Thursday, July 23, 2015
Lessons of Ancient Soils
Fig.1. Rice fields in Vietnam (Credit: Mayur Kakade via United Nations Flickr)
Since the advent of agriculture around 12,000 years ago, soil degradation has plagued farming societies. On average, soil is only about a meter thick, but its nutrients, water, and even structure are vital for healthy plant growth. As humans modified the land for urban or agricultural use, soil became less nutrient-rich and prone to erosion.
An international team led by researchers at the University of Vermont calculated that European settlement and farming in the 1700s increased rates of soil erosion by a hundredfold. This agricultural intensification, which occurred at a great cost to our soil, became the norm around the world to increase crop yield and feed a growing population.
A recent study published in the journal Catena connected agriculturally-derived degradation to ancient human migration. Study co-author Sjoerd Kluiving and colleagues at the VU University of Amsterdam examined soil core samples from archaeological sites around the Netherlands. Grain size, chemical concentrations, and soil organic carbon confirmed that continuous settlement and farming since the Early Bronze Age used up local nutrients.
Kluiving et al. also found that human settlements from 1000 BCE until 500 CE shifted to areas with better soil conditions. As soil degrades, its physical, biological, and chemical characteristics change. Soil becomes less porous, loses phosphorous and nitrogen, and experiences a shift in the community of microorganisms underground. The researchers documented these changes and compared soil cores to reference soil samples which came from archaeological excavations that had been dated. The application of soil cores, modern soil maps of Europe, and older excavations all served in this interdisciplinary study to track human migration through agriculture.
This pattern seen in soil cores has repeated itself around the world and throughout history. Whether we study sediments from the 1700s or 1000 BCE, humans change their landscape irreparably. Nearly 40 percent of Earth’s terrestrial surface is now used for agricultural purposes. With a projected population of 9 billion people by 2050, experts expect a 70 percent increase in demand for food, feed, and fiber.
Unlike in the ancient Dutch settlements, we can no longer move to more habitable lands. Fortunately, modern conservation techniques - such as no-till plowing, crop rotation, and cover crops - have significantly reduced erosion rates in some areas. Further studies of microbial communities indicate that these agricultural practices directly affect bacterial functions in the soil. We can learn our lesson from ancient soil degradation and work to sustainability support a larger populations in the coming years.
Amundson, R., Berhe, A. A., Hopmans, J. W., Olson, C., Sztein, A. E., & Sparks, D. L. (2015, May 8). Soil and human security in the 21st century. Science, 348 (6235). doi: 10.1126/science.1261071.
Brown, J. E. (2015, January 07). Hello People, Goodbye Soil. University of Vermont Communications. Retrieved from http://www.uvm.edu/~uvmpr/?Page=news&storyID=19904
Iacurci, J. (2015, May 07). Soil Loss Threatens Food Security. Nature World News. Retrieved from http://www.natureworldnews.com/articles/14590/20150507/soil-loss-threatens-food-security.htm
Kluiving, S. J., et al. (2015). Mass migration through soil exhaustion: Transformation of habitation patterns in the southern Netherlands (1000 BC - 500 AD). Catena. doi: 10.1016/j.catena.2014.12/015.