Dyes

Redox measurements are valuable to predict the occurrence/likelihood of a reduced species in soil solution, e.g., the presence of ferrous Fe (Fe²⁺). One simple method to infer reducing conditions is the use of dyes, which react with Fe²⁺ to colored compounds. Commonly, 2,2’-dipyridyl Childs 1981 is taken but potassium ferrocyanide Ringrose_voase and Humphreys 1993 can also be used. Although simple to use, this method provides only a snapshot, and it also uses harmful chemicals. Childs (1981) proposed using a 0.1% solution of α,α-dipyridyl and the NTCHS a 0.2% solution within 1 M ammonium acetate (Fiedler et al. 2007). The solution can be sprayed or dripped onto the soil of a soil auger or towards the front of a soil profile. Typically, the reaction occurs very fast within seconds.

When using the dye you should hurry up and do it on a fresh sample since Fe²⁺ will auto-oxidize and metal containing auger or steel cylinder might deliver a false positive reaction.