Insight Sustainabilty 3: SOIL_Column by Simon

MapMakersWorld Author: Simon Poeschel

At first please excuse the long break after my last blog. Amongst others I spent four weeks on my bike cycling through northern Italy. The matter of fact that you can find in almost every small village a small café, restaurant and food store, even if there is a supermarket, fascinated me. But to this story I'll come back in one of the next blogs more detailed.

Maybe my last blog ended up in some questions for you about how to practice agriculture and concurrently protect the soil from degradation. Before responding to this topic I want to do an excursion about the necessity of humus in soil. So what's humus? Humus is dead organic matter (DOM) which is already transformed to fertile soil by earthworms and other smallest organisms. The typical black color and structure like crumbs make the estimation comparatively easy how much humus you have in the upper soil. Generally you can say the stronger the black color the higher is the soil's humus content. But why do we need this fancy dirt in our soil? Humus has the ability to save a lot of water, is full of nutrients and has a low density which result in better conditions for plant growth. Most of the DOM is accumulated aboveground, but of course it originates belowground, too, when plants and their roots die. Like I told before humus is transformed DOM mainly by earthworms. Logically small organic matter like leafs can be used earlier by them than bigger ones like wood. Certainly there are differences in assimilating organic litter concerning time. For example conifers' litter contents a lot of acid which earthworms don't tolerate. That's why it's fractionized by special fungi which takes much longer than earthworms need for eating broad-trees' leafs. But life conditions of earthworms depend on so much more than only on the kind of litter. Most of their species need a soil pH between 4 and 7. Similar to micro bacterias they prefer a high carbon/nitrogen proportion (1/6 would be perfect). Because they also need oxygen for living, which they absorb out of water through their skin, the surrounding soil should be humid but not wet. They like warm conditions, but if it's too hot they are cooked. Of course there are a lot of different earthworm species. For example there are specialists who mainly dig vertical canals and don't tolerate any daylight (so you can just see them at night – generally these are bigger worms). Other ones turn DOM in humus very fast and can be seen also at daytime by turning the upper soil layer a little bit where they live. The vertical canals can be used by plants for growing their roots and the soil can absorb a lot of water inside them. These canals are so stable that researcher even found a few closed to Göttingen, Germany, which exist since our last ice age – 18.000 years ago.

So why do I tell you earthworms' life conditions? I want you getting more conscious in walking through our nature. When you walk through a forest full of broad trees next time, take a look on the ground. How much litter do you find down there? Do you find only a few leaves and under them mineral soil already starts than mainly you have two options: First it's a place which gets affected by wind or water erosion (maybe on hillside). Second it's a place with high bioturbation which is a result of high earthworm activity. With other words you can say that they eat the organic matter, upgrade it in their stomach, and bring it downstairs in soil where the humus is protected from erosion and can be used by plants. If you find fermented leaves (from the last year), the activity will be still fine. When the activity decreases, there's a tiny layer (between a few millimeters and 4-5 centimeters) as the next criterion which is comparable to coffee ground. The last grade with lowest soil activity interrelates to a very low pH value (lower than 3-3.5) and usually they originate in forests with conifers. It is recognizable easily, because it's possible to break our “coffee-ground-layer” (no more powdery).

So I hope this blog was neither too much nor too less detailed and you're already glad about the following one which will explain the necessity about closing nutrient circles and how to do this easily in our daily life.