Growing up, you likely heard at least one of these sayings from the so-called “Mom’s Handbook”: “Everything in moderation,”
“Too much of a good thing is never good” and/or “variety is the spice of life.”
The same can be applied to soybeans. Continuous crop soybeans in the same field, and you may pay a yield penalty, according to long-term research.
Granted, sometimes Mother Nature throws a wrench in even the best-laid plans, like in 2019.
Saturated soils in the Mid-South prompted many growers to switch from planting corn in late winter to waiting for the ground to dry and planting shorter-season soybeans.
A handful of research projects in the Midwest found a 3% to 19% yield advantage for corn following soybeans and up to a 10% yield advantage for soybeans after corn compared to continuous beans.
But the work was conducted in states like Wisconsin, Iowa, Ohio and Illinois, where soil types, soil temperatures and soil saturation are different from the Mid-South and may affect winter soil nitrogen loss.
This lack of local data prompted researchers from Mississippi State University, University of Arkansas, Louisiana State University, Texas A&M University and the University of Missouri to conduct a multi-year, multi-state project examining soybean rotations.
Titled the “Effects of the Introduction of Feed Grains into Mid-South Soybean Production Systems,” it ran from 2014-2019, with some locations continuing the project for additional years.
Altogether, the research involved six locations and 12 crop rotations, with seven being irrigated and five under dryland conditions. Among the treatments were continuous corn, continuous soybeans, a soy-corn rotation and various combinations.
The corn-soy rotation produced increased yields in a number of the plots. In the others, there was no significant difference among the different treatments. The researchers are still examining how the different rotations affected soil nutrient composition.
Planting continuous soybeans also may promote build-up of plant parasitic nematodes. Once you’ve sent soil samples to the lab and received nematode species identification, rotation with a non-host plant — such as corn or grain sorghum — may be part of an integrated management program, according to several state Extension soybean specialists.
Soybean taproot decline, an up-and-coming soilborne pest across much of the South and Mid-South, also appears more prevalent in fields with at least two years of soybeans than in fields with only a single year of beans. Based on preliminary work, researchers suspect the fungal pathogen may overwinter on plant matter, only to infect the following year’s soybean crop.
See, Mom was even right about soybean rotations.