While a soil test involves many important nutrients, the pH
level is critical in optimizing the microbial activity in the
root zone. This is especially important for organic gardeners
because a proper pH will allow critical nutrients to be released
as the plants mature. As you can see in the chart, there’s a
fall off of phosphorus availability as pH declines (or becomes
more acidic – moving to the left on the chart). Root growth is
dependent on adequate levels of phosphorus. We can also see how
acidity affects other critical metals such as calcium and
magnesium when pH drops below neutral (pH 7). These are among
the macronutrients frequently cited as deficient in soil tests.
But altering pH can be difficult. Clay soils generally have a
high degree of buffer capacity, meaning that the soil is
resistant to change. Adding organic matter to the soil also
increases both the buffer capacity and the acidity of the soil.
While plants do well in soils ranging from a pH of 6 to 6.5,
peak microbial activity occurs when