By Carol Brown
University of Missouri agronomist Tim Reinbott spends much of his day immersed in agricultural history. An assistant director at the Central Missouri Research, Extension and Education Center (REEC) near Columbia, Reinbott also oversees Sanborn Field, which is a part of the center. Established in 1888, Sanborn Field is the oldest, continuous experimental field west of the Mississippi River and the third oldest in the world, according to its website.
Through managing the plots at this historic site, Reinbott is seeing the benefits of longer crop rotations. This spurred him to conduct research on how longer crop rotations could be used today for improved crop productivity as well as soil health.
“Since the establishment of Sanborn Field, researchers were using six-year crop rotations as the farm was centered around real horsepower rather than tractor horsepower. The crop rotations included oats and timothy,” explains Reinbott. “Because we don’t need these crops now to feed working horses, they shortened the rotations at Sanborn in 1990. Now I wonder if that was a mistake.”
Reinbott is managing a research project, supported in 2022 by the Missouri Soybean Merchandising Council, that compares one-year up to five-year crop rotations for productivity, soil health and water quality. He has included plots with cover crop mixes, no cover crop, tilled and no-tilled as part of the many equations. Reinbott’s study, broken down by year, is illustrated in Table 1.
He began the rotations in 2016, long before any external funding came along. Now all the plots have completed full cycles including the five-year rotations and those are well into a second five-year cycle. Reinbott and his team are sampling the soil to study the biological and chemical properties, which in turn affect soil physical properties. They measure soil water content in addition to collecting crop yield data. The cover crop mix in the study includes cereal rye, hairy vetch, Austrian winter pea and crimson clover.
“In the plots with the cover crops, we have seen yield boosts. We had a 10-bushel increase in soybeans in our three-year rotation with cover crops,” says Reinbott. “That shows cover crops can provide benefits even in the short-term — and that’s just the yield benefit. Cover crops are also improving soil health, which perpetuates higher yields.”
Cover crops are known to protect soil from wind and water erosion with the aboveground biomass keeping soil in place. Below ground, they can also improve soil nutrient levels, aeration and water filtration. Reinbott says it takes at least four years of cover crop usage to begin to see chemical, biological and structural changes in the soil.
So far, he’s found that a four-year rotation of corn, soybean, wheat with red clover overseeded into it, and a year of red clover has the greatest impact on soil structure.
“When I’m out in the field, it’s really interesting to actually see the physical change in the soil,” he comments. “I can see an echo effect, which lasts for two or three years. I can see it in the crop growth, yields and in the soil health.”
In the other part of this study, University of Missouri Extension Ag Economist Joe Horner will break down the economics of all the combinations. He is currently conducting the analysis to make economic sense of the many combinations being studied.
“Dr. Horner recently sent me his initial report and it looks like the four- and five-year rotations were the most profitable,” comments Reinbott. “All other treatments decreased returns, and the continuous crops were the least profitable. A full economic analysis will be shared once it is finalized.”
Farmers may want to conduct soil tests beyond nutrient content to establish a baseline. They should see if the soil in their fields has good structure (aggregate stability) and water availability. Based on these results, farmers could re-assess their crop rotations to build back soil health for the long term.
“I appreciate the Missouri Soybean Merchandising Council for providing funding for this study,” Reinbott says. “We want farmers to be productive and profitable and if they can build their soil structure, it will only help. They’ve got to consider five years, 10 years, and 25+ years from now — the short, medium and long-term when it comes to soil health.”
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