PLANT NUTRIENTS

Barbara J. Bromley, Mercer Co. Horticulturist 04

 

All living things need sources of nutrients. For some plants they may come from eroding rocks, decomposing plant and animal matter and other naturally occurring sources. To make sure the plants in our gardens have enough of necessary nutrients, we often add them as fertilizers.

One common question is why trees and shrubs in the woods, which are never fertilized by humans, manage to survive for decades with little obvious stress, yet the trees and shrubs in our yards die or decline quickly if not fertilized with some regularity. The answer is that we tend to clean up our residential properties by putting grass clippings, dead petunias, leaves, needles, twigs, and branches out at the curb for pickup and retire dead animals and birds to the trash. In nature all of these things plus bird droppings and dead insects decompose and release their stored nutrients back to the soil. The compost that is produced in some back yards will return many vital nutrients to the soil, but may still have to be supplemented with fertilizers.

The primary elements carbon (C), hydrogen (H), and oxygen (O) make up all living things and occur abundantly in nature. Nitrogen (N), phosphorus (P), and potassium (K), the primary nutrients, do not occur in great enough quantity, and are the major components of most commercially prepared fertilizers. When all three are present in a fertilizer (10-6-4 or 24-6-12, for example) it is said to be "complete."

Muriate of potash (0-0-60) is an example of a single nutrient fertilizer.

The secondary nutrients, calcium (Ca) and magnesium (Mg) are added to soils as ground, granular, or pelletized dolomitic or calcitic limestone. Sulfur (S) occurs naturally and is seldom deficient.

The minor or trace elements include boron (B), iron (Fe), manganese (Mn), copper (Cu), molybdenum (Mo), chlorine (Cl), and zinc (Zn) and are needed in very low amounts. They are usually naturally available. When they need to be added, they are found in trace element compounds, as individual elements, and in organic fertilizers, such as seaweed extract.

On a fertilizer container, the percentages of available major nutrients are listed as three numbers, such as 10-6-4, 5-10-5, or 0-46-0. These numbers indicated the percentage by weight of total nitrogen, phosphorus, and potassium (in that order) from sources listed on the container or bag. The remainder of the contents (to add up to 100%) is ground corn cobs, clay pellets, or other carrier to make the fertilizer easier to spread. Occasionally a fourth number is added which would be specified as either sulfur or iron (i.e. 22-9-5-2.)

Garden fertilizers: 5-10-5, 10-10-10, 5-10-10, 8-8-8, 15-30-15, etc.

Lawn fertilizers: 27-3-3, 10-6-4, 20-10-10, 34-0-0, 34-4-8, etc.

Fertilizers may be obtained based on the ratio of nutrients. A 5-10-5, a 15-30-15, and an 8-16-8 all have a 1-2-1 ratio. 24-6-12 and 36-9-18 are 4-1-2 ratio materials. At different application rates, fertilizers with the same ratio would deliver the same relative amounts of the three primary nutrients.

Nutrient needs of plants vary. Phosphorus and potassium percentages are determined by need based on soil test result and the plant to be grown. Nitrogen alone is the nutrient on which the application rate is based. Lawns generally need about 1 lb. of actual N per 1000 square feet (SF) per application. Application rate is determined by dividing the first number of the fertilizer analysis into 100. The result is the rate. ie: 10-6-4 is applied at 10 lb./1000 SF, 10-10-10 @ 10 lb./1000 SF, 20-6-10 @ 5 lb./1000 SF, 33-0-0 @ 3 lb./1000 SF, and 24-6-12 @ 4 lb./1000 SF. Vegetable and flower garden spring application is generally 2 lb. of N/1000 SF, so rate is determined by dividing the first number on the fertilizer into 100, then doubling it.

Deficiencies and excesses can occur under a variety of conditions, including heavily cropped land, grass clipping removal on turf, very high or low pH, leached sandy soil, highly organic muck soils, and when other nutrients are in excess. Generally, the way to be sure an excess or deficiency exists is to have a soil or plant tissue test run. "Self-doctoring" without test results can compound a problem. Excesses can occur just as easily with organic and rock powder fertilizers as with synthetic nutrient sources if they are over-applied without soil test recommendations.

The following nutrient list includes the function of the nutrient in plants, its mobility in the soil and in plants, and deficiency and excess symptoms. Not all of the symptoms will generally occur at one time or even in all plants. There are many types of plants (conifer, deciduous, broad-leaved evergreen, grass, herbaceous) with different expressions of deficiency or excess.

MACRONUTRIENTS

(Needed by plants in relatively large amounts)

NITROGEN (N)

Function of Nitrogen

Imparts dark green color to plants

Promotes leaf and stem growth

Influences crispness and quality of leaf crops

Stimulates rapid early growth

Increases protein content of food crops

Feeds soil microorganisms as they decompose organic materials

• Nitrogen is mobile in plants. The mobility in soil is dependent on the chemical form of the element used. Leaches from soil fairly readily.
• Organic N is not available to plants until it has been converted to an inorganic form by soil bacteria.
• High phosphorus levels inhibit uptake.
• N/K ratio is important: high N/low K favors vegetative growth; low N/high K promotes flowering and fruiting.

Nutrient deficiency symptoms - Nitrogen

• Small pale yellow leaves
• Plant may be light green. Older leaves affected first.
• Slow, stunted growth
• Drying up ("firing") of leaves starting at bottom of plant (In corn, grasses, and grain firing starts at tip of bottom leaf and proceeds down center or along midrib)
• Turf: light green or yellow green leaves; may start dying at tips

Nutrient excess symptoms - Nitrogen

Dark green leaf color

Excessive growth

Retarded maturity

Loss of buds or fruit

Sources of N

Nitrates: ammonium nitrate, potassium nitrate, and sodium nitrate

Ammonia: ammonium nitrate, ammonium sulfate, anhydrous ammonia,

Synthetic organics: calcium cyanamide, urea

Natural organics (animal): blood meal, tankage, fishmeal, fish emulsion, manure

Natural organics (vegetable): cottonseed meal, soybean meal, castor pomace

PHOSPHORUS (P)

Function of Phosphorus

Stimulates early root formation and growth

Hastens maturity of crops

Stimulates blooming

Aids in seed formation

Gives winter hardiness to fall-seeded grains and hay

Promotes rapid and vigorous start to plants

• Phosphorus is very mobile in plants; relatively immobile in soil, and does not leach.
• Stored in seeds and fruit.
• Is most readily available to plants between a pH of 6 and 7.5 (unavailable in very acid or alkaline soils).
• Found in greatest concentration in sites of new cell growth.
• Phosphorus absorption is reduced at low soil temperatures, especially in early spring.

Nutrient deficiency symptoms - Phosphorus

• Purplish or reddish color on leaves (especially undersides,) stems, and branches
• Cell division retardation
• Slow growth and maturity
• Small slender stalk (corn)
• Low yields of grain, fruit, and seed
• Turf: thin sod; thin, curled leaves; dusky blue-green with purple tint in cool weather

Nutrient excess symptoms - Phosphorus

Possible tie up of other essential nutrients

Sources

Super phosphate

Rock phosphate

Bone meal

Ammonium phosphate

POTASSIUM (K)

Function of Potassium

Promotes increased vigor and disease resistance in plants

Imparts winter hardiness to legumes and other crops

Stimulates production of strong stiff stalks (reduces lodging)

Increases plumpness of grains and seeds

Aids in protein production

Improves quality of crop yield

Helps development of root system

Essential to starch, sugar, and oil formation and transfer

• Potassium, available as potash (K2O), is highly mobile in plants, and generally immobile in soil.
• Tends to leach.

Nutrient deficiency symptoms - Potassium

• Mottling, spotting, streaking or curling of leaves, starting on lower levels
• Bronzing and dying of leaf margins
• Some spotting between leaf veins
• Leaves may be chlorotic with brown spots throughout
• Lower leaves scorched or burned on margins and tips
• Reduced vigor
• Premature leaf loss
• Susceptibility to diseases
• Thin skin and small fruit
• Turf: yellow tips on leaves; may turn brown and die at tips

Nutrient excess symptoms - Potassium

Coarse, poor colored fruit

Reduced absorption of Mg and Ca

Sources - Potassium

Muriate of potash (potassium chloride)

Muriate of sulfur (potassium sulfate)

Sul-po-mag (sulfate of potash magnesia)

Greensand

Wood ashes

Seaweed

 

CALCIUM (Ca)

Function of Calcium

Part of cell walls, part of enzymes

Promotes early root formation and growth

Improves general plant vigor and stiffness of straw

Influences intake of other plant nutrients

Neutralizes poisons produced in the plant

Encourages grain and seed production, increases calcium content of food and feed crops

• Calcium is immobile in plants, and relatively immobile in soil.
• Moderately leachable.
• Sometimes difficult to differentiate between calcium deficiency and magnesium toxicity.

Nutrient deficiency symptoms - Calcium

• Young leaves in terminal bud become "hooked" and die back at tips and along margins
• Leaves appear wrinkled
• Young leaves may remain folded
• New leaves yellow, while older leaves are dark green
• Light green band along leaf margin
• Short and much-branched roots
• Causes blossom end rot in tomato
• Turf: reddish-brown leaves; may curl, then die

Nutrient excess symptoms - Calcium

Reduced intake of K and Mg

Sources of Calcium

Limestone

Basic slag

Gypsum

Oyster shells

Phosphate rock

MAGNESIUM (Mg)

Function of Magnesium

Is an essential part of chlorophyll

Regulates uptake of other plant nutrients

Acts as a phosphorus carrier in plants

Promotes formation of oils and fats

Plays a part in the translocation of starch

Necessary for formation of sugar (aids photosynthesis)

• Magnesium is mobile in plants, mobile in acid soils, and fairly immobile above pH 6.5.
• Leaches from soil.

Nutrient deficiency symptoms - Magnesium

• Mottled yellowing between veins of older leaves, veins remain green, yellow areas may brown and die
• Loss of yield
• Chlorosis of older leaves
• Weak stalks with long branched roots
• Leaves curve upward along margin
• Turf: yellow stripes on leaves, turning red

Nutrient excess symptoms - Magnesium

Reduced absorption of Ca and K

Sources of Magnesium

Magnesium sulfate (Epsom salts)

Dolomitic limestone (is 1/3 Mg carbonate)

 

SULFUR (S)

Function

Helps to build proteins

Promotes increased root growth

Promotes nodule formation on legumes

Helps maintain dark green color

Stimulates seed production

Encourages vigorous plant growth

• Sulfur is mobile in plants, somewhat immobile in soil.
• Organic sulfur is converted into available sulfate sulfur by soil bacteria.
• Leachable.
• It is rarely deficient, but when deficiency occurs, is most likely on sandy, low-organic soils.

Nutrient deficiency symptoms

• Plant as a whole becomes light green, looks like nitrogen deficiency
• Turf: yellow leaves

Nutrient excess symptoms

Sulfur burn from too low pH

Sources

Sulfur

Superphosphate

 

MICRONUTRIENTS

(Needed by plants in trace amounts)

BORON (B)

Function of Boron

Affects absorption of other elements

Affects germination of pollen tube

• Boron is extremely immobile in plants and is not translocated to new growth, but moves readily in soil.
• Deficiencies often occur when pH is between 6.0 and 7.5, on deep sandy soils, and when high rates of N, K, and Ca are used.
• Deficiency more apparent during drought stress.

Nutrient deficiency symptoms - Boron

• Youngest leaves become light green and may be distorted, small leaves
• Terminal bud may eventually die, may have multiple buds
• Heart rot and corkiness
• Deficiency diseases include brown rot of cauliflower, heart rot of turnip, yellow top of alfalfa, corky core of apple, blackheart of beet
• Turf: slow growth; pale green tips; bronze tint

Nutrient excess symptoms - Boron

Leaves turn yellowish red

Sources

Borax

 

IRON (Fe)

Function of Iron

Aids in prevention of chlorosis

Needed for chlorophyll

• Iron is immobile in plants.
• Mobility decreases in soil with increasing pH.
• Deficiencies can be corrected by lowering pH.
• Excessive P may induce deficiency of Fe

Nutrient deficiency symptoms - Iron

• Chlorosis (yellowing or whitening of leaves, veins remain green)
• Turf: pale leaves, turning yellow

Nutrient excess symptoms - Iron

None known

Sources

Iron sulfate

Chelated iron

MANGANESE (Mn)

Function of Manganese

Increases availability of Ca, Mg, and P

Necessary for chlorophyll synthesis and photosynthesis

• Manganese is immobile in plants.
• Mobility in soil decreases with increasing pH.
• Soils very high in organic matter or poorly drained are deficient at pH 5.8 to 6.5. For other soils, deficiency usually occurs between pH 6.5 and 8.0, especially where soil has been heavily limed.

• Toxic in very acid soil.
• Excessive water, poor aeration, and excess heavy metals influence Mn uptake.

Nutrient deficiency symptoms - Manganese

• Mottled chlorosis of leaves
• Stunted growth
• Pale green to yellow and red color between green veins of tomato and beet leaves, chlorosis of spinach and soybeans on overlimed soil, gray speck on oats
• Turf: small distinct yellow or dead spots on leaves; withered drooping leaf tips

Nutrient excess symptoms - Manganese

Small dead areas in leaves with yellow areas around them

Sources

Manganese sulfate (tecmangam)

COPPER (Cu)

Function of Copper

Enzyme activator

• Relatively immobile in soil and plants.
• Deficient more often in organic than mineral soils, and more often in sandy than heavy soils.
• Deficient at high pH.

Nutrient deficiency symptoms - Copper

• Young leaves may be permanently wilted without any yellowing
• Multiple budding
• Gum pockets

Nutrient excess symptoms- Copper

Prevents uptake of iron

Causes stunting of roots

Blasting of onions and truck crops on muck or other very highly organic soils

Turf: yellow and stunted leaves, tips die, bluish discoloration at youngest leaf tips

Sources

Copper sulfate

Neutral copper

MOLYBDENUM (Mo)

Function of Molybdenum

Helps in the utilization of N

• Molybdenum is mobile in plants and in soil.
• It is less available at a lower pH. Generally no deficiency over pH 6.0.
• Acid leached (forest) and sandstone soils generally low in Mo.

Nutrient deficiency symptoms - Molybdenum

• Narrow leaves with interveinal yellowing on older leaves
• New leaves green at first becoming mottled as they expand
• Symptoms in plants vary greatly
• Turf: mottled yellow and withered leaves, stunting

Nutrient excess - Molybdenum

Poisonous to livestock

Sources

Sodium molybdate

ZINC (Zn)

Function of Zinc

Aids in cell division

In enzymes and auxins

• Zinc is mobile in plants.
• Mobility in soil decreases as pH increases.
• Availability is reduced by high pH, low levels of organic matter in mineral soils, soil compaction, excessive rates of P, and low temperature and wet soil.
• Organic matter can both inhibit and stimulate zinc uptake.
• Deficiency more common in sandy soils.

Nutrient deficiency symptoms - Zinc

• Spotting of older leaves, usually between veins
• Reddish brown spots on bean cotyledons
• Small, thin, yellow leaves
• Low yields
• Turf: small yellow leaves, stunted growth, thin shriveled, dark, desiccated-looking leaves starting with the youngest.

Nutrient excess symptoms - Zinc

None known

Sources

Zinc sulfate

 

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