Most terrestrial plants grow in soil. Soils provide:
Mechanical support
Mineral nutrients and water from the soil solution
O2 for root respiration
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Soils also harbor many bacteria and other organisms; some of these are beneficial to plant life, but others are harmful. Some soils contain toxic levels of metal ions such as cadmium, chromium, and lead.
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Soil can vary greatly in its composition of particles and nutrient availability (fertility). Most soils consist of three major horizons.
Uptake of minerals that exist as cations in soil water is facilitated by a cation exchange process under slightly acidic pH conditions.
The fertility of depleted and leached soils can be improved by adding organic and inorganic fertilizers.
Soils are modified by natural phenomena such as rain, temperature extremes, and the activities of plants and animals. They are also modified by the activities of people, particularly in agriculture. In this section you’ll learn about the composition, structure, and formation of soils, as well as their role in plant nutrition.