Guest Columnist
I recently had a discussion with someone who had amended his heavily acidic garden soil to get the pH up to around 5.4. My thought was how long it would take before the soil began reverting to its original pH. We can amend soil to change the pH, but after an unknown amount of time, the soil will begin reverting to its original pH.
For those with heavily acidic soils, pH is a limiting factor on what can be planted for garden crops. A pH of 5.4, for example, would limit the production of tomatoes and peppers, but would be good soil for blueberries. For those who choose to do so, soils can be amended (with lime for example) to raise the pH more toward 6.5-7.0, but do so in stages; not all at once! Then, the question remains one of how long the amended soils will last? The answer, due to a myriad of possibilities, is usually unknown.
To a large extent, the answer lies in the amount of rainfall. Raindrops can pick up infinitesimally tiny amounts of carbon as they fall thus becoming a very weak carbonic acid, which would over many, many years, slightly lower pH. This is a very weak acid and really has only a tiny effect on acid soils, and virtually none on alkaline soils. If, however, the clouds contained sulfur, the newly formed acid rain would change things much faster.
The real effect however is in the leaching of the amendments, regardless of whether the soil is acidic or alkaline. As the water drains down through the soil, it takes part of the amendment with it, thus raising or lowering the soil toward its original pH. Additionally, heavy crop yields lower the pH by draining the minerals which have kept it in balance.
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