By Erhard Hennig
Editor’s note: This is an excerpt from Acres U.S.A. original book, Secrets of Fertile Soils, written by Erhard Hennig. Copyright 2015, softcover, 198 pages. $24.00 regularly priced. SALE PRICE: $19.20.
Humus forms as a result of the complicated interplay of inorganic conversions and the life processes of the microbes and tiny creatures living in the soil. Earthworms play a particularly important role in this process. Humus formation is carried out in two steps. First, the organic substance and the soil minerals disintegrate. Next, totally new combinations of these breakdown products develop, which leads to the initial stages of humus. Humus formation is a biological process. Only 4–12 inches (10–30 centimeters) of humus-containing soil are available in the upper earth crust. This thin earth layer is all that exists to provide nutrition to all human life. The destiny of mankind depends on these 12 inches!
Cultivated soils with 2 percent humus content are today considered high-quality farm land. What makes up the remaining 98 percent? Depending on the soil type, soil organisms constitute about 8 percent, the remains of plants and animals about 5 percent, and air and water around 15 percent.
The remaining 70 percent of soil mass is thus of purely mineral origin. The mineral part of the soil results from decomposition and the erosion of rock. The dissolution of these components is carried out by the lithobionts, which can be seen as the mediators between stone and life. It was, once again, Francé who coined the term “lithobiont,” which means “those who live on stone.” The lithobionts are the group of microbes that begin the formation of humus. They produce a life-giving substance from the nonliving mineral. On the basis of this process, living matter, earth, plants, animals, and human beings can begin, step by step, to build.
Only soils with an optimal structural state of tilth have a humus content of 8–10 percent. Untouched soils in primeval forests can, at best, reach 20 percent. A tropical jungle can’t use up all its organic waste, so humus can be stored. All forests accumulate humus, but real humus stores only emerge over the course of millenniums. Once upon a time accumulations of humus known as chernozem (Russian for black earth) could be found in the Ukraine.
Almost all plant communities (except for leguminous plants and untouched forests) use up more humus than they can produce. Strictly speaking, each harvest and each growth of cultivated plants is accompanied by a loss of humus, a problem which is aggravated from year to year. The lost humus cannot be replaced by any kind of mineral fertilizer. Both deciduous woods and mixed forests can provide their own humus because they are able to make use of their own discarded leaves.
Even in nature, without human influence, humus is only produced in deciduous forests and on undisturbed land.
Humus is favorably disposed towards the vegetable rather than the animal metabolism. This is why manure, with its high proportion of animal excrement, cannot support natural humus formation. Manure has to be turned into humus before it can be used for fertilization.
Why is this? The microbes living in the soil are more favorably disposed towards the decomposition of pure cellulose than towards the disintegration of animal excrement, which leaves the intestines in an anaerobic state. This fact was unfortunately not recognized by earlier generations.
Rather than being subjected to aerobic decomposition, manure was commonly simply buried in the field. When introduced to the soil in this way, the rotting anaerobic matter remains an alien element for quite a long time. The rot substances are disintegrated by specific rot microbes, whereas the microbes inherent to the soil, living under aerobic conditions, are driven out. The question of whether anaerobic or aerobic microbes predominate, and therefore whether rot or decomposition occurs is crucial for susceptibility or health of the plants grown in a soil. The following example reveals how little humus is produced when manure is used: if a dose of 400 quintals of stable manure is applied to each hectare of soil (on light soils), then after half a year, half of the amount of the manure can be found, after one year only a fifth, and after two years practically nothing of the manure is left. The organic matter in the soil is quickly consumed and assimilated then mineralized without the production of humus.
Typical manure cultivation has been practiced in Germany for the last two hundred years, which if manure cultivation were effective would mean that this country has soils very rich in humus, but that’s not the case at all. Manure is only the remains of the substances that served the animal as nutrition. All the highly nutritive proteins, carbohydrates, fats, and so on that were produced by the plant have been taken away from the soil, and the excrement is poor in nutrients.
In spite of these shortcomings, the custom of manure spreading is still widely practiced. Here is an example; several years ago a renowned child specialist wanted to find out whether the quality of vegetables grown for babies and young children was influenced by fertilization.
Erhard Hennig was an agronomist who devoted himself to agriculture from an early age. He worked extensively as a farmer, agricultural consultant, journalist, author, and lecturer and worked and taught at Humboldt University in Berlin. Hennig died in 1998.