11 January 2024

Cover crops are a barrier against agriculture-based pollution


According to a U.S. study, the application of cover crops on a share of cultivated land reduces the maximum concentration of ammonia and phosphorus by more than 30 percent. Whose accumulation is favored by floods

by Matteo Cavallito


Some agricultural strategies, such as cover crops, can significantly mitigate water pollution. A phenomenon linked to climate change, which is known to make flood events increasingly frequent thereby promoting the dispersion of agricultural and livestock residues through them. This is suggested by a research.

The study, by the University of Illinois Urbana-Champaign, which involved researchers from other universities, analyzed rainfall data collected over more than a decade in the state of Wisconsin where a large dairy sector exists. Here, the authors note, livestock manure and crop fertilizers are the leading causes of agricultural pollution.

After heavy rains, spikes in nutrient concentrations are observed

Studying water quality in nearly 50 Wisconsin watersheds from 2008 to 2020, says a statement by the University of Illinois, the authors correlated ammonia and phosphorus concentration data from the Water Quality Portal with the location of farms and cropland. In this way, they determined nutrient levels after rainfall of half an inch, one inch and two inches (equal to about 1.3, 2.5 and 5 centimeters) per hour.

The researchers, the statement continues, found spikes in nutrient concentrations immediately after extreme rainfall events. This effect increased as rainfall intensified.

Up to five days after a rainfall event with an intensity measured in one inch (about 25 millimeters) per hour, the level of ammonia in the soil had increased by 49 percent, that of phosphorus had increased by 24 percent. When there was at least one day of rainfall intensity greater than 10 mm, the monthly ammonia concentration figure was 28% higher, the phosphorus figure was 15% higher.

The importance of mitigation practices

“We observe a significant interaction between rainfall, agricultural production, and runoff. It is not just a short-term spike in nutrient levels; at the end of the season, we still see persistent increases in phosphorus and ammonia attributed to those extreme precipitation events months earlier,” said Marin Elisabeth Skidmore, professor in the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois. At the same time, however, the researchers also noted how some good agricultural practices can effectively help curb the phenomenon.

Cover crops, in particular, appear to have a strong impact by once again proving capable of mitigating the negative effects of climate change.

“We find that a hydrologic unit with 10% of cropped area planted in winter cover crops will experience a 32% lower ammonia spike and a 36% lower phosphorus spike, compared to one with no winter cover crops,” the study says. “This beneficial effect of cover crops even persists to end-of-season phosphorus concentrations.”

Cover crops are an essential resource

The research brings the role of cover crops back into the spotlight. In 2022, a study by the University of Córdoba, Spain, showed how their use drastically reduces organic carbon loss by strengthening the structure and cohesion of soil particles. The investigation focused on olive groves in Andalusia, which, the researchers noted, have high erosion rates due to a combination of factors that includes heavy rainfall and conventional tillage.

In the soils examined, the scientists recalled, cover crops had been responsible for an average of 36.7 percent reduction in runoff and 85.5 percent reduction in erosion. The practice also had reduced sediment-associated carbon loss by 76.4 percent. Providing far greater protection from the effects of rainfall than was found in soils subject to traditional tillage.