As well as being desirable from an environmental perspective, healthy soils also permit higher yields. Yet many agricultural practices accelerate soil degradation, while climate change and biodiversity loss exacerbate problems.
This has prompted countries all over the world to introduce policies designed to protect the quality of their arable land—clearly with some degree of success, as the new study shows. “We compared satellite images from 2001 through to 2019,” explains Guyo Dureti. “This enabled us to measure how the biomass of agricultural crops has changed year on year in the areas cultivating them.”
Analyzing 250,000 areas spread across the globe
The economist and agricultural scientist is studying for his doctorate at the University of Bonn in the Land Economics Group led by Professor David Wuepper, a member of the Cluster of Excellence “PhenoRob” and the Transdisciplinary Research Area (TRA) “Sustainable Futures.” Analyzing the satellite imagery was merely the first step in the study, because an increase in agricultural biomass does not necessarily indicate an improvement in soil condition. After all, the differences could instead have been caused by natural climate factors (e.g. changes in precipitation and temperature levels) and agricultural practices such as applying more fertilizer and investing in mechanization and irrigation.
The researchers—Dureti, Hadi, and Wuepper—therefore worked to eliminate these influences, again using high-resolution satellite measurements of the local microclimate, fertilizer use and irrigation to give them reliable indications of soil quality. They performed this calculation for more than 83 million pixels spread across the globe, each representing one square kilometer, to track the change in soil condition for all the world’s farming regions.
Gauging the impact of national policies
“We were mainly interested in the influence wielded by regulations, agri-environmental payments, and similar policies at national level,” Dureti says. “Among other things, therefore, we used a kind of ‘natural experiment’ approach.” This involved the researchers studying pairs of neighboring countries where one had introduced a new safeguard and the other had not. They compared the change in the soil before and after the regulation came into effect, focusing on border regions in order to eliminate the influence of any local idiosyncrasies as far as possible. “If the soil immediately north of the border develops differently to that right to the south, this is likely to be because of the new law,” Dureti points out.
This enabled the researchers to demonstrate that government measures to combat degradation are actually working. They found that one particularly effective tool is financial incentives that reward farmers for taking care of their cropland, e.g. by optimizing their use of fertilizers, switching to more eco-friendly weedkillers and pesticides or planting hedges to prevent soil erosion. Regulations that directly address how land is to be managed (e.g. through crop rotation) or that aim to make certain landscape features such as wildflower strips mandatory also have a major impact.
Strong government institutions key to success
Whether or not regulations imposed by the state will achieve the desired effect, however, depends very much on the underlying political and institutional conditions. Thus, a greater impact is to be found in countries with strong government institutions. By contrast, where there are few or no opportunities to monitor compliance with statutory regulations and enforce them when necessary, they will rarely prove successful. Factors such as corruption also have an adverse effect. There is another link too, and one that should come as no surprise: The more money countries spend on protecting their soil, the more success they will have in maintaining its quality.
“Overall, however, our study sends out a positive message,” Dureti concludes. “Government regulations can significantly improve land quality and thus do much for environmental protection and food security.”
Nature Food