What's In The Bag?
Spring is here, and you can't help but notice that the stores are loading up with bags of fertilizer. Why do we apply lawn and garden fertilizer every year? What is in that bag anyway, and where does it come from?
What do those three numbers mean?
The label on a package of manufactured fertilizer shows the amount of nitrogen, phosphate and potassium present in that formulation. For example, a bag marked 7-7-7 contains 7 per cent nitrogen, 7 per cent phosphate and 7 per cent potassium.
Nitrogen
The first number that you see on the bag shows the nitrogen content. The air we breathe contains about 75% nitrogen. Incredibly, the large volume of atmospheric nitrogen represents only about 2% of the total nitrogen found on the planet. Most of the nitrogen is found in plants, rocks, and coal. Nitrogen is not manufactured; in a process that imitates nature, it is simply borrowed from the air and transformed into forms that can be applied and used by plants. Nitrogen fertilizers are produced by taking nitrogen and carbon dioxide gas from the air and combining them with hydrogen from natural gas to form a nitrogen fertilizer such as ammonia or urea. Urea is the most common form of nitrogen found in a bag of lawn fertilizer. If you left a urea granule out in the sun for a few hours, it would simply vaporize into ammonia and carbon dioxide gas. Nitrogen's main benefit is to support rapid and healthy plant growth.
Phosphate
The second number on the fertilizer bag represents its phosphate content. Phosphate is widely distributed in soil, minerals, water and all living tissue. Like nitrogen and potash, phosphate is an essential element for both plant and animal life. It is especially important to germinating and young plants, because it greatly helps in the establishment of a strong root system.
Of the known elements, phosphate ranks eleventh among the most abundant elements in the earth's crust. One of the earliest phosphate mines in North America was located right here in Ontario near Brockville. Bones, phosphate rock, and organic matter are important sources of this mineral. In 1842, John Bennett Lawes, an English country squire, discovered that the phosphate in bones would be more available to plants if the bones were treated with acid. The same process was also successful on phosphate rock. Lawes patented his process and called his new fertilizer 'super phosphate.' Refined versions of Lawes' process are still used to produce phosphate fertilizers today. The North American supply of phosphate now largely comes from sites in Florida. Since phosphate is important during the early stages of plant development, fertilizer with a high ratio of phosphate such as 10-52-10 and 10-25-10 is helpful when starting new plants.
Potassium
The potassium content is the third number shown in the ratio on a fertilizer bag. The source of fertilizer potassium is potash. That term originates from the early method of leaching wood ashes and then evaporating the solution in iron pots to obtain 'pot-ash'. This product was used to make soap, glass, and cloth, among other things. In the tenth century, the Chinese developed gunpowder using charcoal, sulfur and saltpeter (a salt of potash called potassium nitrate). Saltpeter was used in curing meats such as ham.
Potash is abundant in nature, comprising 2.4% of the earth's crust. All naturally occurring potash in the soil originated from the decomposition of feldspars and micas. Much of the world's reserve of potash comes from what is believed to be evaporated sea beds in Saskatchewan and New Mexico. Potash is also extracted from the Dead Sea in the Middle East and The Great Salt Lake in Utah.
Potash is essential for plant hardiness as well as tolerance to drought, cold and heat. It also makes the grass on our lawns and parks more tolerant to heavy foot traffic and safer cushioning surfaces for sports activities.
Where does fertilizer come from? The granules inside a bag of fertilizer are borrowed from the air and earth -- and will eventually be recycled back to the air or earth by plants and microorganisms in the soil.
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