Act: Inspiration

Making And Keeping Soils Fertile: The Case of the Island Poel

July 15, 2020

“We owe our entire existence to 6 inches of topsoil and the fact that it rains.”

The fertility of the soil is one of the most vital, if not the most important factor in farming. The soil is the very basis of agriculture! And its composition, structure and condition determine how abundant the harvest will be.

Soil could be called the “skin” of the Earth. It is the hotspot of interaction between the underground of our planet and the atmosphere.

Soil is created when rocks and sediments are weathered below the ground. This happens when larger rocks are crushed into smaller ones by high pressure, freezing, volcanic eruptions, sedimentation, biodegradation, through the work of glaciers, wind or water solubilization. These processes, of course, take millions of years, until the fine-crumbed soils we know are formed. It takes roughly 10 000 years to form 150 centimetres of topsoil.

When you take a closer look at soil, you will notice that it can vary much from one another in colour and texture, and can have a different “touch”, depending on where it is found. This is due to the different factors that influence it, such as climate and relief, and its varying historical formation processes, such as formation during a glacial series or a deluge. Soil structure is of course also very much affected by the vegetation that covers it or the creatures that live in it. Even though the soil might look “dead” at first sight, millions of living beings inhabit it, from tiny bacteria to moles and worms.

The human factor

One last factor that affects the soil is – man. This might look like an unimportant factor, considering that it takes such vast periods of time to form soil. But I dare to say that humans have a major influence on the state our soils are in. Humans are the only beings that can decide what will be ‘planted’ on a patch of land – a crop, a pasture, a highway, a factory or a city. They control the way soil is tilled and manured. And precisely these decisions determine the state our soils are in.

In the case of agricultural land, this determines firstly whether soils give harvest abundantly or not. Secondly, this makes soil a carbon storage. In both cases, the magical word is humus.

Let me explain.

Why humus matters

Humus is the finely structured organic matter in soil. It is created in a process called humification. Basically, it is a decay-process. The living beings inhabiting the soil, like bacteria or mushrooms, decompose (“digest”) residues of plants, animals or other soil matter.

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Humus is beneficial in many ways.

  • Soils that are rich in humus retain moisture and nutrients better. Humus feeds microorganisms in the soil, who are, in turn, responsible for making nutrients accessible to plants.
  • Soils with an active microbial life generally have a better structure. This is because these creatures make the soil crumblyaerated and well infiltrated by rain. These soils are also more tolerant in case of droughts or lacking nutrients, since they can store large quantities of nutrients and water over a longer period of time.
  • In addition, the black colour of soil organic matter helps soils to warm up quicker in spring. Isn’t nature perfect?

Dark colour of soil is a sign that it contains a lot of humus. Photo by

Carbon storage

Another very important benefit of humus is that it stores carbon dioxide. This is especially important in terms of climate change. Greenhouse gas levels, such as CO2, are increasing at a worrying rate in our atmosphere.

Humus is largely composed of carbon (C), originating from the CO2 of the atmosphere. This means that, the more humus we have in our soilsthe less we have in the atmosphere. Each additional ton of humus can discharge the atmosphere of 1,8 tons CO2 (since CO2 is made up of 0,55 tons C and 1,25 O2). (1)

Enough reasons to maintain and enrich soils with humus! This is no easy task, since humus is at the same time created and again decomposed. This means that, even though organic matter is added to the soil (by manure for example), nearly the same quantity of organic matter will be decomposed in the meantime.

Still, it is possible to steadily enrich the soil with humus – talking of an increment of 30% in a period of some 10 years.

The other side of the story

At the same time, it is possible to withdraw humus from the soil.

Unfortunately, soil degradation is very common on agricultural land worldwide. This happens when the field loses more nutrients and organic matter than it gets back (as compost, manure etc.).

Another important way of soil degradation is erosion. Humus is mostly found in the topsoil, where most living beings reside, but this topsoil can be easily destroyed by frequent ploughing, wind and water erosion (as in this spectacular case). In events of heavy rain or wind, soil that is momentarily not covered by plants or is located at a slope, is either washed away by water or carried away with the wind, irreversibly.

Remember that it takes 10 000 years to create 150 centimetres of topsoil. In other words, 1,5 millimetres of soil are created per annuum. In contrast, 10 million hectares of farmland are being degraded each year worldwide. (i.e. lose more fertile topsoil than is being created)! (2)

Fertile soils, rich in organic matter and soil organisms, are a precious good which we must protect and treasure.

The “super soils”

The most fertile soils on Earth are the so-called black soils or chernozems. These are found in some areas in North America, Central Europe, Eastern Europe and Russia. It took several millennia and a specific climate and steppe vegetation for them to form. Their humus layer can be thick up to 1.5 metres and contain 4 – 16 % organic matter (as a comparison, most agricultural soils have a humus layer thickness of 10-20 centimetres and contain about 2 – 4 % organic matter).

For a long time, scientists thought that such “super soils” can be formed only under these specific circumstances, with no significant human influence.

The case of the island Poel

But a peculiar case has captured the interest of researchers. This is the case of the island Poel, located in the Baltic Sea in the North of Germany. On this island, as well as some other places around the Baltic Sea, thick, dark chernozems were found in a patchy distribution.

Since the climatic conditions in this area do not correspond at all to the typical conditions presumed to have influenced other chernozems worldwide, the question arose what had led to the formation of these soils. A series of investigations, delving into the precise composition of the soil organic matter of the chernozems on Poel, revealed that they had been formed in a time period between the Bronze age and the Early Middle age, mainly by the amendment of combustion residues and marine biomass (seaweeds). (3)

You can see the thick layer of dark soil on the top of this cliff on the island Poel. Photo by Naomi Bosch

Human agricultural activity has led to the formation of soils rich in humus into depths of up to 70 centimetres – a soil every farmer would dream about!

Good stewards of the land

But as if this revolutionary discovery wasn’t enough, a look into some historic documents on the island of Poel revealed that its agricultural land had received a special treatment (4), saving the soil organic matter from degradation. Farmers had been applying a wide crop rotation of 9 to 11 different crops on their farmland. Crop rotation, in contrast to monoculture, is a successive cultivation of different crops in a specified order on the same field. It is another useful tool for enhancing the organic composition of soils.

Additionally, the farmers were committed to build hedges around their plots as a protection against wind erosion.

Sadly, under economic pressures, most farmers today apply a crop rotation of only 2 to 3 different crops on their farmland, or, even worse, plant monocultures of just one crop year after year. In combination with erosion, this practice exhausts the soil, leading to degradation and ultimately, after many years, infertility of the soil. In light of these facts, it must have taken genius and a lot of foresight to cultivate the farmland on Poel with such care and diversity.

What’s happening with our soils?

According to the FAO, chernozems in the Ukraine have contained a humus layer of three metre thickness in the beginning of the 20th century. Today, these layers have shrunk to 1.5 metres of thickness.

In only 100 years, humans have managed to degrade something that has taken thousands of years to form!

In their article Human activity formed deep, dark topsoils around the Baltic Sea (3), the scientists proposed to classify the black soils in the Baltic Region as “Anthrosols” – soils formed by anthropogenic activities. This should make us thoughtful on the role we, as humans, have in forming our environment.

Our influence can stretch from devastatingly harmful to beautifully healing and regenerating. We can act either caring, using our intellect in foresight, or helplessly ignorant, degrading the basis of our existence. We have the power to use our intellect for the benefit of creation, humans and the environment.

And this is indeed a daunting, but beautiful task! A task we are all in as inhabitants of the Earth, whether as consumers or producers of food.

Thank you so much for reading! Around Christmas, I will be publishing a special three-part series where I write about my personal journey to understanding the challenges that agriculture faces today. I will share what I believe the underlying causes are, and how these could be solved looking at some ancient Jewish literature. You can sign up to my newsletter and receive these articles straight into your inbox!

(1) A. Idel: Die Kuh ist kein Klimakiller! (Metropolis, 2010)
(2) D. Pimentel, Professor of Ecology at Cornell University. Journal of the Environment, Development and Sustainability (Vol. 8, 2006)
(3) Acksel et al.: Human activity formed deep, dark topsoils around the Baltic Sea (Geoderma Regional Vol. 10, 2017)
(4) J. Saegebarth, H. Baudis, Dr. Schröder-Lembke: Insel Poel – Beiträge über Landschaft und Geschichte (Koch & Raum Wismar, 2007)

Naomi Bosch

grew up in Croatia, having a garden & nature close by. In 2017, I moved to the North of Germany to study agriculture. I have worked on various farms since. To me, it is always a pleasure to work in agriculture and discover the way farmers live. Through this blog, I want to invite you on a journey to discover plentiful lands all around us.

Tags: rebuilding resilient food and farming systems, soil health