Soil Acidity
Soil acidity is measured using the pH scale. Most soils fall into the range between 4 to 8, although some fall are extremely acidic or basic. One example is the Pygmy Forest in Mendocino County, California. Its soils have a pH of 2.8 to 2.9 (very acidic!) while in Death Valley, California, the soil has a pH of 10.5 (very basic).
Soil pH is very important to plants. Certain minerals cannot dissolve in water with differences in pH. At a low pH, aluminum and manganese in soil water are more soluble and the roots of plants can absorb them in toxic concentrations. Calcium phosphate, becomes less soluble and less available to plants as the pH rises. Soil pH also affects the leaching of nutrients. In acidic soil, the negatively charged soil cannot bind as easily to positively charged minerals. As a result, those minerals are washed to lower horizons. For example, potassium, which is essential for plant growth, is leached more readily from acidic soil.
The optimum pH for plant growth is 6.0 to 7.0 because most nutrients needed by plants are available in that pH range.
Soil pH can be affected by plants and the organisms in the soil. Leaf litter of conifers contains acids that leach into the soil lowering its pH. The decomposition of humus and the cellular respiration of organisms (remember carbonic acid?) also decrease the pH of soil.
Hydrangea are a type of flower whose color is determined by the pH of the soil. Acidic soil produces a pink flower while alkaline (basic) soil produces blue flowers. It acts as a type of litmus paper!
Soil pH is very important to plants. Certain minerals cannot dissolve in water with differences in pH. At a low pH, aluminum and manganese in soil water are more soluble and the roots of plants can absorb them in toxic concentrations. Calcium phosphate, becomes less soluble and less available to plants as the pH rises. Soil pH also affects the leaching of nutrients. In acidic soil, the negatively charged soil cannot bind as easily to positively charged minerals. As a result, those minerals are washed to lower horizons. For example, potassium, which is essential for plant growth, is leached more readily from acidic soil.
The optimum pH for plant growth is 6.0 to 7.0 because most nutrients needed by plants are available in that pH range.
Soil pH can be affected by plants and the organisms in the soil. Leaf litter of conifers contains acids that leach into the soil lowering its pH. The decomposition of humus and the cellular respiration of organisms (remember carbonic acid?) also decrease the pH of soil.
Hydrangea are a type of flower whose color is determined by the pH of the soil. Acidic soil produces a pink flower while alkaline (basic) soil produces blue flowers. It acts as a type of litmus paper!