Acid precipitation depletes soil cations by ion exchange— the large number of protons in that precipitation causes the cations needed by plants to leave soil particles and become solubilized. They can then be washed out of the soil as water drains from it. This could be tested by applying precipitation of various pHs, from basic to acidic, as well as neutral.
Work Step by Step
See Fig. 37.3 for an idea of how cations are “loosened up” from the soil by protons in acidic water. Apply that same concept to a large amount of protons in a given volume of water. Since pH is the key issue, testing the effects of various pHs is one obvious way to test this, though not the only one.