Manganese deficiency in soybeans is an annual management issue on high pH, high organic matter soils in Michigan. Soil characteristics render soil Mn unavailable for plant uptake, necessitating in-season foliar fertilizer applications to meet plant Mn requirements. In 2009, research studies were established at two central Michigan muck soil locations. Fertilizers were applied either as tank-mixes with glyphosate when possible or separated by at least three days before or seven days after glyphosate. Three Mn fertilizers were evaluated: MnSO4, a sugar alcohol Mannitol, and MnSO4 chelated with EDTA. All fertilizers alleviated Mn deficiency in the field, but MnSO4 application was most effective at increasing tissue Mn concentrations. Manganese fertilizers influenced soybean leaf Mn levels similarly when tank-mixed with glyphosate or applied separately. Manganese deficiencies reduced yield at three of the six sites years. At one responsive site, all fertilizer treatments increased yield above the control. At the two other responsive sites, MnSO4 and Mannitol applied separately from glyphosate resulted in the greatest yield. A second project to evaluate additional Mn fertilizers was initiated in 2010 at the same two muck soil sites. Fertilizers were applied at a low and high rate as suggested on product labels. At both sites in 2010 and 2011, two fertilizer applications were required to treat Mn deficiency symptoms. MnSO4 tended to increase tissue Mn concentrations compared to other products. Manni-plex, Citraplex, and Max-In applied at the high rate generally resulted in higher leaf Mn level compared to other products. Products with EDTA chelates often did not increase tissue Mn levels above that of the untreated control. Applications of MnSO4 at both high and low rates and Citraplex, Manni-plex and Max-In at high rates consistently resulted in higher yields. The use of unchelated or low molecular weight fertilizer products increase foliar fertilizer uptake and result in higher yields than products with higher molecular weight EDTA formulations.As part of a broad six-state project to address agronomic limitations of soybean yield and quality, trials were initiated in Arkansas, Iowa, Kentucky, Louisiana, Michigan, and Minnesota to examine the impact of P and K fertilizer strategies on corn and soybean grain yield. Fertilizer rates were determined by local state recommendations for a two year corn-soybean rotation and applied at 1x and 2x rates for each crop annually in the spring before crop establishment or biannually as one application both crops prior to corn in the first year. Corn grain yield was increased by fertilizer application at five of twelve sites with initial soil test P and K values in the medium range or higher. At sites with either P or K soil test values below the medium soil test range, increases in corn grain yield with fertilizer application were noted at five of eighteen sites. Yield responses were variable, with increasing fertilizer rates associated with decreasing corn yield at some locations. Soybean grain yield was increased at three site years, all at locations with soil test P in the medium or lower range. No clear trend was observed at these three sites indicating a difference in annual and biannual fertilizer applications. These results uphold current university P and K fertilizer recommendations.
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