Benefits of Earthworms
- Earthworms burrow, consuming organic matter and soil and depositing urine and casts rich in beneficial microorganisms and available minerals. Worms even aid in the incorporation of fertiliser into the soil. They decompose organic matter and mix it throughout the soil. The burrows, earthworms create, help with soil aeration, water infiltration and drainage, as do the mucus secretions that bind soil particles into water stable aggregates.
- Earthworms speed up the decomposition of dead leaves and roots, and manure so that the nutrients contained are available sooner to growing plants. Worms combat root matting, a common limitation in grass growth.
- Worm casts are rich in colloidal humus with good water retention, soil structure properties and cation exchange capacity (ability to hold cation-exchange-sites nitrogen, calcium, magnesium etc. until utilised).
- Plant roots will often follow worm burrows, taking advantage of the trail of available minerals and the free space that facilitates root penetration. Conversely, dead roots of deep penetrating plants are fodder for worms, leaving channels, which increase soil drainage.
- Earthworms aid the spread of beneficial microorganisms by ingesting them or their spores and depositing them in casts. Microorganisms also multiply fast on the earthworm casts.
Significance of Earthworm Digestion
Earthworms can consume their weight in soil, water and minerals over a 24-hour period. It takes around 16 hours for this material to pass through the worm. During this time, the contents are subjected to a series of digestion processes.
1. The material is broken down into small pieces and sucked into the pharynx
2. It is acted upon by acid mucus and starch enzymes and sucked further into the oesophagus
3. The calciferous glands secrete calcium carbonate and it passes through to the crop
4. Crop conditions are made alkaline by the calcium secretions and a variety of enzymes and microorganism actions take place. It is then forced through to the gizzard.
5. Gizzard conditions are highly alkaline, helping break up of complex molecules and releasing some elements bound to other elements for example phosphorus to aluminium, there is a grinding action with small stones and mineral particles, as well as further enzymes and microorganism activity.
6. It is exposed to more enzyme and microorganism action while passing through the intestine.
7. After it is excreted as castings, bacteria continue to decompose some of the material.
Passage through the gut is a prolonged environment for enzyme and bacterial action. The breaking up of material increases its surface area and thus the accessibility for microorganism action. This activity warms the gut thus further speeding up decomposition.
It is the gut capacity of the soil that largely determines the rate of nutrient recycling in the soil – a good soil has lots of gut in terms of earthworms.
How to encourage Earthworms
All farms will benefit from increased worm numbers. The main factors affecting worm numbers are the level of calcium in soil solution, having adequate phosphorus levels, and in particular organic matter (food). Soil structure is important as worms do well in soils that are neither waterlogged nor too dry.
Earthworms promote a good soil and, conversely, a good soil promotes earthworms. The best way is to provide a balance of fertiliser based on a comprehensive soil test. Although lime will generally favor earthworms, it is best to know how much is desired and to keep the levels of other nutrients in a healthy balance. The resultant healthy plants and soil microorganism life will aid earthworm activity and numbers by providing food and good soil structure.
The main earthworm of interest is the grey field worm (Aporrectodea caliginosa). Pale pinkish to grey-pink to green in colour, the clitellum is from segment 31 to 33 and it has a spear shaped body. If your soil appears to be lacking in earthworms, there may still be sufficient numbers to create a healthy population under the right conditions – or eggs (capsules) could be lying dormant in the soil. An easy way to add earthworms is to take worm laden sods (30cm X 30cm X 10cm deep) and place them grass side down on the target pasture.
