the ingested matter is nitrogen-rich, then so will be the castings; but if the matter is nitrogen-poor, then the castings will be also. However, the nutritional value of vermicast is not the point. The value of vermicast lies in the plant growth stimulants, the cationic exchange rate (see below) and the soil-benevolent biota.
One of the great difficulties in promoting the use of vermicast is the users will frequently request an analysis. Invariably, such an analysis is requested and made on the basis that the product is a fertiliser and not a biological stimulant. These analyses will detail the mineral content, not the important biological content. So, vermicast frequently fails the assessment of being able to provide essential minerals to soil – but that’s not what it’s about.
Applying vermicast instead of fertilizer to soil is like giving a hungry man a fishing line instead of a fish. Once the fish is eaten, it’s gone; but with a fishing line, he has the means and ability to access food far into the future. Vermicast is the fishing line, the bait and the skill all rolled into one! The biota introduced to the soil in vermicast (or its derivatives) can work away out of sight, releasing the minerals already there and trapping free nitrogen from the atmosphere.
Cationic exchange rate
An important, and often unrecognized, feature of vermicast is its cationic exchange rate. This is the rate at which the cationic soil trace elements can attach themselves to vermicast.
Everything in nature has an electrical charge. Some charges are positive (cations) and some are negative (anions). Organic vegetative matter is anionic and, because vermicast is a highly vegetative matter, it is strongly anionic. Most trace elements are cationic.
In simple terms, this means that trace elements are attracted to vermicast and readily bond to it in the same way that opposite poles of a magnet attract each other. Plants have a stronger pull than the vermicast and can therefore draw the trace elements away from the vermicast and into the roots.
Phosphorus (P) is one of the essential trace elements that are negatively charged, just like the organic matter. Phosphorus is therefore repelled by vegetative matter (like poles of a magnet repel each other) and will lie loosely in the soil. When rain comes, because the phosphorus is not bonded to anything, it is readily washed away. Phosphorus is often blamed for stimulating growth of water plants and upsetting the ecology of the fish environment. This is because, ultimately, loose unbonded phosphorus will be washed into a waterway; it can’t go anywhere else.
Soil decontamination – Heavy metals
Worms can also be used in soil decontamination. For example, on a site contaminated with heavy metals, worms can have a measurable effect in reducing the level of contamination. Much more research needs to be done on this subject. Trials conducted by different researchers, using different types of worms, have produced differing but encouraging results. In one trial, lead, zinc and calcium levels in contaminated soil were considerably reduced by worms (Ireland, 1975), and in another, worms extracted from two sites with differing concentrations of cadmium were found to have absorbed the same concentration of cadmium in their bodies (Martin & Coughtree, 1976). It seems likely that worms can absorb poisonous heavy metals from surrounding soil.