Thank you Henrik for organizing this. Hello and welcome, dear students. My name is Jeff Von Trapp. I am professor at DTU. I'm an ecologist and a gardener. And I have learned about the value of soil and how to make good soils and I would like to think about soils and land management. And to start with, I would like to say that culture, the word coltura, that comes from agriculture, the way we treat our land. The short presentation is about soil management and soil degradation. I will talk about the origin of soil, the value of soil and the threats to our soils like depletion of soil, salinisation, pollution and erosion. I'll give you a short outlook into the future. The origin of our soils. Some 10, 15,000 years ago, Denmark was covered with ice. And when the ice retreated, there was nothing but bare rocks and stones and bad weather. And this bad weather gave weathering. And from the weathering we got the first fine dust. On these rocks and stones, lichens and algae were growing, and these decayed and gave the first organic matter in which first small higher plants were living. And as we see on the slide from these first higher plants developed roots and litter, and by the help of bacteria and mushrooms, the first cover of soil developed. This progressed on and we got large forests, and within 12,000 years about 10, 15, 20 meters of topsoil formed. Well, the story continued and the forests were cut off and agricultural land was there, which is now used to grow our fruits and crops. Plants need so little to grow. They need carbon dioxide. They need sunlight. They need water and nutrients, and that's it. The latter two, water and nutrients, they get from soil. If you look at the distribution of cropland on the world and there's a map now to see, we see that Europe has good cropland. Most of Europe is used for agriculture. We have croplands in Ukraine, in Russia, in India, in China. Also in North and South America. In particular in the East. We have no cropland in the Baltic and Nordic region, because it's too cold. We have no cropland in the deserts, and we also have little cropland in Africa. About 30% of the Earth's wetland area is already used for crops, for agriculture. It's 70% pasture and 30% for crops, its 5 billion hectare. And we have 5% irrigated ecosystems rise in China, for example, but these produce 40% of the harvests approximately. Around the world the best soils are used for crops. And the peak area of land was reached in the 1990s. That means since then we have not got more new soils. There are larger unused fertile areas, mostly in the tropical rainforest zones. In South America, Brazil, in Africa, and in Sumatra, Indonesia, but do you really want to cut down the rainforests and get the last soils for agriculture? Still, despite that we have reached the maximum soil area, we still have an increase of yields. And this is because progress in agriculture. The fertilizer, the new seeds, the pesticides, and also the gene technology still provide us with progress. But we come to a plateau. The increase in yields is slowing down, and we probably cannot produce much more food than now. But we are still increasing consumption. Not only increasing numbers of humans, we also have an increasing need for animals and an increasing need for energy use. This means there is not too much food on this world. That was the introduction, now we come to the threats for the soils and we have first of all the depletion of fertility by overuse. I have a very good slide to see here, which shows the value of good soil. It's made in Denmark, on. And in the front of the picture, we see what grows on a stony soil. Almost nothing, a few bare weeds. And that is behind a layer of 87 centimeter compost. And we get two meter height plants. Green. So this shows how important soil organic matter is for the growth of plants. It provides water and nutrients. Soil depletion means that the soil fertility decreases with time. There's more and more nutrients taken from the soil, but also the soil organic matter decreases. It's accumulated on unused lands by the remainders of the plants, the roots, the straw. And if these yields are extracted from the soils, then the soil organic matter is depleted. And I'm very concerned that now with this new biogas boom, all the last residues from the fields are taken and used for biogas, and that the depletion will be even faster. Compost, compost is the gold of the farmer. The second big threat is soil erosion. And soil erosion often occurs when the soil is bare. That means when forests wither, they're cut down, or when the land is bare, for example, mice production, then the erosion by wind and water can take away the fertile topsoil leave spec, stony bare soils. This is seen all over the Mediterranean area where forests covered the mountains, and already in Roman times for forests were cut down, and what remains is very bad soil and and shrubs. The main reason for this soil depletion is overgrazing, it's overuse, it's deforestation, and it's other agricultural activities. So mainly, bad land management and overuse. And you see on the slide, the percentages. Another threat is salinisation. As I said before 5% of the land is irrigated now and the numbers are very much increasing because by irrigation you can yield higher harvest in hot areas, hot deserts like Israel, Spain, China. The problem are two. If there's too much water used for irrigation, and then there is water logging, and the salt water or the salty water cannot leach out salts from the soil and they accumulate. But also if too little water is used, then the plants take up all water and they can't excrete the salt, and that is, the salt also gets salty. And salt is very toxic to our cash crops. So the salts are more or less useless after some time. The slide shows a natural salt island in the Okavango Delta where the plants took up the water, left the salt. And this increases more and more. Fortunately, there's hope. We have identified more than 2,000 plant species which are very resistant to high salt levels are salt tolerant, these are not cash crops but they could be an alternative on salty soils. Another threat we face in particular in urban areas is soil pollution and I can tell you that all soils in old cities are polluted. We see a map here of Copenhagen. And most of the inner city is suspect of soil contamination. This is heavy metals, it's arsenic, it's tar, its oil. But also on agricultural land we have pollutant problems. For example, from cadmium and phosphate fertilizer. Which accumulates over time into topsoil. Yeah, so this is not so much a problem for the harvest yields. But it means that our harvest product is toxic and cannot be marketed and is worthless. Finally, a threat, soil coverage and compaction. As you see here, we have buildings we have ways. And of course, where is a street nothing can grow and even after removal of the street, the good soil doesn't come back. The topsoil is taken away, the soil is compacted and there is no more agriculture possible. This is, in all urban areas, a problem and the cities are growing and very often, the cities are in the most fertile areas. The river deltas, [COUGH] in the river valleys, so what you see it the land is lost for human nutrition. Good. Finally, an outlook. We see a map of the children per man and woman and most population growth nowadays is in Africa. As we saw before, Africa has very little agriculture land that has the potential to use. But there's also vivid overgrowth of mankind. So there, we will face in the future most problems like soil depletion, erosion, land overuse, and urbanization. Thank you very much for your attention and thank you very much for the chance to speak here to you. Bye bye.
