Earthworm Effects on the Environment

 

Worm Digest Library

Ordinarily, normal farming procedures stipulates the use of chemical analysis to determine the basic nutrient needs for the planted crop. The element which is not in sufficient supply in the soil for a certain crop is then applied in the form of chemical fertilizer. The microbial life in the soil is given little consideration. In countries with climatic extremes, this has led to regarding soil as a mere holding media for crop plants.

 

The bio-organic farmer's priority is to increase the humus content in the soil. Rich in humus, the soil soaks up water and holds it more effectively, remains loose, aerated, and warm, and does not blow away or cake up. Further, it can better withstand the pressure of wheels and skid marks of farm machinery. Humus is a vast reservoir of all kinds of plant nutrients. It cannot be replaced by artificial means. In the living soil, the microbiological processes decompose crop residue and manure into plant nutrients and humus. They produce acid-sand release minerals for the benefit of the plants. Soil microbes have the ability to release P, K, Ca, Mg, Fe and S as well as other trace elements from various soil components.

Soil tests taken at Ebenrain showed that worm castings had, on average, twice as much potassium as normal soil, with a maximum of 4.5 times as much. Soil that passed through the earthworm contains approximately seven times as much nitrogen. The earthworm, working as a "fine drainage maker" not only improves the water and air circulation in the soil, but also mixes organic and mineral substances. They are then the smallest fertilizer factories which keep working at no cost to the farmer. The work is done on the spot without fossil fuels and no transportation is involved. However, as with all life phenomena in the soil, they are susceptible creatures and will not survive the application of poisons and aggressive chemical fertilizer.

There have been many studies on earthworms since Darwins observations. Most of these do not seem to agree over -How deep do earthworms dig? What is the length of burrows? etc.

We can be sure of one principle: If one digs and finds earthworms at 8 meters depth one can make a fair assumption that earthworms can be found at more than 8 meters depth, because of probability is very high that one did not dig out the deepest burrow there is.

To find the probabilities of burrow depth, we need a set of statistical data concerning burrows-and this is impractical because of the wide distribution we would find (because of the variety in soil, climate and species).

There are many Families of earthworms. The most widely represented is Lumbricidae with over 160 species(2-30cm[1-12in.],and the giant(up to 3 meters[10ft.]long )Australian Megascolecidae (Megascolides Australis)

Earthworms are generally feeding on organic matter that has started to decompose, mammalian dung and the deep burrowing species feed on soil (geophanous species),some even feed on nematodes. It has been found that nematode population may decrease by as much as 60% when earthworms are added to soil.

Also microbes play an important part of an earthworms diet, and earthworms even prefer organic matter with high concentrations of microbial life. Some researchers suggest that some microorganisms are essential to earthworms.

Water is a major necessity of earthworms as they contain about 80% water, by weight and loose about 15% per day. If moisture is not available they will dig deep into the soil to find it. The water uptake is related to surrounding temperature. The generalized limits to earthworm activity are form 273K (32 degrees F) for the lower limit to 303K (86 degreesF) for the upper temperature limit.

Generally we can see the effects of earthworms on the environment in three ways:

1) Biological - microbial concentration

2) Chemical - mineral availability, organic matter decomposition

3) Physical - Burrows (aeration. etc.) casts (mineral movement between horizons)

For sake of simplicity and because these three effects are so closely related let us consider the biological, chemical and physical effects of earthworms on their environment together.

The effects of earthworms on crop production vary widely from test to test. This not only because of species, crop and soil type but also the weather conditions at the time of test. For example, it has been shown that in orchards with high population of earthworms the trees have larger root systems by 40%. Yet yields are only 2% higher in these orchards. One would need to examine the stress resistance (yields in years of drought, ect.)of the orchards to find the true value of the earthworm effects on yields. Nevertheless yield increases as high as 900% have been observed on clover and 100% on wheat.

Often roots follow the burrows and feed on the more available nutrients in the immediate vicinity (within 2mm). An amazing fact is that roots often seek out the earthworm casts. This happens even if the roots have to grow upward! The reason for this is that the earthworms (or the microbes present in their gut) have concentrated high amounts of growth factors and vitamins into the casts.

The burrowing of earthworms helps bring up minerals to the A horizon from the B and C horizons. At the same time the lower horizons get enriched with the organic matter from the upper A and O horizon (see Soil Layers).This intermixing plus the increase of oxygen and water penetration to the lower horizons increases the depth of the top soil.

As much as a 2cm (1 inch) thick layer of subsoil may be brought to the surface per year by the burrowing of earthworms.

Another effect on the environment is that the casts are always more neutral (closer to pH 7) then the surrounding soil. This helps neutralize the acids or alkali that may be present in the soil thereby optimizing the pH for the root development of majority of cultivated plants.

A mucosal substance rich in proteins lines the wall of the burrows. This substance in turn serves as energy source for microbes. The concentration of nitrifying microbes has been observed to be about 40% higher in the burrows then in the rest of the soil.

This means that where there are earthworms there is good soil. For that reason, the earthworm is an ideal tool with which to measure the quality of the soil. An Ebenrain "rule of the fist" is: When plowing if you can count 80 earthworms for every 10 steps in the furrow, then the soil is good."

The important part of organic matter is its decomposition process. Ideally the first part of decomposition is carried out apart from the soil (pile composting).

As the organic matter is added to the soil the decomposition will yield valuable nutrients to the soil(mineralization), these are in available form and are used by the plants. Clay plays an important roll as its layers provide spaces for microorganisms to function. Good structure in the soil provides the growing plants with needed nutrients and makes for a fast turnover of organic matter.

The other part of decomposition yields humus and in combining humic acids, with clay yields stable humus. This part of the soil is relatively static as its name "stable" implies. Stable humus in the soil is like a storehouse of nutrients that are accessed only in times of low decomposing organic matter. So one could see it as a buffer for nutrients. When no or low levels of organic matter are present stable humus supplies the needed nutrients. This can only be accomplished with the help of healthy micro-flora. In addition stable humus provides a buffer for water and pH in the soil.

Charles Darwin on earthworms.