Fertilizer

Fertilizers are natural or synthetic materials that are used to supply essential nutrients for PLANT growth. Plants require 16 nutrients for growth. Carbon (C), hydrogen (H) and oxygen (O) are taken up from the atmosphere and as water. The other 13 nutrients are taken up from the soil and normally divided into primary macronutrients nitrogen (N), phosphorus (P) and potassium (K), which are required in the largest amounts, the secondary macronutrients sulphur (S), calcium (Ca), and magnesium (Mg), needed in smaller amounts than the primary nutrients, and the micronutrients iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), chlorine (Cl) and molybdenum (Mo), which are required in very small amounts by the plant. In addition, nickel (Ni) has been shown to be necessary for legumes and cereal crops, and cobalt (Co) is also needed for some crops, including legumes where it is required for nitrogen fixation. When the elements that are essential for plant growth are not present in sufficient quantities or in the proper balance in agricultural systems, fertilizers can be applied to enhance plant growth and quality. As nutrients are removed from the soil when the crop is harvested, fertilizers are used to replenish the soil to sustain crop growth. The primary macronutrients are removed in the greatest amounts and so their addition in fertilizers is more commonly required than are the micronutrients, which are depleted much more slowly.

In North America, commercial macronutrient fertilizers are sold on the basis of the N, P2O5 and K2O content, expressed on a percentage basis. For example, 11-52-0 contains 11% N, 52% P2O5 and 0% K2O. If a fourth number is present, it refers to sulphur, as in ammonium sulphate, 21-0-0-24. Fertilizers in Canada are regulated under "The Fertilizers Act and Regulations," administered through the Canadian Food Inspection Agency, to ensure that the products are safe, efficacious and properly labelled.

Fertilizer can be inorganic (chemical) or organic. Manufactured inorganic fertilizers generally contain a high concentration of a few nutrients, with the concentration strictly controlled. Normally, the fertilizer is provided in a soluble form that is very quickly available for crop uptake. However, a number of enhanced efficiency fertilizers are available on the market; they use either physical coatings or chemical treatments to slow the release of nutrients into solution or delay their chemical transformation.

Organic fertilizers include naturally occurring materials such as barnyard manure, compost, or blood meal, and are normally much lower in nutrient content than are manufactured inorganic fertilizers. Therefore, a much larger volume of fertilizer must be applied to meet the nutrient requirements of crops, increasing the transportation costs. The composition of organic fertilizers is often variable, making it difficult to accurately assess application rates. However, organic fertilizers often contain organic matter that can contribute to both soil nutrient supply and physical properties. Whether the applied fertilizer form is organic or inorganic, plants absorb nutrients primarily in an inorganic ion form. Therefore, organic fertilizers must decompose to release these inorganic ions before the plant can use the nutrients. As a result, the release rate of nutrients from organic fertilizers is generally slower than from inorganic fertilizers. Since plants absorb nutrients in the inorganic form, food quality is not directly affected by whether the original source is organic or inorganic, although it can be influenced by the amount and balance of available nutrients.

While nutrient inputs are essential for crop productivity and to avoid soil nutrient depletion and degradation, environmental problems can occur with excess or poorly managed fertilizer inputs, whether from organic or inorganic sources. Emissions of reactive nitrogen to the atmosphere can harm ecosystem and human health, through acidification, CLIMATE CHANGE, eutrophication (nutrient enrichment), formation of ground-level ozone and particulate matter (microscopic particles that pollute the air), and loss of BIODIVERSITY. Carbon dioxide emissions from the large amount of fossil fuel used in fertilizer production and transport can also contribute to climate change. Movement of phosphorus fertilizer to water systems is a major cause of eutrophication, particularly in fresh-water systems, while the accumulation of trace elements such as cadmium (Cd) in the soil from phosphorus fertilization can lead to long-term soil degradation and reduce crop quality. Nutrient management practices that match nutrient supply to the crop demand more closely, both in terms of rate and timing of the applications, can improve nutrient use by crops and reduce potential environmental impacts. Enhanced efficiency fertilizers may also reduce the risk of nutrient loss. The selection of the correct nutrient source at an appropriate rate, timing and placement suited to the soil type, environment and production system is critical to optimise nutrient use efficiency and minimise nutrient loss.

CYNTHIA GRANT, TOM JENSEN

Fertilizer Industry

The fertilizer industry is one of the CHEMICAL INDUSTRIES. The major fertilizer types are potassium, urea and phosphate fertilizers; various sulphate compounds are also important. As each depends upon different chemical processes, each has a somewhat different history in Canada.

Nitrogen Fertilizers

Nitrogen fertilizers originally had to be derived from natural sources (eg, Chile's nitrate deposits). Large-scale synthetic nitrate production became possible after the 1908 discovery, by German chemists Fritz Haber and Carl Bosch, of a process for producing ammonia from atmospheric nitrogen and hydrogen. The process was applied to fertilizer production after the First World War. The ammonia, known as anhydrous (ie, water-free) ammonia, may itself be used as a fertilizer or may be used to produce other fertilizers. For example, ammonium nitrate is produced by combining anhydrous ammonia and nitric acid; urea is produced by combining anhydrous ammonia and carbon dioxide; ammonium phosphate is produced by combining anhydrous ammonia with phosphoric acid. In 1930, Cominco Ltd constructed an anhydrous ammonia plant at Trail, BC. Cominco Ltd became the world's first producer of granular fertilizers in 1932, of granular ammonium nitrate in 1963, and of granular urea in 1965. Presently there are numerous nitrogen producing plants in Canada, primarily in western Canada where natural gas is the energy source and one of the feed stocks to produce anhydrous ammonia initially, and further processed to produce other nitrogen fertilizers as noted above.

Phosphate Fertilizers

Phosphate fertilizers are made from phosphate rock (about 25% phosphorus), treated with sulphuric acid to produce phosphoric acid which, in turn, is used to manufacture fertilizers such as ammonium phosphate. Canada has some igneous phosphate rock deposits near Kapuskasing, Ont, that are mined and processed. It also imports crushed rock phosphate for processing, and significant amounts of finished ammonium phosphate and ammonium polyphosphate mainly from the US.

Potassium Fertilizers

Potassium fertilizer production in Canada began before the 19th century with the manufacture of POTASH from wood ashes. The industry expanded until the late 19th century, when Germany became the world's major potash supplier by mining potash (potassium chloride) deposits. Potash deposits were found in Saskatchewan in 1943 but development did not begin until 1954, when the Potash Corporation of America sank the first shaft at Patience Lake. There are presently numerous potash mines, mostly in Saskatchewan and to a lesser extent in New Brunswick. The Saskatchewan potash deposits are approximately 1000 m below the earth's surface in central Saskatchewan, and consist of a mineral deposit called sylvinite that contains both sodium chloride and potassium chloride. Most of the mines use a continuous conventional mining technique that uses rotating digging equipment connected to conveyor belt systems running many kilometres in tunnels. The ore is conveyed to a central shaft, where a large bucket elevator takes it to the surface for processing. The processing involves crushing of the ore, separation of the sodium and potassium chloride crystals, and granulation and sieving of the potash to the needed granulation size. The potash reserves in Saskatchewan and eastern Manitoba are considered some of the premium world reserves of potash and are estimated to contribute to world potassium production over the next number of centuries.

Sulphur Fertilizers

Sulphuric acid was first produced from metallic sulphides in 1866 and, in the 1920s, sulphuric acid production from base metal smelter gases began at Sudbury, Ontario, and Trail. The first sour-gas recovery plant in Canada was built in 1951, and there are now many plants in Alberta, BC and Saskatchewan that initially produce elemental sulphur. This byproduct of the oil and gas industry is used for many industrial processes. For fertilizers the main sulphur fertilizer is ammonium sulphate, manufactured by first burning elemental sulphur under contained conditions to make sulphur dioxide gas that is combined with water to form sulphuric acid. The sulphuric acid is then mixed with anhydrous ammonia to produce ammonium sulphate. There are also elemental sulphur fertilizers produced by grinding the elemental sulphur to a fine particle size and then combining it with bentonitic clay to produce a pastille the size of fertilizer granules that disperses upon wetting in soil. It takes time for the fine elemental sulphur particles to be oxidized by soil-inhabiting bacteria to produce the sulphate ions used by plants.

Micronutrient Fertilizers

Many of the other plant-necessary mineral nutrients are available as fertilizers and are applied to crops when portions of fields become depleted to the point that the specific nutrient is considered marginal or deficient in supply. The most common micronutrient fertilizers used are for supplying copper, zinc, boron and manganese. It seems that the longer crops are grown on soils the greater the chance there may be benefit from addition of other nutrients besides the more common nitrogen, phosphorus, potassium and sulphur fertilizers.