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What Is NPK Fertilizer

Photo of npk fertilizer The big three, N.P.K. - organic fertilizers
contain many other nutrients

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NPK Fertilizer

There are thirteen known mineral elements which plants absorb through their leaf and root systems providing all the nutrients needed for health and growth.

The mineral nutrients are divided into two groups:

  • macro nutrients
  • micro nutrients.

Macro nutrients are broken into two more groups according to how much plants need of each:

  • Major or Primary Nutrients
  • Minor or Secondary Nutrients.

The three major nutrients that most people are familiar with are nitrogen (N), phosphorus (P) and potassium (K). The standard labeling always lists these three essential nutrients in this order because they are recognizes as the three main contributors to plant nutrition for growing green leaves, making seed and fruit, and growing cells.

Minor or Secondary NPK Fertilizer Nutrients

These are calcium (Ca), magnesium (Mg), and sulfur (S). The amount of calcium and magnesium present usually depends on the amount and type of lime present or added to the soil. Sulfur is usually found in sufficient quantities in soils containing good amounts of organic matter.

Micro nutrients

Along with the macro nutrients there are a number of micro nutrients that plants need, either directly or indirectly, for healthy growth. These elements, sometimes called trace elements, are only needed in very small quantities, they are boron (B), copper (Cu), iron (Fe), chloride (Cl), manganese (Mn), molybdenum (Mo) and zinc (Zn).

Recycling organic matter such as grass clippings and leaves into compost or mulch is an excellent way of providing all the micro nutrients that are necessary to growing plants.

The Big Three

Short version

  • N - Nitrogen is responsible for producing leaf growth and is the main chemical involved in photosynthesis.

  • P - Phosphorus (Phosphate) aids in plant maturity, supports the vigorous development of roots, stems, blossoms, and fruits.

  • K - Potassium (Potash) strengthens the overall plant, providing resistance to disease and reduces plant stress. Aids in early growth, stem strength and improves the color and flavor of fruit.

Plant Growth And Deficiency Problems

Nitrogen (N)

Nitrogen is necessary for aboveground growth of plants, it is considered one of the most important plant nutrients. Nitrogen is used to make proteins that build cell material and plant tissue, promoting growth of the stems and leaves which is especially important for leaf crops such as cabbage, lettuce and spinach. In addition, it is necessary for the function of other essential biochemical agents. Including photosynthesis, enzymes that help plants assimilate nutrients and nucleic acids which are involved in the healthy development of fruit flowers and seeds. Of all the major plant nutrients, Nitrogen is often the most important deciding factor in plant growth and crop yield.

Excess nitrogen can also cause problems by producing excessive vegetation in certain crops where excessive leaf development is detrimental to the crop in reducing the quality of the root, fruit or flower.

The best organic sources of nitrogen come from

Deficiency Symptoms:

Nitrogen deficiency causes stunted or slow growth, slender fibrous stems and the classic yellowing of the leaves. Younger leaves remain green longer, because they receive soluble forms of nitrogen transported from the older leaves. This usually causes the yellowing, and in server cases dropping, of the leaves to start farthest from the growing shoots.

Phosphorous (P)

The phosphorus content of a fertilizer is calculated in percent of the phosphate present.

Phosphorus helps plants transport and assimilate nutrients, it is a major building block in all living plants. It is responsible for the storage of energy. The energy stored allows for the transportation of nutrients across the cell walls of the plant. Good plant phosphorus levels ensure that crops will reach their full potential for healthy development of fruit flowers and seeds. Phosphorus helps to build plant vitality and is of special importance in the processes concerned in the development of the strong root systems that ensures better resistant to root rot diseases.

The best organic sources of phosphate come from

Deficiency Symptoms:

Phosphorous deficient plants are usually dwarfed and spindly. The leaves, in contrast to those lacking nitrogen, are often dark green with purple tints. Under side of the leaves are reddish or purple. Leaf veins and margins often turn bronze. Deficiency symptoms occur first in more mature leaves. Fruit development is usually delayed.

Potassium (K)

The potassium content of a fertilizer is calculated in percentage of the potash present.

Potassium enables plants to develop strong, thick stems, healthy roots and large, plentiful fruit. Plants require larger quantities of potassium than any other nutrient. Potassium is associated with movement and retention of water, nutrients, and carbohydrates in plant tissue. Stimulates early growth and hastens maturity. Potassium is a key nutrient in the plants tolerance to stresses such as cold-hot temperatures, improves resistance to pests and diseases and is essential for the development of fruits flowers and seeds.

The best organic sources of potassium are

Deficiency Symptoms:

As with nitrogen and phosphorus, potassium is easily redistributed from mature leaves to the younger ones. Therefore deficiency symptoms will appear first in the older leaves. These become ash-grey colored instead of deep green, will look scorched at the edges (marginal chlorosis) and start to crinkle or curl with mottled yellow tips that later turn bronze.

Plants deficient in potassium often develop weak stem and stalks, Small fruit and shriveled seeds along with poor growth and yields, they become susceptible to disease.

Minor or Secondary Nutrients

Calcium (Ca)

Calcium is a major building block for plant tissues, neutralizing certain acids formed in plants and helps in the manufacture of protein. In fact it should be the big 4 (N.P.K.C.) not the big 3 (N.P.K.). Calcium activates enzymes, is a structural component of cell walls, influences water movement in cells and is necessary for cell growth and division. It is largely responsible for the availability of nutrients to plants and has a strong influence on microbial activity.

Deficiency Symptoms:

These include black spots on the leaves and potential fruits and stunted plants. Blossom end rot in tomatoes, where the tips of the fruit blacken and rot, is a classic case. Tip burn on lettuce and black heart in celery are also a result of calcium deficiency.

Sulfur (S)


Sulfur is a structural component of amino acids, enzymes, proteins and vitamins and essential for protein synthesis, chlorophyll transport and nitrogen utilization. Sulfur improves root strength and growth of plants as well as having an influence on improving the flavor and taste in many vegetables. Although sulfur is classed as a trace element it is needed in fairly large quantities. Sulfur is readily lost by leaching from soil and should be applied with a nutrient formula.

Deficiency Symptoms:

Include slow growth rate and delayed maturity, young leaves light green to yellowish color, small and spindly plants. These problems will be rare on soils that have good organic content and supplied with ample manure.

Magnesium (Mg)

Magnesium is another element required in larger quantities than most people realize. It should be in similar quantities as phosphorus. Magnesium plays an important part in photosynthesis, is necessary for functioning and activation of plant enzymes to product carbohydrates, sugars, proteins and fats. It is also vital in the production of healthy and correctly structured fruits and flowers and seeds and in fact magnesium is essential to all the metabolic pathways in plants.

Deficiency Symptoms:

Deficiency is marked with whitish stripes between the leaf veins and yellowing of the leaves, beginning, as with other nutrient deficiencies in the older leaves.

Organic Plant Nutrients

Common Sources Of Organic Plant Nutrients
Nitrogen Phosphorus Potassium
Blood mealsRock PhosphateManure
Hoof and horn meal Guano-High PGreensand
Fish mealColloidal phosphatePotash Salts
Guano-High NBone MealSeaweed-Kelp
Seed mealsWood Ash

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More Information

NPK Fertilizer

Marginal chlorosis is the yellowing of leaf margins.

NPK Fertilizer

plant and animal by-products such as alfalfa, blood meal, bone meal, fish, feather meal, manure and soybean meal.

NPK Fertilizer

rock phosphate, colloidal phosphate (soft rock phosphate), bone meal, bat guano.

NPK Fertilizer

compost, manure, kelp, greensand, potash salts and hardwood ash.

NPK Fertilizer

Sulfate is the water-soluble and readily available form of sulfur

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