Simple tests for the assessment of aluminium and manganese levels in acid soils

Abstract

Alkaline formaldoxime and a reagent mixture based on pyrocatechol violet in ammonium acetate were found to be the best of several reagents tested for ranking the concentrations of manganese (Mn) and aluminium (Al), respectively, in solutions absorbed by filter paper strips. The concentrations of these metals in soil suspensions, 1:1 (vh) in 0.01 mol L-1 calcium chloride, were estimated by obtaining clean samples on test strips of filter paper and visually comparing the colours produced with the above reagents against those formed using standard solutions of known Mn and Al concentrations. The test values when compared with analytical values for the filtered suspensions showed that acid soils can be readily ranked into groups. Each group is defined by a given range of Mn or Al levels. The reagents, sampling procedure and colour development have many advantages suited to a field test for characterising the A1 and Mn levels of acid soils.