An old farmer once said to me “Used to be that the only test needed to see if the soil was good, was to walk on it. If it was soft and springy beneath your feet, it was good because it had worms in it. That land would be good land and would always grow good crops”. That’s a quote from my book “Organic Growing with Worms” and also from my earlier book “Earthworms in Australia” where it first appeared. It was a good statement way back then, it’s still a good statement and will always be good.But why ? Because it had worms in it ?

Why is worm populated soil ‘soft and springy’ and fertile ?? 
Most people have heard that worms eat their own weight daily - that’s ingest and excrete. Earth worms will do that, Compost worms will eat maybe half their weight each day. This is about earth worms, so let’s quickly look at the significance of that daily appetite.

Worms ‘eat’ their own weight daily because they are seeking their food and they have to extract this food from soil. Their preferred food is bacteria, yeasts, fungi, actinomycetes, and the like, all micro-organisms found in soil. The bacterial content of soil will be increased a thousand fold in its passage through a worm’s gut. This is an extraordinary example of symbiosis in that while bacteria are the preferred food of worms, they are also amazingly efficient incubators of more bacteria.

J.N. Parle discovered that Lumbricus terrestris commonly provided succour to around 474,075,000,000 soil benevolent bacteria. But since those days it has been discovered that because of improvements in laboratory techniques, bacteria numbers were under-reported by a factor of 50. Therefore Parle’s friend, L.terrestris, actually housed 23,703,750,000,000 active bacteria. (Just take note, that’s quadrillion !).

So, what’s the significance of bacteria in soil and what does a bacterial population have to do with soil fertility, and, how do worms figure here ???

When a worm ingests soil or organic matter, it is minimally processed and passes largely unchanged through the gut and deposited in the soil. The difference is that it has been ground small (worms have a crop like poultry) and loaded with bacteria. These bacteria eat. In fact they eat their heads off and because no animal can live in it’s own waste, and because bacteria can’t move about, they die. Some die inside the castings pellets, some outside in the soil. Bacteria are the richest form of Nitrogen on our planet and as they die, they give up their components, which are basically carbon and nitrogen.

The Nitrogen is taken by nitrifying bacteria and converted through NO2 (nitrite) into NO3 (nitrate) which is the form in which plants can absorb N into their systems. The Carbon is released into the soil as carbon dioxide CO2. Some of this is absorbed by the moisture in the soil and makes Carbonic Acid, H2CO3, with pH of around 6.8 – near neutral. (By this means an active worm population helps to regulate the pH of soil). The rest of the CO2 percolates up through the soil and breaks out where it is absorbed by the stomata on the under side of plant leaves. If there is N present – and we know there is – photosynthesis takes place and we have plant growth.

As worms eat and push their way through the soil, they leave burrows behind. As they go, they line these burrows with mucous which they exude through their skin.This mucous, which is very rich in nitrogen, hardens and is the reason the burrows are preserved. André Kretzschmar and Marcel Bouché researching worm populated soils in Europe determined that beneath every 1m2of surface soil, there was 5m2of burrow surface. They named this mucous hardened surface the drilosphere, and found it has an average thickness of 2mm.

Plants are not silly. When planted in a soil with a subsurface drilosphere, they will quickly send their roots along these easy to access channels. Rainfall will also use them to penetrate and infiltrate the soil and the drilosphere will dissolve, yielding up it’s N to the nitrogen-hungry plants, through the roots which are effectively lying in wait.

So, it’s a complicated interaction of micro and macro organisms which make up our fecund soils and none of it works without earthworms, which have been around for 650,000,000 years.