Plant nutrition
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Plant nutrition is the study of the chemical elements that are necessary for plant growth. There are several principles that apply to plant nutrition.
Some elements are essential, meaning that the absence of a given mineral element will cause the plant to fail to complete its life cycle; that the element cannot be replaced by the presence of another element; and that the element is directly involved in plant metabolism (Arnon and Stout, 1939). However, this principle does not leave any room for the so-called beneficial elements, whose presence, while not required, has clear positive effects on plant growth.
Plants require specific elements for growth and, in some cases, for reproduction.
The mnemonic for the elements essential to plant growth is:
CHOPKN'S CaFe Mg MoB CuMnZn
or
C-Hopkins Cafe. Mighty Good. Mob comes in.
Major nutrients include:
C = Carbon 450,000ppm
H = Hydrogen 60,000ppm
O = Oxygen 450,000ppm
P = Phosphorus 2,000ppm
K = Potassium 10,000ppm
N = Nitrogen 15,000ppm
S = Sulfur 1,000ppm
Ca = Calcium 5,000ppm
Fe = Iron 100ppm
Mg = Magnesium 2000ppm
Minor Nutrients:
Mo = Molybdenum 0.1ppm
B = Boron 20ppm
Cu = Copper 6ppm
Mn = Manganese 50ppm
Zn = Zinc 20ppm
Cl = Chlorine 100ppm
Concentration of ppm (parts per million) represents the dry weight of a representative plant.
Additional elements include nickel and silicon, whose requirements are vague for all but a very few select plants. Cobalt has proven to be beneficial to at least some plants, but is essential in others, such as legumes where it is required for nitrogen fixation. Selenium and sodium may also be beneficial.
Plant nutrition is a difficult subject to understand completely, partially because of the variation between different plants and even between different species or individuals of a given clone. Elements present at low levels may demonstrate deficiency, and toxicity is possible at levels that are too high. Further, deficiency of one element may present as symptoms of toxicity from another element, and vice-versa.
Green plants obtain their carbohydrate supply from the carbon dioxide in the air by the process of photosynthesis.