Inorganic fertilizers (Mineral Fertilizer)

Examples of naturally-occurring inorganic fertilizers include Chilean sodium nitrate, mined "rock phosphate" and limestone (a calcium source, but mostly used to reduce soil acidity).
Examples of manufactured or chemically-synthesized inorganic fertilizers include ammonium nitrate, potassium sulfate, and superphosphate, or triple superphosphate.

FERTILIZERS can be divided into macronutrients or micronutrients based on their concentations in plant dry matter. There are six macronutrients: nitrogen, potassium, and phosphorus, often termed 'primary macronutrients' because their availability is often managed with NPK fertilizers, and the 'secondary macronutrient', and calcium, magnesium, and sulfur, which are required in similar quantities but whose availability is often managed as part of liming and manuring practices rather than fertilizers. The macronutrients are consumed in larger quantities and normally present as whole number or tenths of percentages in plant tissues. There are many micronutrients, and their importance and occurrence differ somewhat from plant to plant. In general, most present from 5 to 100 parts per million (ppm) by mass. Examples of micronutrients are as follows: iron (Fe), manganese (Mn), boron (B), copper (Cu), molybdenum (Mo), and zinc (Zn).

Agricultural versus Horticultural Fertilizers

In general, agricultural fertilizers contain only one or two macronutrients. Agricultural fertilizers are intended to be applied infrequently and normally prior to or along side seeding. Examples of agricultural fertilizers are granular triple superphosphate, potassium chloride, urea, and anhydrous ammonia.Horticultural or specialty fertilizers, on the other hand, are formulated from many of the same compounds and some others to produce well-balanced fertilizers that also contain micronutrients. Some materials, such as ammonium nitrate, are used minimally in large scale production farming. The 18-51-20 example above is a horticultural fertilizer formulated with high phosphorus to promote bloom development in ornamental flowers. Horticultural fertilizers may be water-soluble (instant release) or relatively insoluble (controlled release). Controlled release fertilizers are also referred to as sustained release or timed release. Many controlled release fertilizers are intended to be applied approximately every 3-6 months, depending on watering, growth rates, and other conditions, whereas water-soluble fertilizers must be applied at least every 1-2 weeks and can be applied as often as every watering if sufficiently dilute. Unlike agricultural fertilizers, horticultural fertilizers are marketed directly to consumers and become part of retail product distribution lines.

Organic fertilizers

Examples of naturally occurring organic fertilizers include manure, slurry, worm castings, peat, seaweed and guano. Green manure crops are also grown to add nutrients to the soil. Naturally occurring minerals such as mine rock phosphate, sulfate of potash and limestone are also considered Organic Fertilizers. Examples of manufactured organic fertilizers include compost, bloodmeal, bone meal and seaweed extracts. Other examples are natural enzyme digested proteins, fish meal, and feather meal. The decomposing crop residue from prior years is another source of fertility.

Organic fertilizers help in mobilizing existing soil nutrients, so that good growth is achieved with lower nutrient densities while wasting less, releasing nutrients at a slower, more consistent rate, helping to avoid a boom-and-bust pattern
Helping to retain soil moisture, reducing the stress due to temporary moisture stress, improving the soil structure
Organics also have the advantage of avoiding certain long-term problems associated with the regular heavy use of artificial fertilizers.

Environmental effects of fertilizer use

Over-application of chemical fertilizers, or application of chemical fertilizers at a time when the ground is waterlogged or the crop is not able to use the chemicals, can lead to surface runoff (particularly phosphorus) or leaching into groundwater (particularly nitrates). One of the adverse effects of excess fertilizer in lacustrine systems are algal blooms, which can lead to excessive mortality rates for fish and other aquatic organisms. When prolonged algae blooms occur over many years, the effect is a process called eutrophication. Excessive nitrogen fertilizer applications can lead to pest problems by increasing the birth rate, longevity and overall fitness of certain pests. It is also possible to over-apply organic fertilizers. However: their nutrient content, their solubility, and their release rates are typically much lower than chemical fertilizers, partially because by their nature, most organic fertilizers also provide increased physical and biological storage mechanisms to soils.

The problem of over-fertilization is primarily associated with the use of artificial fertilizers, because of the massive quantities applied and the destructive nature of chemical fertilizers on soil nutrient holding structures. The high solubilities of chemical fertilizers also exacerbate their tendency to degrade ecosystems.

Storage and application of some fertilizers in some weather or soil conditions can cause emissions of the greenhouse gas nitrous oxide (N2O). Ammonia gas (NH3) may be emitted following application of inorganic fertilizers, or manure or slurry. Besides supplying nitrogen, ammonia can also increase soil acidity (lower pH, or "souring").The concentration of up to 100 mg/kg of Cadmium in phosphate minerals increases the contamination of soil with Cadmium. Uranium is another example for impurities of fertilizer