Forms and Function of Essential Plant Nutrients - Valley Crops Home
Forms and Function of Essential Plant Nutrients - Valley Crops Home
Forms and Function of Essential Plant Nutrients - Valley Crops Home
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<strong>Forms</strong> <strong>and</strong> <strong>Function</strong>s <strong>of</strong> <strong>Essential</strong> <strong>Plant</strong> <strong>Nutrients</strong><br />
Brian Jones, Extension Agent Augusta County<br />
There are 16 elements required by plants. Three <strong>of</strong> these: carbon (C),<br />
oxygen (O 2 ) <strong>and</strong> hydrogen (H) are taken from either atmospheric carbon dioxide<br />
or water. The other 13 nutrients are taken up by plants from the soil or by foliar<br />
applications. Of these 13, three are called primary nutrients: nitrogen (N),<br />
phosphorus (P) <strong>and</strong> potassium (K), three are secondary: calcium (Ca),<br />
magnesium (Mg) <strong>and</strong> sulfur (S) <strong>and</strong> seven are micronutrients: boron (B), chlorine<br />
(Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) <strong>and</strong> zinc (Zn).<br />
Primary nutrients are commonly supplied to the plant either as blended<br />
fertilizers or as organic forms (manure or poultry litter). These nutrients are<br />
utilized in the largest amounts by crops, <strong>and</strong> thus are typically applied at higher<br />
rates than secondary nutrients <strong>and</strong> micronutrients. Secondary nutrients are still<br />
required by the plant, but in smaller amounts than primary nutrients. These<br />
nutrients are available in many forms, such as fertilizers or manures, but may<br />
also be available through applications <strong>of</strong> lime or gypsum. Micronutrients are<br />
required in even smaller amounts than secondary nutrients <strong>and</strong> are available in<br />
various forms depending on the application.<br />
The following paragraphs will discuss the function <strong>and</strong> forms <strong>of</strong> the three<br />
primary nutrients, <strong>and</strong> will also touch on basic deficiency symptoms in the plant.<br />
Nitrogen<br />
<strong>Function</strong><br />
Of the three primary nutrients, plants require nitrogen in the largest amounts.<br />
<strong>Plant</strong>s typically contain between 1 <strong>and</strong> 5% N by weight. It is absorbed by plants<br />
as either nitrate (NO 3 - ), ammonium (NH 4 + ) or urea. Once taken up by the plant,<br />
the NO 3 - form must be reduced to either NH 4 + or ammonia (NH 3 ). The NH 3 is<br />
then used to create numerous amino acids that are incorporated into proteins<br />
<strong>and</strong> nucleic acids (DNA, RNA). These proteins become the framework for<br />
chloroplasts, mitochondria <strong>and</strong> other structures in which most biochemical<br />
reactions occur. Nitrogen is also an integral part <strong>of</strong> chlorophyll, the primary<br />
absorber <strong>of</strong> light energy needed for photosynthesis. Photosynthesis is the<br />
process through which plants use light energy to convert carbon dioxide into<br />
carbohydrates (sugars) which provide energy required for plant growth <strong>and</strong><br />
development.<br />
Nitrogen:<br />
1. Promotes vigorous vegetative growth<br />
2. increases leaf size <strong>and</strong> quality<br />
3. hastens crop maturity<br />
4. promotes fruit <strong>and</strong> seed development<br />
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<strong>Forms</strong><br />
Nitrogen fertilizer is available to the plant from several different sources, including<br />
fertilizers, manures <strong>and</strong> legumes. The amount <strong>of</strong> nitrogen from organic forms<br />
varies depending on the origin, how it was h<strong>and</strong>led <strong>and</strong> stored <strong>and</strong> the<br />
decomposition rate <strong>of</strong> the material. Common inorganic fertilizer forms <strong>of</strong> N<br />
available in Virginia include:<br />
- Ammonium nitrate (33-0-0)<br />
- Ammonium sulfate (21-0-0-24S)<br />
- Diammonium phosphate or DAP (18-46-0)<br />
- Urea (46-0-0)<br />
- Urea ammonium nitrate or UAN (liquid form containing 30% N by<br />
weight)<br />
Nitrogen Deficiency<br />
<strong>Plant</strong>s that are deficient in N typically show stunted growth <strong>and</strong> their foliage is<br />
pale green. Symptoms generally appear on the bottom leaves first, <strong>and</strong> lower<br />
leaves will sometimes have a “fired” appearance on the tips, turn brown <strong>and</strong> fall<br />
<strong>of</strong>f. In crops such as vegetables, forage <strong>and</strong> pasture, low N results in low yield<br />
<strong>and</strong> quality. With grain crops, such as corn <strong>and</strong> small grains, deficiency results in<br />
yellow leaf tips, stunted growth with spindly stalks <strong>and</strong> low yields <strong>of</strong> poor quality<br />
grain. Too much N causes excessive vegetative growth, delays maturity,<br />
increases lodging risk <strong>and</strong> promotes plant diseases.<br />
Phosphorus<br />
<strong>Function</strong><br />
<strong>Plant</strong> growth will not occur without phosphorus (P). Concentration <strong>of</strong> P in most<br />
plants is between 0.1 <strong>and</strong> 0.4%, lower than either N or potassium. <strong>Plant</strong>s absorb<br />
P either as H 2 PO 4 - or HPO 4 2- orthophosphate ions, depending on the pH. <strong>Plant</strong>s<br />
may also absorb organic phosphate forms, made available as soil organic matter<br />
is decomposed. The most essential function <strong>of</strong> P in plants is in energy storage<br />
<strong>and</strong> transfer. Nucleic acids, phospholipids, coenzymes DNA <strong>and</strong> NADP, <strong>and</strong><br />
most importantly ATP rely on P for the energy required to function. ATP is the<br />
source <strong>of</strong> energy that powers practically every energy-requiring biological<br />
process in plants. Phosphorus is also required for other essential metabolic<br />
processes, such as photosynthesis, glycolysis, respiration, <strong>and</strong> fatty acid<br />
synthesis.<br />
Phosphorus:<br />
1. Enhances seed germination <strong>and</strong> early growth<br />
2. Is associated with increased root growth<br />
3. Stimulates blooming <strong>and</strong> bud set<br />
4. Improves straw strength<br />
5. Increases disease resistance<br />
6. Aids in seed formation<br />
7. Hastens plant maturity<br />
8. Provides winter hardiness<br />
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<strong>Forms</strong><br />
Phosphorus is made available to the plant through fertilizer or organic forms.<br />
Some common forms <strong>of</strong> P fertilizer in Virginia include:<br />
- Monoammonium phosphate, or MAP (11-48-0)<br />
- Diammonium phosphate, or DAP (18-46-0)<br />
- Triple super phosphate (0-46-0)<br />
- Various liquid forms, including 10-34-0 or 9-18-9<br />
Phosphorus Deficiency<br />
<strong>Plant</strong>s deficient in P typically have stunted growth. Leaves in some cases may be<br />
dark green with a leathery texture, with reddish purple leaf tips <strong>and</strong> margins. In<br />
corn, reddish purple leaf margins are characteristic <strong>of</strong> P deficiency. Deficiency<br />
symptoms may appear even when soil P levels are adequate, particularly if soil<br />
temperatures are less than 60°F. When soil is cool, less P is made available for<br />
plant uptake. These symptoms will generally disappear as soils warm.<br />
Potassium<br />
<strong>Function</strong><br />
Potassium has many functions in plant growth, but primarily acts as a regulator<br />
for the many metabolic processes required for growth, fruit <strong>and</strong> seed<br />
development. Potassium (K) is actively taken up from the soil solution by plant<br />
roots. Potassium concentrations in most plants range from 1 to 4% by weight.<br />
<strong>Plant</strong>s require a good deal <strong>of</strong> K to properly function. Unlike the other primary<br />
nutrients, K forms no other compounds in the plant, but remains a lone ion.<br />
Potassium is also vital for animal <strong>and</strong> human nutrition, <strong>and</strong> thus healthy fruits,<br />
vegetables <strong>and</strong> grains must have adequate levels <strong>of</strong> K.<br />
Potassium:<br />
1. Adds stalk <strong>and</strong> stem stiffness<br />
2. Increases disease resistance<br />
3. Increases drought tolerance<br />
4. Gives plumpness to grain <strong>and</strong> seed (increasing<br />
kernel <strong>and</strong> test weight)<br />
5. Improves firmness, texture, size <strong>and</strong> color <strong>of</strong> fruit<br />
crops<br />
6. Increases oil content <strong>of</strong> oil crops<br />
7. Regulates opening <strong>and</strong> closing <strong>of</strong> cell stomata,<br />
increasing water use efficiency<br />
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<strong>Forms</strong><br />
Potassium can be made available to crop plants either as commercial inorganic<br />
fertilizers or through manure. Only a few inorganic forms <strong>of</strong> potash are typically<br />
available in Virginia, including:<br />
- Potassium chloride, or muriate <strong>of</strong> potash (0-0-60)<br />
- Potassium sulfate (0-0-50-16S)<br />
- Potassium magnesium sulfate (0-0-22-23S-11Mg)<br />
Potassium Deficiency<br />
<strong>Plant</strong>s deficient in K generally exhibit chlorosis (a loss <strong>of</strong> green color) along the<br />
leaf margins or tips starting with the bottom leaves <strong>and</strong> moving up the plant. In<br />
severe cases, whole plant yellowing may occur <strong>and</strong> the lower leaves may fall <strong>of</strong>f.<br />
Grain crops will have weak stalks, small grain size <strong>and</strong> low yields. Forage crop<br />
yield, vigor <strong>and</strong> quality will be low. Often however serious K deficiencies can<br />
occur without the appearance <strong>of</strong> deficiency symptoms.<br />
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