Factors such as erosion, dehydration and compaction of the soil are jeopardizing food supplies for broad swathes of the world's population according to a recent study by the University of Bonn, the University of Minnesota, the University of Basel and Hamburg University of Technology. If human-made soil degradation were to be reversed by 10 percent, the Earth's arable land could feed an extra 70 million or so people in purely mathematical terms. The findings have now been published in the journal "Nature Food."
Not only are slash-and-burn agriculture, overfertilization, and monoculture on a huge scale threatening ecosystem biodiversity, but many current farming practices are also doing long-term damage to soil quality. This problem is being exacerbated by human-made crises such as climate change, with storms and heavy rainfall causing fertile topsoil to be blown or washed away. On top of this, groundwater levels are falling, not least because precipitation often comes in such heavy concentrations that it simply runs off instead of seeping into the ground.
Degraded soil is known to be less fertile. However, the severity of this effect and its impact on crop yields have been something of a bone of contention up to now. "Now, for the first time, we've attempted to quantify the consequences of degradation for all the arable land around the world," explains Dr. Hadi Hadi, a postdoctoral researcher in the Land Economics Group at the University of Bonn, who carried out many of the analyses for the recently published study.
How much could soils yield that were unaffected?
The researchers involved in the study started by asking themselves how high yields could be in practice without any degradation. To this end, they first divided all the arable land on the planet into squares 10 kilometers long and wide. "We then looked for squares with similar prevailing conditions, i.e. comparable precipitation levels and temperatures, and compared the yields in these areas," Hadi says.
Adjusting their figures to account for differences in the use of fertilizer, irrigation and other cultivation factors enabled the researchers to identify areas with particularly high yields. Many of these were also those that had sustained hardly any soil damage up to that point. "Thus, these areas give us a benchmark for what's possible in soils that haven't been degraded or influenced in any way," explains Professor David Wuepper, head of the Land Economics Group.
Machine learning uses gaps in yield to calculate degradation rate
For each 10 × 10 km parcel of land, therefore, the working groups involved were able to calculate a specific "yield gap," which they then correlated with five different parameters connected with soil degradation: erosion, dehydration, compaction caused by the widespread use of heavy agricultural machinery, the loss of carbon dioxide in the soil, and minimal vegetation cover. "Rather than gathering this data ourselves, we drew on detailed studies by various working groups," Wuepper points out.
With the aid of complex AI-powered evaluation methods, the researchers were able to use the yield gap that they had identified to calculate the degree of soil degradation in each parcel. "Taking an average of all the parcels gives us an approximate rule of thumb," Hadi says: "A 10 percent increase in the degradation rate cuts the yield by an average of 2 percent. Conversely, if we could reduce degradation by 10 percent all over the world, crop yields would grow by such an extent that we'd be able to feed over 70 million more people."
Soil deterioration can be stopped
"Overall, the findings show how important soil quality is to the supply of agricultural produce," says Wuepper, who is also a member of the PhenoRob Cluster of Excellence and the Sustainable Futures Transdisciplinary Research Area. Grounds for hope in this regard have been furnished by another recent study by his working group, in which researchers were able to demonstrate that soil degradation can be slowed or even reversed by means of regulations and agri-environmental payments at national level (press release: https://www.uni-bonn.de/en/news/141-2026 ). In other words, it is not a foregone conclusion that the quality of our soils will keep on getting worse at the hands of intensive farming.
Institutions involved and funding secured:
The University of Bonn collaborated on the study with the University of Minnesota in the US, the University of Basel in Switzerland and the University of Hamburg in Germany. The research work was funded by the European Research Council (ERC), the German Research Foundation (DFG) and the Swiss State Secretariat for Education, Research and Innovation (SERI).
