On a third of the arable land in the world, more of the cultivation layer is lost than fertile. Experts warn that this erosion is eating away the very foundations of our existence. According to a UN University study, encroaching deserts could make fifty million people in Africa and Central Asia obliged to flee over the next decade. Raine and Thomas want to understand how desertification occurs and what you can do about it. Therefore they start to investigate the shifting sands around their school.
Worldwide, and also in Europe, many areas have changed from rich natural environments to barren sands. By studying the soil closely, you can begin to understand how this can happen. Raine and Thomas have made a soil profile of the nature reserve behind their school. What they noticed was that there are different layers in the soil profile: pale and dark sand layers alternate.
"To understand something about the soil, it is important to know the history of an area," their teacher says. During their research, Raine and Thomas discover that there were old settlements near their school. Raine: "The farmers used to cut down the forest and let their sheep graze on the arising heathland. In the evening the sheep went into the stable. On the stable ground the farmers would put down scraped up heather. The farmers mixed this heather with the sheep's faeces and then they used it to fertilise their fields. The areas where the sheep were grazing thus became poorer and poorer, meanwhile the scraping eroded the soil even more and created drifting sand. As the plants and humus layer disappeared, the soil could no longer remain moist and there were no longer any roots to hold the sand, so the wind could cause the top layer of the soil to drift. A hundred years ago, farmers started using artificial fertiliser, which caused the poor drifting sand areas to become overgrown again."
The teacher says: "In the past, heathland was part of agriculture, but nowadays we think heathland and shifting sand areas are beautiful and we call it nature. Due to the use of artificial fertilisers, dehydration (lowering of water levels) and acidification, a lot of nature is disappearing and the nature that remains is poor. Raine responds, "It’s still strange that we are now making an effort to preserve heathland and drifting sand areas, while they have been created by deforestation and (too) intensive agricultural use, while elsewhere in the world attempts are being made to prevent desertification by combating deforestation and over-intensive grazing!"
In the soil profile found by Raine and Thomas, the top layer of yellow sand is drift sand: it has drifted over the original heathland soil. On top of the subsequent grey layer used to be heathland. Because the soil here is naturally acidic and the average rainfall in the Netherlands is high, many plant nutrients dissolve in the top layer of the soil and sink deeper into the soil. Since there’s less acidification deep under the ground, the nutrients dissolve again (precipitate). You can see this by the very dark brown layer underneath the grey layer, which is formed by iron oxides (rust). Below this layer you will find drift sand again. If you scrape the heathland soil down to below the iron layer, the sand underneath will start to drift and you will get a drifting sand area instead of a heathland area