Agriculture Reference
In-Depth Information
How are these used? Since cations are electrostatically bonded to soil particles, they are
Through a process in the root hairs, ionic nutrients are released into the soil solution where
they then become available for use.
Because clay soils tend to have more organic matter present than sandy soils, the CEC
value of clay tends to be higher than that of sand. Increasing the organic matter content of
as topsoil disappears due to erosion and other factors, our soils have smaller amounts of
organic matter. As a result, modern topsoils have fewer nutrients available than topsoils
containing rich amounts of humus 1 .
As plants draw nutrients out of the soil solution, more may be released into the solution
from exchange sites present on clay and humus particles. When chemical fertilizers are
added to soil, they aren't necessarily directly used by plants. Instead, like minerals from
other sources, they become attached to exchange sites. Once they are situated within the
soil mass, they are then consumed by microorganisms which transform them into forms
that can be absorbed by plant roots 2 .
inside the plant. Note that the cells and extracellular fluid within the roots themselves
have a higher concentration of nutrients used to sustain the plant's life compared to
the concentration present in the soil. To get around this “ concentration gradient that
would normally prevent soil-based nutrients from getting inside of the roots, a number
of electrochemical and biophysical processes (e.g. ion pumps ) are used to bring these
substances in. Once inside, they are transported throughout the plant. These processes will
be covered in more detail later on.
Since nutrients are typically bound to soil particles, plant roots extract nutrients through
three main mechanisms:
• The root grows into an area where the soil solution has not been depleted of
nutrients and starts absorbing nutrients from the soil particles via fine root hairs.
• Whenarootdepletesthenutrientsnearit,additionalnutrientsoftendiffuseintothe
deficient area, depending upon the moisture level and the nature of the soil.
• Or, through mass flow, like after a rain shower, water flows towards the root and
carries nutrients towards it.
In summary, the fertility of soil is affected by a number of factors:
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