Agriculture Reference
In-Depth Information
5
Plant Nutrition
ESSENTIAL ELEMENTS
Plants require 13 essential elements for their growth. In addition to these
13 nutrients they utilize carbon, hydrogen, and oxygen, which come from
water and the atmosphere. The 13 essential elements are categorized in
two groups: (1) those needed in relatively large amounts, termed major or
macroelements; and (2) those consumed in relatively small amounts, which
are called micro or trace elements. The macroelements include nitrogen
(N), phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), and
sulfur (S). The microelements are iron (Fe), manganese (Mn), copper (Cu),
boron (B), zinc (Zn), molybdenum (Mo), and chlorine (Cl). Plants cannot
live without any one of these elements, hence the term “essential.” We as
growers must provide all of these 13 nutrients to the plant. In hydroponics
they are all added in the nutrient solution.
I often encounter the argument that hydroponic plants are not “organic”
because in hydroponics you use fertilizer salts. My reply is that all plants
are organic as they only use inorganic ions in their uptake of these ele-
ments to grow. The plants manufacture the organic materials of their
makeup through photosynthesis. “Organic gardening” is often confused
with the fact that in most cases it indicates that only natural bioagents are
used to control pests rather than synthetic pesticides. As a result, organic
products should really be termed “pesticide free.”
SOIL IN COMPARISON TO HYDROPONICS
Soil has both organic and inorganic components. The organic part is the
humus consisting of dead plant and animal matter. The inorganic com-
ponent is the sand, gravel, and rock that must be weathered to release its
inorganic elements. The organic material undergoes decomposition by
numerous soil organisms and animals. This releases its inorganic elements
into the soil water. The released inorganic elements into the soil water give
us the soil solution. This soil solution comes in contact with the plant roots
where the individual elements in their atomic state are taken up through a
process of electrical and chemical potential difference between the inside
and outside of the root membrane (Figure 5.1).
In hydroponics we add all of these essential elements from highly pure
fertilizer salts. They dissolve in water releasing their individual elements
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