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2. Soil Fundamentals
Nitrogen is used in cells to build proteins, DNA, and chlorophyll. Nitrogen
exists in abundance in the atmosphere, but not in a form usable by plants.
Special nitrogen-fixing soil bacteria exist that are often associated with
legumes (beans and peas). These bacteria can convert atmospheric nitrogen
into a form that can be used by plants and other soil microorganisms. Nitrogen
can also be added to soils in inorganic forms, such as urea, ammonia, and
nitrate. Organic amendments, such as manure and compost, are good ways to
add nitrogen to soil. Soil microbes may compete with plants for the nitrogen in
the soil, for example if a carbon-rich amendment such as sawdust is added to
the soil.
Phosphorus is used in cells as a component of DNA and membranes,
and for energy storage.
Potassium is essential for the chemical reactions that keep plants and
microorganisms alive; specifically, it activates enzymes (proteins that are
responsible for life’s chemical reactions). It is also a large component of the
liquid in cells, and thus it interacts with changes in water availability, helping
both plants and microorganisms deal with environmental stressors.
Calcium is a major component of cell walls and is therefore needed in large
quantities in the growing parts of plants—roots and shoot tips, fruits,
and unfolding leaves and petals.
Magnesium is a major component of the chlorophyll molecule and thus
essential for photosynthesis. It is also involved in the making of oils and
proteins, and in enzyme activation.
Sulfur is a component of DNA, proteins, vitamins, and oils.
Iron is needed for enzymes that aid in making nitrogen available in
a usable form for plants, and in chlorophyll formation.
N
P
K
Ca
Mg
S
Fe