A nearly decade-long study on crop rotation and nitrogen loss has revealed that less tilling and a more varied array of crops can help improve nitrogen retention in soil without affecting yields.
The research was led by Lowell Gentry of the University of Illinois at Urbana-Champaign and spanned 2015 through 2023, as a report shared by Phys.org explained.
Scientists compared a typical two-year corn and soybean rotation with a more intensive three-year rotation that included corn, cereal rye, soybean, and winter wheat. The latter improved the nitrogen capacity of the soil. Nitrogen is a valuable crop nutrient.
"Subterranean drainage pipes called tiles transport nitrogen, in the form of nitrate, from fields to streams, impairing downstream surface waters," the scientists wrote.
Artificial drainage is needed for crop production, but the nitrate can be lost from the rooting zone with tile water, Gentry explained.
Other studies have shown that about 50% of nitrogen fertilizer used on crops is lost through runoff, polluting nearby waterways in the process.
Nitrates can also move along major rivers such as the Mississippi and end up in the Gulf of Mexico, contributing to a vast oxygen-starved "dead zone," as the researchers put it.
"Our study was designed to see if a more diverse crop rotation could reduce tile nitrate loss and still be competitive with the conventional system of corn and soybean," Gentry added.
The intensive three-year crop rotation involved planting corn, followed by soybeans and then winter wheat. After a summer harvest of wheat, soybeans were planted again, with a winter cover crop of cereal rye to help protect the soil. This last crop was terminated through herbicide before the next planting round so it could decompose and deliver more nutrients to the soil surface.
Another key difference between the standard two-crop method and the three-year rotation is that the former is fully tilled, while the latter strip-tills a third of the soil each rotation. That means it takes nine years for the varied crop field to be fully tilled.
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Definitely 😭 "It's very expensive to make fertilizer, and so I think it's much more strategic to try and conserve the nitrogen, meaning keep it in the field, don't let it leave in the first place," Gentry said. "And that's what the cereal rye and the winter wheat can do. They suck up enough nitrogen during the fall, winter and spring to lower the soil nitrate level. That reduces the tile nitrate level."
Less tilling also seemed to let the biodiversity of the soil flourish, resulting in a bounty of earthworms, which have been shown to keep plants and crops healthy.
This crop rotation plan can also work in tandem with scientific methods used to improve crops at the genetic level, further bolstering their potential yields and improving food security.
"This study is a proof-of-concept that a more diverse rotation can achieve this sustainable intensification, reducing nitrate losses while also improving soil quality," Gentry said. "Hopefully, recreating conditions that promote the natural processes of soil generation will improve soil quality and soil health, reversing the decadeslong trend of declining organic matter across our agricultural soils."
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