Varying crop rotations and keeping the soil constantly covered with vegetation helps protect crops against droughts and floods, in addition to increasing productivity. This technique was tested in Rio Grande do Sul state, Brazil, by researchers from the Center for Carbon Research in Tropical Agriculture (CCARBON) at the University of São Paulo (USP).
The study compared traditional crops with areas that used “cover crops” – plants grown not for sale, but to protect and nourish the soil between harvests. While the traditional model suffered major crop yield declines due to extreme weather events, farmers who adopted crop diversification and the use of cover crops managed to achieve yields above the state average (reaching as high as 76% above), with much greater stability from year to year.
On the other hand, farms that followed the traditional model – such as the continuous cultivation of one type of grain after another (for example, wheat followed by soybeans) or the use of a single plant species to cover the soil – performed much more poorly. In these areas, the harvest was very close to the state’s overall average (only 8% higher) and suffered from sharp fluctuations in yield from one year to the next (ranging from 33% to 39% higher or lower), demonstrating that the simple system is far more vulnerable to climate variations and surprises.
The research was conducted over three growing seasons – between 2022 and 2025 – marked by extreme droughts and floods. The results were detailed in an article published on October 22 in the journal Agriculture, Ecosystems & Environment. They were also presented by Professor Mauricio Roberto Cherubin of the Luiz de Queiroz College of Agriculture of the University of São Paulo (ESALQ-USP) in a lecture given during FAPESP Week Netherlands.
“The study shows that to keep the soil healthy and functional, it’s essential to ensure the presence of living plants and vegetation cover throughout the year,” Cherubin explained to Agência FAPESP. “When we introduce a diverse mixture of cover crops, it’s like offering a varied and continuous menu to the soil. That keeps the soil organisms active year-round, optimizing the cycling of nutrients, the biological fixation of nitrogen, and the availability of phosphorus for the main crop,” he added.
According to the researcher, the choice of Rio Grande do Sul as an experimental site is justified by its strategic position in Brazilian agriculture and its extreme climate vulnerability. The state accounts for 8.4% of national grain production. Soybean crops in Rio Grande do Sul cover 6.8 million hectares, representing 14.4% of the total area planted with soybeans in Brazil and equivalent to 3.4% of the global market. However, the state has suffered from recurring extreme weather events: a series of severe droughts between 2019 and 2023, historic floods during the 2023/2024 growing season (which caused estimated losses of BRL 45 billion in unharvested soybean crops alone), and the return of intense droughts during the 2024/2025 growing season.
How the research was conducted
To measure the interactions between soil, management practices, productivity, and weather fluctuations in Rio Grande do Sul crops under real-world production conditions, the researchers analyzed data from 13 experiments conducted by farmers on commercial farms throughout the state.
In the most complex systems analyzed, farmers combined commercial crops (soybeans, corn, wheat, and canola) with a rich variety of cover and service crops: grasses (black oats, white oats, Ukrainian oats, rye, triticale, and millet), legumes (vetch), fast-decomposing dicots (buckwheat), and brassicas (forage turnip).
Over three consecutive growing seasons, the researchers used climate data from NASA (the U.S. space agency) satellites to compare rainfall levels in the fields with the average over the past 30 years. The period analyzed was marked by extremes: the 2022/2023 and 2024/2025 growing seasons faced severe droughts, with rainfall up to 54% below normal, ranking among the driest years ever recorded in the region. The 2023/2024 harvest, on the other hand, experienced the opposite, receiving 40% more rainfall than average. Since all the farms evaluated experienced these same severe weather conditions at the same time, the scientists were able to isolate climate from the equation. This made it possible to confirm that the differences in harvest yields were, in fact, due to the planting techniques adopted in each area.
At the 13 participating farms – located in municipalities such as São Luiz Gonzaga, Rolador, Bozano, Panambi, Boa Vista das Missões, Sarandi, Santa Cecília do Sul, Não-Me-Toque, Lagoa dos Três Cantos, Quinze de Novembro, Jacuizinho, Júlio de Castilhos, and São Gabriel – 78 soil samples were collected at a depth of 0 to 10 centimeters.
To assess soil health, the scientists analyzed 12 characteristics of the samples, divided into three main categories: chemical, physical, and biological. In the chemical analysis, they evaluated factors such as acidity and the soil’s ability to hold and release nutrients to plants. In the physical analysis, they measured how compacted or porous the soil was and its efficiency in retaining water. In the biological assessment, the team analyzed the activity of enzymes that act as a “thermometer” for life in the soil, revealing whether the soil is active and able to recycle vital elements such as carbon and sulfur.
Using a statistical technique, these indicators were synthesized into four soil health functions: biochemical regulation, physical support, water storage, and carbon storage. Based on an advanced statistical method capable of mapping direct and indirect cause-and-effect relationships, these functions were linked to the degree of plant diversity and clay content.
The analyses showed that diversifying crops significantly increased the soil’s capacity to store water, regardless of the amount of clay present in the soil. As Cherubin, deputy coordinator of CCARBON – a Research, Innovation, and Dissemination Center (RIDC) funded by FAPESP – explains, the research demonstrates that retaining more water does not depend solely on the soil’s natural physical properties (whether it is sandier or clayier, for example), but rather on the “biological structuring” generated by planting practices, such as root activity and the activity of microorganisms.
According to the researcher, one explanation for this is that the deep roots of plants used by farmers as cover crops are able to break through compacted layers and open up biological channels in the soil. Biopores – natural tunnels left by decomposing roots – act as conduits for air and water and as a veritable network within the soil, he explained.
“When the main crop, such as soybeans or corn, is planted, its roots find open paths to grow in depth without expending excessive energy, reaching moisture stored in the deeper layers during dry periods,” Cherubin explained.
Vulnerability to climate disasters
The study also showed that even sustainable practices are impacted by major disasters. During the 2024 floods in Rio Grande do Sul, nearly half (44%) of the farmers who had adopted crop diversification had to change their plans. With the soil waterlogged and the harvest delayed, they had to abandon cover crops and opted to plant commercial wheat in an attempt to quickly recoup their losses.
For Cherubin, these findings are essential to ensuring the future of so-called “rain-fed agriculture” – which relies solely on rainwater – especially in a scenario of increasingly frequent droughts and storms. He explains that healthy soil with a wide variety of roots acts as a natural “shock absorber” for crops against the weather. In practice, this eliminates instability in farmers’ lives, preventing that roller-coaster cycle of a bountiful harvest one year and severe losses the next.
The recently published study is the result of Viviana Meneghini’s master’s thesis, which was supported by a FAPESP scholarship and supervised by Cherubin.