Nitrogen - Phosphorus - Potassium

Fertilizers are not plant food! Although it is common practice to call them food, this is a misnomer. Plants produce their own food using water, carbon dioxide and energy from the sun in the presence of chlorophyll in a process called photosynthesis.

Animals extract the energy trapped in the vegetative matter by eating it as food. Food implies a breaking down of complex matter into its component parts. Plants take the component parts and build them into complex organic matter. Nutrients in their environment comprise one of the vital component parts of photosynthesis. Fertilizers help provide these nutrients.
Plant nutrients consist of 17 elements essential to plant growth. Nitrogen, phosphorous and potassium are considered fertilizer macronutrients because plants require them in larger quantities for maximum growth. However, plants also need all of the other 14 elements in smaller amounts for proper growth. Fortunately, these minor elements are generally available in typical landscape soils.

Fertilizer Analysis

By law, all products that claimed to be nutrients for plant growth i.e. fertilizers, must be labeled with three numbers. These three numbers give the percentage by weight of nitrogen (N), phosphate (P205) and potash (K2O).
A fertilizer is said to be complete when it contains some percentage each of nitrogen (N), phosphorus (P) and potassium (K). Examples of commonly used complete fertilizers are 12-12-12, 26-16-16, 20-10-5.

An incomplete fertilizer will be missing one or two of the major components. Examples would be Urea 46-0-0, muriate of potash 0-0-60 or super phosphate 0-33-0.
Cottonseed meal, blood meal, bone meal, hoof and horn meal, fish emulsion and all manures are examples of organic fertilizers. Organic fertilizers usually contain relatively low concentrations of actual nutrients, but they perform other important functions which the synthetic formulations do not. These functions include: increasing organic content of the soil, improving physical structure of the soil and increasing bacterial and fungal activity.

Fertilizer Types

Although it is generally agreed that fertilizers come in three physical forms (liquid, solid and gas), there are actually only two classes of fertilizers: liquid and solid. Anhydrous ammonia (NH3) is a gas, but it is classified as a liquid because it is a liquid under pressure. The term liquid fertilizer applies to anhydrous ammonia, aqua ammonia, N solutions and liquid mixed fertilizers. Liquid N- P- K fertilizers are also known as fluid fertilizer. They include true solutions which require no agitation and suspensions or slurry type mixtures of N, P and K, which require constant stirring to keep the solids suspended in the solution.

Liquid or fluid fertilizer use has increased steadily over the last 3 decades, 9% of the total fertilizer sales consisted of liquids. Liquid fertilizers account for about 28% of the market.

Dry fertilizers (solids) still constitute the major part of the fertilizers sold. About 92% of the total dry fertilizer is sold as bulk material to farmers while only 8% in bags for the home consumer. Urea is the most popular source of dry N fertilizer, accounting for 79% of the total dry N sold. Ammonium sulfate has risen in popularity and constitutes around 14% of the dry N market.

Plant responses to liquid and dry fertilizer are similar, provided the same amounts of plant nutrients are applied and the same placement and water are similar. When placed in the soil, dry fertilizers absorb water and undergo chemical reactions similar to liquid fertilizer.

Characteristics and Uses

There are several properties of fertilizers and principles of fertilizer application which users should become familiar with. One important property of fertilizers is water solubility. Nearly all nitrogen fertilizers are completely water soluble. Because of their high water solubility, granule size and band placement are generally not important.

Effects of Over-Fertilizing

Fertilizers belong to the chemical category called salts. Salts have the characteristic of drawing moisture from their surroundings into the salt. When excessive amounts of fertilizers (or fresh manures) come into contact with plant roots, they will pull the moisture from the roots toward the salt. This collapses the plant cells and causes rapid dehydration of the plant tissue which is often called "burn".

Of course another impact of over-fertilization is that the excess nutrients may be leached or washed away and into a body of water such as a lake or stream. There, they may stimulate algae blooms causing a decrease in the water quality and having a negative impact on aquatic life.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

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