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by Simon Poeschl
When I was asked for writing some blogs about sustainability, I've thought many times how to start that column. Lots of ideas came to my mind but at least I decided it would be the best beginning with dirt. Why dirt? Our planet is covered with 70% water, so our ancestors could have called it ocean. The atmosphere is 70km thick, so they could have called it air. But they called it earth (Claude Bourguignon)! After life we'll turn back to the ground. We all even exist because of soil and so it has an essential meaning for human beings on that beautiful planet.
But what's meant exactly when we talk about soil? For answering this question I want to make a short introduction to pedology (soil science). Scientifically soil is defined as the biologically active earth crust of land surface, but that layer's thickness can be very different (Scheffer/Schachtschabel 2002). In some fertile areas you can find soil in 15m depth. At the opposite there isn't any more soil in a few fully degraded areas. All the dirt we see in our landscape came to existence a long time ago by physical and chemical weathering of parent rock material. This parent rock material consists of lots of minerals which can be fractioned in for creatures’ available nutrients. Nutrients are available for plants on soil particles' surface. That's why a bigger surface comes along with a better nutrient supply. Thereby you can imagine how much time it takes to build up soil when it was degraded ones, here an example. We contemplate a piece of granite with a surface of 0,0002 m²/g. In temperated climate conditions it takes about 10.000 years until it will be fractioned, but afterwards it has an surface of 100 m²/g. With other words: Just some plants are able to get a very small amount of nutrients out of a piece of granite, but in a hand full of dirt can be available a huge amount of nutrients and smallest soil creatures, too. Most of these micro bacteria, fungi and small fauna species like earthworms live in the uppermost soil horizon. They are the reason for life on earth because they assume the work of disaggregating dead organic matter which means bringing nutrients back to the soil and provide them for further organisms. Additionally some special species of fungi, called mycorrhiza, cooperate with about 90% of our earth' land plants in symbiosis. The mycorrhiza get sugar which is assimilated by plants and support plants by giving them additional nutrients or serving as buffer referring to toxic substances like Aluminum. But what is the connection to the greater topic sustainability?
As we know we still have an increasing human population in the world. Contemporaneously losing soil belongs to the biggest problems we are faced with in these times. Degradation and soil erosion are serious problems which are mainly results of conventional agriculture. As you read above how important soil organisms are, imagine what happens with soil when a tractor with trailer rides on fields which can weigh up to 50 tones. Every life inside the upper soil is almost gone. In winter time fields are naked and vulnerable. So if wind or strong rain comes, it will take away the light and weak soil particle which means essential nutrients fly or flow away. Because of that we lose about 2cm soil every year on average. Like humans' reaction when we are hurt soil wants to protect itself, so it starts covering the soil with fast growing plants – some call them pest plants. Pesticides are the conventional answer, which are made of fossil mineral oil. In summary we see that humans need and use a lot of energy to work against nature because we get told that this way is the only one that can feed the world. That there are exist other possibilities which base on working together with nature, I want to tell you in further blogs.
