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Objectives - Soil Science

Soil deformation by heavy machinery results in a compactionof the aggregates leading to aeration deficiencies. Among other things such changes cause deficiencies of oxygen in the top soil. Therefore, the aerobic environment changes to an anaerobic one and oxygen is not longer available as electron acceptor. Due to this anaerobiosis the microorganisms are obliged to use other electron acceptors like trivalent iron. As a result, iron mottles and bleaching zones can be verified in the top soil.
To detect ferrous iron 2,2'-dipyridyl reagent is added to a soil sample (BARTLETT, 1998). A red or pink colour indicates the presence of this reduced species.

Abb. 1: Reaktionsgleichung und Farbumschlag (Bipyridin)
Fig. 1: Chemical reaction and red colour of the complexe
 

Additionally, BARTLETT (1998) described two other tests (Tetramethylbenzidine Oxidation, Chromium Oxidation) reacting with manganese oxides. The resulting colour indicates the redoximorphic state of the soil.

Soil physical parameters, e.g. relative apparent gas diffusion coefficient, concentration of carbondioxide or bulk density, are indicators for soil deformation. The parameters are obtained as scale types for the chemical tests.