Chemical properties of soils affect nutrient availability to plants and soil acidity. Eighteen elements have been shown to be essential to the growth of plants. Some are considered macronutrients because they are used in relatively large amounts. Others are considered micronutrients because they are used in relatively small amounts. The macronutrients are carbon, hydrogen, and oxygen, which come from air and water. Nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur come mostly from soil constituents. To maintain healthy, productive soils, these nutrients may need to be added to the soil for optimum plant growth. Nitrogen, phosphorus, and potassium are normally applied to soil in most standard fertilizers. Calcium and magnesium are applied to soil in liming products. The burning of fossil fuels adds sulfur and nitrogen to the air, so they come back to the Earth with precipitation. Organic matter helps to hold these nutrients in the soil and releases them slowly.

One very important chemical property of soils is acidity. Acidity is usually evaluated by pH. Low pH values mean high soil acidity, while high pH values mean low soil acidity. Most plants grow best with pH values between 5.0 and 7.0.


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