Effect of Fertilizer Reaction and Placement on Availability of Manganese

Manganese deficiencies are a serious problem in crop production on some high pH soils of the lake bed regions of Michigan and Ohio. It has been observed that some fertilizers banded near the seed increase Mn availability. Several factors have been suggested to be responsible for this increased availability. A series of laboratory incubation, greenhouse, and field studies were conducted to evaluate fertilizer reaction and Mn sources on availability of Mn to sugarbeets (Beta vulgaris L.), soybeans (Glycine max L.) and navy beans (Phaseolus vulgaris L.). The incubation study showed that fertilizer sources which produce an acidic reaction initially increase the level of DTPA (diethylenetriaminepenta-acetic acid) and 0.1 N H₃PO₄ extractable Mn in the soil contiguous to the fertilizer band. After seven weeks of incubation, H₃PO₄ extractable Mn levels were not significantly different for the various fertilizer treatments. The level of Mn extracted with DTPA after seven weeks for the fertilizer sources was: DAP-Urea-KCl > control = MAP-Urea-KCl > NH₄NO₃-MCP-KCl = (NH₄)₂SO₄-MCP-KCl, where DAP = diammonium phosphate, MAP = monoammonium phosphate and MCP = monocalcium phosphate. The greenhouse study was conducted on a Tappan loam (Typic Haplaquepts) and consisted of a 2⁴ factorial set of treatments with N sources of urea and (NH₄)₂SO₄; N and P (MCP) placements of mixed and banded; and Mn levels of banded Mn and no Mn. Banded MCP proved to be as effective as banded Mn in increasing Mn availability (extractable and plant uptake). Banded Mn along with banded MCP proved to be much superior to either factor alone. Nitrogen source and placement had small and variable affects on Mn availability and were largely masked by the Mn and P placement treatments. Field studies were conducted on seven soil types to test the effect of fertilizer and Mn sources and showed the following order of tissue Mn: MnSO₄ = MnO (100 mesh) > oxysulfate (partially acidulated MnO) = Mn-EDTA = control. Tissue samples taken within five weeks of planting had higher Mn concentration for a NH₄NO₃-MCP-KCl (acidic) fertilizer than for the urea-DAP-KCl (basic) fertilizer. However, when oxidation of the NH₄-N in the basic fertilizer was more complete, the difference diminished. The results suggest that when Mn deficiencies occur early in the growing season, use of an acidic fertilizer in combination with MnSO₄ or finely divided MnO would be helpful in elimination of the problem.