Humans responsible for decreasing soil quality

Published on
December 23, 2020

Never before, soils changed as quickly as over the past 5 thousand years. During his doctoral research, Marijn van der Meij discovered that people and their agriculture are mainly responsible for this change.

The quality of the soil has declined considerably since humans started using land to grow crops. An healthy soil consists of different layers. Each layer in a soil profile contains a unique composition of material and nutrients. This produces healthy, fertile soil. Van der Meij discovered that more and more of these layers disappeared as a result of human behavior. This threatens food security, biodiversity and carbon storage.

Erosion by plowing

About half of the usable land on earth is used as agricultural land. Agriculture has an enormous impact on the soil, Van der Meij discovered. Machines such as plows are partly to blame, especially when they are used on a slope. “When a plow turns the soil, fertile soil material descends,” explains Van der Meij. “The soil loses more and more of its soil layers. They pile up at the bottom of the hill.”

In the past, this would not have been a big problem because root systems stabilise the ground. But with less trees and increasingly intensive agriculture, land became more sensitive to so-called plow erosion.

Computer simulations

The PhD student discovered that people change the soil so intensively and rapidly, during a field study in Germany. He investigated which soil layers were present in the agricultural land in the study area and how old these layers are. Using computer simulations he calculate the composition of the soil thousands of years ago. “I took various natural factors and scenarios into account, such as drought or high rainfall,” says Van der Meij. "But with every calculation, simulations showed the effects of intensive farming for the past five hundred years."

Photo credits: Marijn van der Meij
Photo credits: Marijn van der Meij

Using this technique, Van der Meij simulated what the soil looked like more than 14 thousand years ago and how it gradually changed until the year 2020. For a long time, soil layers and quality changed slowly. Until five hundred years ago, when people started to use land for intensive agricultural production. From that moment on the soil changed rapidly and the variation in soil layers decreased.

With these computer simulations, scientists can not only determine what the soil looked like in the past. “We can also calculate how the soil will develop in the coming tens to thousands of years,” says Van der Meij. "You can take all kinds of scenarios into account, such as different degrees of climate change." Van der Meij will continue to work on this in the coming years.

New Age

This is not the first time that man's influence on nature has become apparent. Climate change, deforestation, water pollution, but also urbanization and infrastructure. Humans are adapting their environment at such a rapid rate that scientists have even named the era in which that happens, the Anthropocene.

Marijn van der Meij obtained her PhD cum laude from Jakob Wallinga, professor of Soil Geography and Landscape.