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.

Nutrient availability for soil pH levels
University of Missouri Extension Service

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 the pH is between 6.3 and 6.8.
So why is this important?
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