By Mike Staton, Michigan State University Extension
There is growing interest in using starter fertilizer (in-furrow and 2x2) in soybean production. Historically, starter fertilizers have not produced consistent yield increases in soybeans. There are several possible reasons for the few and inconsistent soybean yield responses:
•Phosphorus and potassium soil test levels were above the critical levels.
•Planting conditions (soil temperature and moisture) were ideal.
•The starter fertilizers did not provide adequate amounts of the proper nutrients.
This article will focus on the last factor and provide information on which nutrients are most likely to produce a positive yield response when included in a starter fertilizer for soybeans. Again, this doesn't ensure that a positive yield response will occur. It only improves the probability of a positive yield response.
Most universities recommend placing soybean starter fertilizer in a band 2 inches to the side and 2 inches below the seed (2x2). This method significantly reduces the risk of salt injury to the seed. Because of the reduced risk, the 2x2 placement method enables producers to apply higher levels of essential crop nutrients than is possible with in-furrow applications. All starter fertilizer application rates provided in this article are for the 2x2 application method.
Starter fertilizer can contain up to 100 pounds of P2O5 and up to 60 pounds of K2O per acre. If nitrogen is included in the starter, up to 20 pounds of actual nitrogen per acre can be included as long as the K2O plus nitrogen does not exceed 70 pounds per acre. Sulfur may be beneficial on coarse-textured soils having low organic matter levels and can be safely applied up to 15 pounds per acre.
Both phosphorus and potassium should be included in a soybean starter fertilizer. Phosphorus promotes early root growth and potassium has been shown to increase soybean root nodulation and biological nitrogen fixation. Small quantities of nitrogen – 10 to 20 pounds of actual N per acre – may promote early growth, but have rarely increased soybean yields in university research trials. This level of nitrogen should not reduce root nodulation or biological nitrogen fixation.
Including 2 pounds of actual manganese per acre, or the recommended amount based on a soil test, in the starter may improve plant growth and yields when soybeans are produced on lake-bed or glacial outwash soils having pH levels above 6.5. Liquid manganese fertilizers (EDTA chelates) are relatively expensive, so this practice may be feasible only when using dry starter fertilizer (manganese sulfate). Foliar applications of manganese fertilizers are effective for correcting deficiency symptoms and are an excellent alternative to applying manganese in the starter fertilizer.
For more information about applying manganese foliar fertilizer, please see the Michigan State University Extension article "Identifying and correcting manganese deficiency symptoms in soybean."