Project results will be shared through printed media (e.g., University of Delaware Weekly Crop Update, University of Delaware fact sheets, Maryland Agronomy Blog, etc.). Project personnel will also present results of the work at Mid-Atlantic Crop School (reaches up to 300 regional Certified Crop Advisers) and the Delaware Ag Week field crop Agronomy session (reaches up to 500 regional grain producers).

Updated May 1, 2022:
See attached file.

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Micronutrient deficiencies, particularly manganese (Mn), are often overlooked, but can significantly reduce soybean yields. Sandy soils with low buffering, like those on the Mid-Atlantic Coastal Plain capacity are especially susceptible to higher pH, which limits plant availability of Mn. The objective of this research was to evaluate the tissue and yield response to foliar Mn application when Mn deficiency is predicted by a pre-plant routine soil test.
In cooperation with local farmers, we established replicated in-field strip trials in 2019 and 2020 and small-plots at the University of Delaware Warrington Irrigation Farm in 2020 to evaluate foliar application of Mn to soybean at two rates (0 and 1.5 lb/ac Mn) on crop yield and tissue concentrations. Initial soil test reports collected from participating farmers included soil test Mn interpretations that suggested soils were within the low to sufficient ranges for Mehlich 3 Mn. However, Mn deficiency was unlikely based on the calculated Mn availability index (MnAI), which was above 35 for all sites.

Yield data was collected at harvest using a calibrated yield monitor. Plant tissue samples were collected at pod fill from the University of Delaware site only in 2020. We reported no significant yield or tissue Mn response to foliar Mn application. as the soil pH and Mn concentrations were conducive to soil Mn availability. As such, we do not recommend that farmers apply foliar Mn unless soil MnAI is below 25 or if Mn deficiency was observed and documented previously by a tissue test.

However, soybean is known to be a Mn sensitive crop and Mn deficiencies have been documented in poorly buffered sandy Delaware soils. Soil testing remains the best line of defense against soybean Mn deficiency. Growers and consultants should use soil test Mn concentrations and soil pH values to calculate the MnAI based on the most recent soil test rather than relying on interpretation charts alone. For fields with soil MnAI between 25 and 35, we recommend scouting in-season for Mn deficiency symptoms, and confirming suspected deficiencies with a tissue test prior to application of foliar Mn.

Additional research is needed on soils with suspected Mn deficiency (MnAI <25) to determine the economic value of foliar Mn applications to soybean.