There is concern among soybean producers that manganese (Mn) and sulfur (S) deficiencies are causing yield reductions. As such, there is a tendency among soybean producers to apply supplemental nutrient sources on most fields even without experimental evidence to support this practice. Onfarm research conducted in Perry, Mich., in the past 2 years showed that supplemental Mn and S applied at planting as a starter fertilizer was not effective in increasing soybean yield. In 2014, the farmer was interested in testing the effectiveness of Mn and S as a foliar application.

The research trial consisted of three treatments:

1. T1- Check treatment with no foliar applied nutrients
2. T2 - Foliar manganese AXILO (13% chelated Mn at the rate 1 pound per acre applied in 6 gallons per acre)
3. T3 - Foliar manganese AXILO (13% chelated Mn at the rate 1 pound per acre) plus eNhance (8.7% sulfur at the rate 1 quart per acre applied in 6 gallons per acre).

The trial was planted May 28, 2014. The plots were 12 rows wide at 30-inch row spacing. The treatments were randomized and replicated four times. Great Lakes 25-69 Group 2.5 variety was used. The planting population was 135,000 seeds per acre and the previous crop was corn. Seed was treated with inoculant prior to planting. The nutrients were foliar-applied July 17 at the first bloom. Uppermost, fully developed, trifoliate leafs two weeks following foliar application were sampled for nutrient analysis. Soybeans were harvested Oct. 22.

Effects of foliar fertilizers on leaf nutrient concentration and soybean yield – Perry, MI 2014.

*Soybean yield and leaf nutrient levels were not significantly different (p<0.05). Yield adjusted to 13 percent moisture.

The soybean yield differences between the three treatments were not significantly different (see table). Manganese and sulfur levels in the foliar tissue also were not significantly different. For soybeans, the Mn sufficiency range is 21-200 ppm and S sufficiency range is 0.20-0.40%.

The soil was a sandy loam with a 6.1 pH, Cation Exchange Capacity (CEC) of 5.7 meq/100g and soil organic matter of 1.5%. A point of noticeable interest was there were no visible micronutrient deficiency symptoms in the untreated or treated plots during the growing season. The nutrient levels in all treatments were within the established Mn and S sufficiency ranges. So any increases in Mn and S uptake, even if achieved through supplemental sources, may not have contributed to soybean yield. Additional information on nutrient sufficiency ranges is found in “Secondary and micronutrients for vegetables and field crops,” Michigan State University Extension Bulletin E-486.

The results confirm that economic yield responses to micronutrients are not consistent on coarse-textured soils with low CEC. In particular, soybeans may respond to Mn only on certain fields, most likely the high pH soils that develop interveinal chlorosis as a symptom of Mn deficiency.

Michigan farmers continue to show interest in applying micronutrients. So there is merit for continuing on-farm research towards identifying site-specific factors that would contribute to more predictable micronutrient responses.

This study was funded by the Michigan Soybean Promotion Committee. The author wishes to thank Will Willson, soybean producer from Perry, Michigan; Brian Martindale, Agro-Culture Liquid Fertilizer dealer from St. Johns, Michigan; and Mike Staton, senior MSU Extension educator, for their support and collaboration in this study.