Reaction of MnEDTA Applied Alone or with Ammonium Polyphosphate Fertilizer to Soils1
- J. J. Mortvedt2
Manganese ethylenediamine tetraacetate (MnEDTA) applied alone to some low-Mn, high-Fe soils generally is not an effective Mn source for plants; apparent substitution of other soil cations for Mn in MnEDTA decreases plant availability of applied Mn. A laboratory study was conducted to estimate cation substitution for Mn in MnEDTA by determining changes with time in H2O-soluble cations in treated soil. Four moist soils (pH 5.4 to 7.7) were treated with MnEDTA at rates of 0, 25, and 100 ppm Mn; soils were aerobically incubated up to 148 days. In addition, MnEDTA was applied to these soils with 10-15-0 (10-34-0 oxide basis) fluid polyphosphate fertilizer at rates of 1,500 ppm P and 100 ppm Mn. The application rate simulated that in soil around a fertilizer band of 10-15-0 containing 1% Mn at a rate of 50 kg of P/ha (100 lb of P2O5/acre).
Water-soluble Mn increased with MnEDTA rate in all soils just after application but decreased with time to the level of untreated soils. In soils treated with MnEDTA alone, H2O-soluble Fe increased with time in acid soils, and H2O-soluble Ca increased in limed or calcareous soils, suggesting substitution of these cations for Mn in the EDTA molecule. Levels of H2O-soluble Mg, Zn, and Cu in all soils were not affected by application of MnEDTA.
Application of MnEDTA with 10-15-0 reduced the apparent rate of cation substitution for Mn in MnEDTA by precipitation of competing cations in soil. Thus, Mn in MnEDTA should remain available to plants for a longer time with band application in fluid polyphosphate fertilizers than with mixed application alone or with other fertilizers to soil.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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