A study from South Dakota State University (SDSU) indicates tillage reduction leads to increased soil organic carbon levels and better-yielding soybeans and corn. SDSU distinguished professor David Clay has watched this for more than twenty years.
“This organic matter helps hold water, it reduces erosion and that water that that soil holds is provided to the plants that are growing during the growing season,” said Clay. “And it can help fill the gap during rainfalls that oftentimes don’t align with what the crop needs during a growing season.”
In the 1800s, South Dakota prairies were being homesteaded by settlers arriving from the east, according to a news release from SDSU that outlined the history and scientific evolution of Great Plains conservation. Early on, farmers used the moldboard plow to turn over and aerate the soil, helping to control weeds and prepare the soil for planting. The practice was successful in growing crops, but it also led to the Dust Bowl. That ecological catastrophe was partly caused by the destruction of native prairie grasses and excessive tillage of fertile topsoil. Those tillage practices also led to low levels of soil organic carbon, which it was later learned plays a key role in soil health. Carbon is a component of organic matter and contributes to nutrient retention, soil structure and water storage within soil.
Over the course of two decades, analysis of more than 12 million soil samples from South Dakota, Iowa, Minnesota and Nebraska showed soil carbon increasing, in some cases, more than 400 pounds per acre per year resulting from tillage reductions.
“That carbon got to a certain point, and our microbial communities got to a certain point, and what they were doing is they were getting that material that the nitrogen and the nutrients contained in the organic matter and they were decomposing that more rapidly,” Clay told the South Dakota Soybean Network. “And it was being mineralized and made available to the growing plant. Along with reductions in our tillage, it allowed us to reduce our nitrogen rates approximately 50 pounds per acre.”
As one might expect, an added benefit to tillage reduction or elimination is good old-fashioned conservation of soil resources.
“What we’re seeing is large reductions in erosion,” said Clay. “Reductions are somewhere between 20 and 30 percent. So, it’s making a big difference in what’s coming from our fields and moving into our streams and rivers.”
For maximum benefit, Clay recommends adhering to the soil health principle of covering the soil and minimizing tillage intensity.
“So, that residue covers that soil during a period of time from harvest until planting in the following year,” he said. “And it really protects that soil and reduces that runoff and erosion.”
How much carbon is enough and is there such a thing as too much carbon?