According to a new study from South Dakota State University’s Department of Agronomy, Horticulture and Plant Science, corn and soybean yields have increased dramatically since 2000 in some states. In South Dakota, Iowa, Minnesota and Nebraska, corn yields are increasing at over two bushels per acre per year, and soybean yields are increasing at over half a bushel per acre per year. While better crop varieties are credited with some of the increase, the SDSU researchers say reductions in tillage intensity is also a major contributor.
According to Deepak Joshi, a graduate of SDSU and now an assistant professor at Kansas State University, and David Clay, Distinguished Professor of soil science at SDSU, the study reveals soil organic matter levels are increasing at a rate of over 650 pounds per acre per year. Higher levels of soil organic matter greatly contribute to improved soil health. The researchers attribute improved soil health to increased conservation practices like reduced or no-tillage.
Intense tillage was a successful method for growing crops in the U.S. prairies when settlers first started to arrive in the 1800s. The process helps control weeds and aerates the soil in preparation for seeding. But intense tillage practices also came with downsides as it led to historically low levels of soil organic carbon. Many believe that the Dust Bowl, the greatest ecological disaster in modern history, was partly caused by the overtilling of fertile topsoil.
Armed with better information, U.S. farmers from the 1980s onward began gradually adopting conservation tillage and then no-tillage systems. Surveys conducted between 1985 and 2010 found that in the Great Plains, farmers rapidly adopted no-tillage systems as it increased soil water storage and improved their crop’s profitability. By 2012, no-tillage was used on approximately 33% of U.S. farms. A survey conducted between 2018 and 2021 found 77% of eastern South Dakota farmers used some form of reduced tillage system.
Clay and his team felt a comprehensive study was needed to better understand the relationship between soil organic carbon levels, tillage reductions and yields. Analyzing data over a over a 21-year period (2000-2021), including over 650,000 surface soil samples from South Dakota, the researchers determined that on a yearly basis, 428 pounds of carbon per acre were being stored annually in South Dakota’s fields.
Expanding the research to other states and utilizing over 12 million soil samples South Dakota, Minnesota, Iowa, and Nebraska, the team says farmers in these states have stored approximately 1.24 billion metric tons of carbon in the six inches of surface soil over the 21-year period. Within the four-state region that tillage intensity decreased, corn and soybean yields increased +63 and +33%, respectively.
“In addition to the large amount of carbon that was stored, improvements in soil health most likely contributed to the reduction of sheet and rill erosion, which decreased by 22.8%, 14.3%, 27.5% and 31.5% between 1987 to 2017 in Nebraska, Iowa, Minnesota and South Dakota, respectively,” according to Clay.
The increasing levels of soil organic carbon can be attributed to greater residue, like corn stover, corn root and corn exudates, that remains in the field following harvest. This material, known as nonharvested carbon, is decomposed by organisms in the soil and converted into humus—dark, organic material that forms when plant matter decays. Humus provides many benefits to the soil and is measured by researchers as soil organic matter.
At the same time, Clay and his team emphasize that higher yields are a result of several factors, including improved genetics and soil health. As Clay notes, it is clear that these factors work in tandem to produce a feedback loop that is increasing soil organic matter and, in turn, boosting yields. Each year, the loop continues forward, simultaneously increasing soil organic matter levels and yields.
Clay says that the increase in soil organic carbon levels in South Dakota fields may mean farmers do not need to use as much nitrogen for their corn crops as they traditionally would. That’s because improved soil health leads to enhanced nitrogen use efficiency. In 2024, a team of researchers reported that in South Dakota, nitrogen recommendations can be reduced by approximately 25% without reducing corn yields.
The SDSU team also believe the increase in soil organic carbon levels is linked to better resilience against extreme weather events. Because high levels of soil organic carbon help improve water storage capacity, the resiliency of South Dakota’s soils has increased, allowing them to better handle droughts. This is evidenced by previous research, which compared the economic impact of the 1974 and 2012 droughts in South Dakota.
The full study, titled “Tillage intensity reductions when combined with yield increases may slow soil carbon saturation in the central United States,” is available HERE.
