Crop Rotation and 2nd Year Soybean Yields

By Matt Hutcheson, CCA, Soybean Lead/Field Agronomist, Seed Consultants, Inc. and The SCN Coalition

As we begin to make plans for the 2024 growing season, growers will determine what crops to plant and plan crop rotation across their acres. When considering crop rotations and yields, many focus on continuous corn and the yield penalties associated with that practice. However, there is one possibly overlooked benefit of crop rotation: avoiding a soybean yield penalty.

In this article, the University of Kentucky’s John Grove discusses soybean yields for first year and second year soybeans from 2009 to 2016. Grove’s research data shows an average yield penalty of 2.3 bu/ac across that 7 year period, with some years being showing yield losses greater than 10 bu/ac. In another article from No-Till Farmer, Greg Roth shows data that predicts a 4 to 6 bu/ac yield penalty for second year soybeans.

Yield loses from continuous soybeans (and other continuous crops) are usually associated with increased disease presence as well as pests. Diseases that can over-winter on crop residue can be more severe for second year soybeans, especially in no-till production systems. Soybean cyst nematode presence can also increase with continuous soybean production. Additionally, weeds that are difficult to control in soybeans (marestail, etc.) can spread and rob yield as well.

No-Till Farmer also published an article about managing risk in second year soybeans. Practices such as crop rotation, varietal selection, seeding rates, row widths, and tillage practices can be used to mitigate yield losses in soybeans.

A recently completed multiyear study that compared corn-soybean rotations to corn-on-corn and soybean-on-soybean rotations conducted by researchers at the University of Wisconsin (UW) provides more reason for concern. The study found a traditional corn and soybean rotation produced greater yields than continuous planting of either crop.

SCN soil testing was incorporated into the UW research, and SCN population densities were greater in consecutive years of soybeans versus rotating with a non-host crop like corn. “The negative effect of SCN on soybean yields is well documented, and protection against SCN is critical to maintain top-end soybean yield potential,” says Shawn Conley, one of the authors of the research and a UW professor of agronomy.

“These results were not surprising,” Conley adds, “and certainly reinforce The SCN Coalition’s recommendation to rotate SCN-infested fields with a non-host crop.”

As growers look forward to the 2024 season, yield losses from continuous soybeans should be considered when determining acreage for crops to be produced.

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