Winter crops are often talked about as a win–win for agriculture. In general, they protect the soil by replacing bare winter fallow. By recycling nutrients, they set the stage for better yields in the next crop. Overall, winter crops should make farming systems more resilient and efficient. But in places with sandy soils and warm, wet conditions—like much of the southeastern United States—nutrients move quickly. That means the benefits don’t always show up where we expect them.

“Timing really matters here,” said Julia Barra Netto-Ferreira, a recent Ph.D. graduate in the UF/IFAS Department of Soil, Water, and Ecosystem Sciences (SWES), now an assistant professor at the University of Maine. “Fast residue breakdown means that long gaps between termination and planting give mineralized nitrogen more chances to be lost.”

Her dissertation research involved a recent two-year field study examining how different winter crops influence nitrogen cycling and corn performance. The goal was to see what these systems can realistically deliver.

The study focused on sandy soils, which are common in Florida and notoriously difficult to manage for nitrogen. These soils drain quickly, have low organic matter, and allow nitrogen to cycle and escape rapidly, especially under warm and humid conditions. To explore whether winter crops could improve nitrogen availability and reduce fertilizer needs, researchers compared three winter cropping strategies—chickpea, crimson clover, and rye—to a traditional winter fallow. They planted corn after each treatment with either low or high nitrogen fertilizer inputs.

Legumes and rye

Winter crops, particularly legumes, clearly stimulated soil nitrogen cycling.

“Legumes bumped up potential N mineralization compared to rye and fallow, most notably right after termination,” Barra Netto-Ferreira said.

Chickpea and clover residues, which had relatively low carbon-to-nitrogen ratios, broke down quickly after termination. This increased the amount of nitrogen that could potentially become available to crops.

“It’s not just how much residue you have—it’s the quality,” explained Gabriel Maltais-Landry, SWES associate professor and Julia’s faculty advisor. “N‑rich legume residues accelerate N mineralization and increase N availability in the soil in ways rye and fallow don’t.”

These treatments also boosted the abundance of soil microbes involved in nitrogen fixation, nitrification, and denitrification, resulting in more biologically active soils compared to fallow plots. A graduate Southern SARE (Sustainable Agriculture Research and Education) grant that Julia wrote and executed made it possible to look at soil microbes in detail, especially the abundance of important functional genes.

The rye crop mostly produced more biomass. However, its residues had higher carbon-to-nitrogen ratios and did not significantly increase nitrogen mineralization compared to fallow. Instead, rye tended to retain nitrogen in the soil, slowing its release rather than directly supplying it to the following corn crop.

Impact on yield

Despite improvements in soil nitrogen processes, corn yield responses were inconsistent. Fertilizer nitrogen rate and year-to-year conditions impacted yields more than the choice of a winter crop. Even when legumes contributed nitrogen to corn, the amount was modest and highly variable.

“Using nitrogen isotope tracing, we found that corn took up only a small fraction of residue-derived nitrogen,” said Chris H. Wilson, an associate professor in Agronomy and Julia’s co-chair. “Much of it either stayed in the soil temporarily or was likely lost before the crop could use it.”

In the study, crimson clover showed the most promise under low fertilizer inputs. Its greater biomass and nitrogen mineralization occasionally led to improved corn performance. Chickpea strongly stimulated microbial activity. However, it sometimes showed neutral or even negative relationships with yield.

“This highlights how timing, residue management, and crop demand all matter,” Julia said.

Rye, meanwhile, appeared better suited for nitrogen retention than for supplying nitrogen directly to corn.

Building the soil

The main takeaway from this work is that winter crops can improve soil function without necessarily boosting short-term yields—especially in sandy, fast-cycling systems.

“Given the small and variable N credits, the real wins are in soil function and internal N cycling,” Maltais-Landry said.

“The study shows winter crops enhance biological activity,” Julia said. “This is a positive for row crops in the long-term and hopefully this can eventually lead to greater yields or crop nutrition.”

Funding for this research came from Southern SARE (Sustainable Agriculture Research and Education) via grants LS21-353 and GS22-262. The resulting research article is published in the journal Biology and Fertility of Soils and available on its website.

Featured image from Julia Barra Netto-Ferreira.

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