By Dan Davidson
DTN Contributing Agronomist
An application of starter fertilizer may give soybeans a head start in the spring when planting earlier than normal. As with corn, when soils are cool in the spring, dry or too moist, soybean seedlings have few roots to intercept nutrients and soil organic matter isn't yet mineralizing nutrients. A band of available nutrients at the first rootlet interface can overcome any immediate deficiencies.
A Pennsylvania grower recently asked if starter fertilizer is worth the investment in soybeans. He said starter is important in his no-till corn program, but wanted to know if it works as well in soybeans.
"I routinely apply pop-up fertilizer of 4 gallons per acre of 9-18-9 white acid (in-furrow) and 20 gallons per acre of 30-0-0-2S in a 2-by-2 band for planting corn. I have had good success establishing no-till corn for the last 20 years," he wrote. "Recently I planted my first-ever soybean crop using no at-planting fertilizer as I was concerned about fertilizer sensitivity for soybeans. I intend to no-till plant future soybean crops early, before my corn crop. Most growers in western Pennsylvania use no at-plant fertilizer, but a respected friend from Ohio thinks it might help early in the season when it is typically cold and damp spring and especially (in) no-till. So can you apply a starter fertilizer on soybeans and if so what are the rules?"
With so many growers planting soybeans earlier in April at the same time as early corn, using a starter makes sense, especially if you no-till. Make sure to account for the N, P and K in your starter as part of your overall nutrient budget.
Whether starter pays on soybeans depends on the season, soil conditions and planting date. I consider it a risk-management tool that helps ensure every plant gets off to a good and fast start across every acre. That's a prerequisite to high yield.
University soil fertility specialists historically advised against starters as soybeans are more sensitive to salt than corn. With corn you can apply 5 gallons per acre in-furrow as long as your salt index doesn't exceed 10 to 12 pounds of nutrients (N and K) per acre. In a 2-by-2 band you are unlimited and volumes of 20 to 30 gpa are common. I've used popup with soybeans but limit the volume to 2 to 2.5 gpa with 3 to 5 pounds of nutrients (N and P) per acre. I like to dilute that to 4 to 5 gpa with water to reduce the risk of salt damage.
The risk of injury is lower if you band in 2-by-2, use a low-salt starter, have soils with higher cation exchange capacity and soil is moist or it rains a day after planting. So for corn I consider 20 pounds the top rate for a 1- by 1-inch band and 45 to 50 pounds top for the 2- by 2-inch band. In soybeans I would cut that back to 10 and 25 pounds, respectively.
Soybeans need phosphate, potash and sulfur, just like corn, so adding some through a starter makes sense. When it comes to making a nitrogen recommendation on soybeans, currently one of the few sound recommendations is to apply some nitrogen preplant or as a starter. The plant's early growth can benefit, it can help with residue decomposition, and if the spring turns wet into June, that nitrate will keep the plant growing when the otherwise wet conditions will prevent nitrogen fixation.
(GH/SK)
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