Land plants live anchored in the soil and obtain water and mineral nutrients from it. Soils are complex in structure and vary in fertility. Farmers can add fertilizers to improve the nutrient contents of soils.
learning outcomes
You should be able to:
Predict changes in a soil in response to environmental and land use changes.
Explain how soil fertility is influenced by the process of cation exchange.
Compare and contrast organic and inorganic fertilizers.
Soils are dynamic systems. What changes might result when land is subjected to heavy irrigation for agriculture after being relatively dry for many years? What changes in the soil might result when a deciduous forest is cut down and replaced by crops that are harvested each year?
Heavy irrigation after a prolonged dry period may produce runoff of topsoil (the A horizon) and leaching of ions (especially anions) into the subsoil, making fewer nutrients available to plant roots. Converting land use from virgin deciduous forest to crops will change the composition of living organisms in the soil, as many organisms that live in association with tree roots will disappear. The soil structure and texture will also change, because roots will no longer be present to hold the soil together and make air spaces. The soil chemistry will change, because crops take up nutrients from the soils and the nutrients are removed from the system when the crops are harvested.
How does the process of cation exchange enhance soil fertility?
Cation exchange frees ions bound to soil particles into the soil solution, where they can enter plant roots.
What are the differences between organic and inorganic nitrogen fertilizers in terms of plant nutrition?
There are no differences between organic and inorganic nitrogen fertilizers in terms of plant nutrition; both enter the plant root as nitrate NO3–.
Thus far we have focused on the uptake of nutrients in the soil by plant roots. An understanding of how plants acquire nutrients from the soil would be incomplete, however, without taking into account the involvement of soil microbes, including fungi and bacteria. In the next section we will focus on the intimate interactions of plants with these organisms, which are essential to the success of most terrestrial plants.