Soybeans can remove significant amounts of nutrients per bushel of grain harvested. As a result, they may sometimes respond well to starter fertilizers, depending on several factors, says Dorivar Ruiz Diaz, Kansas State Research and Extension (K-State) nutrient management specialist.
“The most important factor is the fertility level of the soil. Soybeans will respond to direct fertilizer application on low-testing soils, particularly with regard to phosphorus,” he said.
K-State soil test recommendation guidelines for soybeans include phosphorus (P), potassium (K), sulfur, zinc and boron, Ruiz Diaz explains.
The most consistent response to starter fertilizer with soybeans would be on soils very deficient in one of those nutrients, or in very high-yield-potential situations where soils have low or medium fertility levels, he says.
If fertilizer is recommended by soil test results, then fertilizer should either be applied directly to the soybeans or applied indirectly by increasing fertilizer rates to another crop in the rotation by the amount needed for the soybeans, he says. The method of application is important.
“Banding fertilizer to the side and below the seed at planting is an efficient application method for soybeans. This method is especially useful in reduced-till or no-till soybeans because P and K have only limited mobility into the soil from surface broadcast applications,” the K-State agronomist says.
However, with narrow-row soybeans, it may not be possible to install fertilizer units for deep banding, he adds.
“In that situation, producers can surface-apply the fertilizer. Fertilizer should not be placed in direct seed contact with soybeans because the seed is very sensitive to salt injury,” Ruiz Diaz says.
Soybeans seldom respond to nitrogen (N) in the starter fertilizer, although that’s not to say it can’t happen, he said. “Some past research in irrigated, high-yield environments at K-State’s Irrigation Experiment Field in Scandia suggests a potential benefit of small amounts of N in starter fertilizer, as long as it is not applied directly to the seed,” he adds.
In addition to directly benefitting soybeans in some cases, starter fertilizer in soybeans also can be a good way to complement nutrients that may have been removed by high-yielding crops in the rotation, such as corn, Ruiz Diaz says.