Practice exam #3 - QUESTION 2

a) The reason for that kind of parent material end up with having very low pH is iron sulfide would have the chemical reaction (oxidation). When the soil is unsaturated or drained it reacts with oxygen and releases hydrogen to lower the pH.

b) First: keep the soil saturated Second: add basic ion (C, Mg, K, Na)

Oxidation of pyrite (or iron sulfide) produces soil pH of 3 or 3.5. Hence, to bring such low pH to something that most plants can tolerate (around at least pH 5) would require large quantities of lime (or any other material that would contain Ca and/or Mg) and frequent applications of that material would be needed. Pls note that we do not want to add material containing sodium because of sodium's negative effect of aggregate formation. Sodium is a bad news for soils ;-)