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Basic Botany

  MG Manual Reference
Ch. 1, pp. 39 - 41

Nitrogen (N)

Absorbed as NO3-, NH4.
Leaches from soil, especially NO3-.
Mobile in plant.

Nitrogen excess:

Succulent growth, dark green color, weak spindly growth, few fruits, may cause brittle growth especially under high temperatures.

Nitrogen deficiency:

Reduced growth, yellowing, reds and purples may intensify with some plants, reduced lateral bud breaks. Symptoms appear first on older growth.

Action notes:

In general, the best NH4/NO3- ratio is 1:1.
High NH4 under low sugar conditions can cause leaf curl.
Uptake inhibited by high P levels.
N/K ratio extremely important. Indoors, best N/K ratio is 1:1 unless light is high.
In soils where large amounts of organic matter are added the carbon:nitrogen ratio is increased and supplemental N should be supplied to aid in the breakdown of the carbon material.

Phosphorus (P)

Absorbed as H2PO4-, HPO4-.
Does not leach from soil readily.
Mobile in plant.

Phosphorus excess:

Shows up as micronutrient deficiency of Zn, Fe, or Co

Phosphorus deficiency:

Reduced growth, color may intensify, browning or purpling in foliage in some plants, thin stems, reduced lateral bud breaks, loss of lower leaves, reduced flowering.

Action notes:

Rapidly "fixed" on soil particles when applied under acid conditions fixed with Fe, Mg and Al.
Under alkaline conditions fixed with Ca.
Important for young plant and seedling growth.
High P interferes with micronutrient absorption and N absorption. Used in small amounts when compared to N and K. May leach from soil high in bark or peat.

Potassium (K)

Leaches from soil absorbed as K+.
Mobile in plant.

Potassium excess:

Causes N deficiency in plants and may affect the uptake of other positive ions.

Potassium deficiency:

Reduced growth, shortened internodes, marginal burn or scorch (brown leaf edges), necrotic (dead) spots in the leaf, reduction of lateral bud breaks and tendency to wilt readily.

Action notes:

N/K balance is important.
High N/low K favors vegetative growth; low N/high K promotes reproductive growth (flower, fruit).

Magnesium (Mg)

Absorbed as Mg++.
Leaches from soil.
Mobile in plant.

Magnesium excess:

Interferes with Ca uptake.

Magnesium deficiency:

Reduction in growth, marginal chlorosis, interveinal chlorosis (yellow between the veins) in some species. May occur with middle or lower leaves, reduction in seed production, cupped leaves.

Action notes:

Mg is commonly deficient in foliage plants because it is leached and not replaced. Epsom salts at a rate of 1 teaspoon per gallon of water may be used 2 times a year. Mg can also be absorbed by leaves if sprayed in a weak solution. Dolomitic limestone can be applied in outdoor situations to rectify a deficiency.

Calcium (Ca)

Moderately leachable.
Absorbed as Ca++.
Limited mobility in plant.

Calcium excess:

Interferes with Mg absorption. High Ca usually causes high pH which then precipitates many of the micronutrients so that they become unavailable to the plant.

Calcium deficiency:

Inhibition of bud growth, death of root tips, cupping of maturing leaves, weak growth, blossom end rot of many fruits, pits on root vegetables, apples, and pears.

Action notes:

Ca is important in controlling pH and is rarely deficient if the correct pH is maintained. Water stress, too much or too little, can affect Ca relationships within the plant causing deficiency in the location where Ca was needed at the time of stress.

Sulfur (S)

Absorbed as SO4-.
Not mobile.

Sulfur excess:

Sulfur excess is usually in the form of air pollution.

Sulfur deficiency:

S is often a carrier or impurity in fertilizers and rarely deficient. It may be also absorbed from the air and is a by-product of combustion. Symptoms are a general yellowing of the affected leaves or the entire plant.

Action notes:

Sulfur excess is difficult to control.

See also Micronutrient Outline and general information on plant nutrition.

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