Re-evaluation of manganese solubility as affected by soil sample preparation in the laboratory

Abstract

Laboratory experiments were conducted to re-evaluate the effects of drying and the time between drying and Mn analysis on soil Mn solubility using maize seedlings as test plant. Samples of five soil types were collected in the field, transferred to laboratory and submitted for the following treatments: dried in the shade at 25ºC and dried at 65ºC followed by Mn determination immediately and after 30 and 60 days. Ninety days later soil samples were rewetted at field capacity and maize seedlings were grown for 7 days. Evaluations included plant Mn content and soil Mn extracted with NH4OAc 1 mol L-1 pH 7. The lowest soil and plant Mn contents were found in soil samples dried in the shade at 25ºC. Drying soil sample at 65ºC and increasing the time between drying and Mn analysis increased Mn solubility and Mn uptake by maize. Oxisols showed higher soil and plant Mn contents than other soil types. The results indicated the extreme difficulty in interpreting soil Mn results due to the great effect of soil processes in the laboratory on Mn solubility. Routine soil analysis is not recommended to evaluate plant available Mn.