It is important to note that the pH
scale is a logarithmic scale, meaning that each whole number is a factor of 10
larger or smaller than the one next to it. For example, a soil with a pH of 9.5
is ten times more alkaline than a soil with a pH of 8.5 and 100 times more
alkaline than a soil with a pH of 7.5!
Acidic soils are common in areas with abundant rainfall, especially east of the Mississippi and the Pacific Northwest; pockets of acidic soil can occur in other places. In acidic soils, nutrients dissolve slowly or not at all. Critical plant nutrition is locked up in insoluble mineral compounds that plants cannot utilize. Fertilizer is of little use in acidic soils because it cannot be absorbed.
To correct high acidic levels in soil, add ground agricultural limestone; try to keep to manufacturer recommendations. The limestone replaces the calcium and magnesium in the soil that rain washes away; it effectively raises the pH of acidic soil. Also try keeping the soil amended with large amounts of organic matter to help increase the soil’s buffering capacity (ability of the soil to resist a change in the pH) and the plants ability to tolerate levels of acidity.
Alkaline soils are defined as soil with a pH level of over 7 and more common in the Western states that experience less rainfall. It is important to stress though that geography and rainfall aren’t absolute indicators of soil pH levels. Using liquid seaweed or another foliar spray is helpful in managing this problem. Adding well-decomposed organic matter, such as compost, gypsum, powdered sulfur or acidifying plant food, can help correct soil with a high pH. It is important to test your soil because high pH levels can also indicate high levels of sodium in the soil that can also negatively affect plant growth.