Determination of plant-available manganese from soils by acid ammonium acetate-EDTA extraction

Authors

• Oili Mohammadi Kemira Oy, Espoo Research Centre, Luoteisrinne 2, SF-02270 Espoo, Finland
• Markku Yli-Halla Kemira Oy, Espoo Research Centre, Luoteisrinne 2, SF-02270 Espoo, Finland
• Väinö Mäntylahti Viljavuuspalvelu Oy - Soil Analysis Service Ltd, Vellikellontie 4, SF-00410 Helsinki, Finland

DOI: https://doi.org/10.23986/afsci.72396

Abstract

Manganese was extracted with a solution containing 0.5 M NH4-acetate, 0.5 M acetic acid and 0.02 M Na2 -EDTA at pH 4.65 (AAAc-EDTA) from 86 soil samples collected from plough layers in Finland. The results were compared to the quantities of exchangeable, reducible (three methods) and total Mn of the soil samples as well as to Mn uptake in a pot experiment in which four yields of ryegrass were grown. MnAAAc-EDTA ranged from 1.8 to 158.8 mg/kg, mean 32.2 mg/kg. MnAAAc-EDTA correlated more closely with reducible Mn (r = 0.82*** -0.87***) than with total Mn (r = 0.50***) or exchangeable Mn (r = 0.45***), suggesting a relationship between reducible Mn and MnAAAc-EDTA. In order to take into account the effect of pH on plant-availability of MnAAAc-EDTA, the MnAAAc-EDTA indices were multiplied by two different pH correction coefficients. The pH correction resulted in a closer correlation between MnAAAc-EDTA and exchangeable Mn, but in a poorer correlation between MnAAAc-EDTA and reducible Mn. The pH-corrected MnAAAc-EDTA indices or exchangeable Mn explained the variation in the Mn content of the first ryegrass yield to a higher degree (R2 = 33—38 %) than did the original indices (R2 = 3 %). However, the original indices explained 38—55 % of the variation in the Mn content of subsequent ryegrass yields, whereas the pH-corrected indices explained only 16—34 % of the variation. Thus, MnAAAc-EDTA is an indicator of the potentially plant-available reserves of Mn, while the pH-corrected indices reflect the quantity of the readily available Mn in the soil.