Fertilizer Terms and Labeling
To get the most value out of your lawn fertilizer, an understanding of what your lawn needs and what a particular fertilizer can supply is essential. If you understand what is on the label you can make the right selection, save money and help protect the environment.
There are literally hundreds of fertilizer formulations available, each with a different analysis, which means they contain different amounts of nutrients. Nutrients contained in a fertilizer are indicated on the label by the large numbers on the bag. A complete fertilizer is one that contains nitrogen (N), phosphorus (P), and potassium (K).
Ever wonder why the letter K stands for potassium? The letter K stands for kalium which was taken from the word "alkali". Alkali is from the Arabic word al qaliy which means "the calcined ashes'.1 Calcined ashes are the result of heating a substance to a high temperature causing a loss of moisture2.
Historically, wood and other vegetable matter was obtained by burning it, soaking the ashes in water, and evaporating the resulting liquid in iron pots to obtain the salts. These salts were largely used in the manufacture of soap. The salts were called in early modern Dutch potasschen, literally 'pot ashes', and the word was adopted into English as potash. The term potassium was given for the metallic element which occurs in potash by the chemist Sir Humphry Davy in 18073.
In early colonial days in the United States, potassium from wood ashes was one of the first important chemical enterprises. A patent for the preparation of potassium salts was granted in 1790. Potash is the trade term commonly used for potassium-containing fertilizers in the turfgrass industry4.
For a more complete discussion of this element and its role as a plant nutrient click here.
- Wikipedia Online Dictionary. Kalium. Online. Wikimedia Foundation, Inc.; c2003 [modified 2010 Aug 18; cited 2010 Aug 18]. Available from: http://en.wikipedia.org/.
- The Free Dictionary. Calcined. Online. Huntingdon Valley (PA): Farlex, Inc.; c2010 [cited 2010 Aug 18]. Available from: http://www.thefreedictionary.com/.
- Word Origins World History. Potash. Online. WebFinance, Inc.; c2010 [cited 2010 Aug 5].
- Tisdale SL, Nelson WL, and Beaton JD. 1985. Soil Fertility and Fertilizers, 4th Ed., Macmillan, New York, N.Y. p. 433.
A balanced fertilizer contains equal parts N, P and K. A fertilizer that contains 10-10-10 is a complete, balanced fertilizer. A fertilizer that contains 25-5-15 is complete but not balanced. A fertilizer that contains 25-0-15 is incomplete and not balanced.
Depending on your soil nutrient status you may not need all the nutrients in a complete fertilizer. The only way to know is to have your soil tested. Contact University of Minnesota Soil Testing Lab or your local county extension office for more information on soil testing or to have a soil test kit sent to you. Table 7.1 explains the information on a fertilizer label that is required by law.
Table 7.1. Information on a Fertilizer Label that is Required by Law:
- Net weight of the fertilizer in the container.
- Name brand or trademark.
- Guaranteed chemical analysis which may include percent water insoluble nitrogen.
- Manufacturer's name and address.
- Directions for use.
- Nutrient sources.
More detail pertaining to the Minnesota Fertilizer Labeling Law can be found in Chapter 18C.215 of Minnesota Statues.
Two very important features on the label are the guaranteed analysis and the net weight. The guaranteed analysis is a minimum analysis. That is, the percentage of nutrients in the container has to be present in at least that quantity. For example, a fertilizer product stating that it contains 5 percent N could contain 7 percent N without violating the law. However, if it only contained 4 percent N it would be a violation of the fertilizer labeling law. The guaranteed analysis is always given in a specific order and is given as the percent of nitrogen for the first number, the percent of phosphate for the second number, and percent potash for the third number.
In the fertilizer example described in Table 7.2, there is 30 percent nitrogen, 4 percent phosphate and 4 percent potash. Nitrogen is the first number, phosphate (P2O5), is the second number, and potash (K2O) is the third number.
Only nitrogen is given as the actual percentage of the nutrient. The actual amount of phosphorus (phosphate) and potassium (potash) are given as percents of their oxide forms (i.e., the element is combined with oxygen). This is not a problem because soil tests are usually reported in these same oxide forms as are the recommendations for fertilizer application.
Table 7.2. Hypothetical Example of Information Presented on a Lawn Fertilizer Bag
EASY GREEN LAWN FERTILIZER
30-4-4 (guaranteed analysis):
Total Nitrogen (N)....................30%
- 12.5% Ammoniacal Nitrogen
- 10% Urea
- 7.5% Water Insoluble Nitrogen* (WIN)
Available Phosphate (P2 O5 ) .......4%
Available Potash (K2 O) ...............4%
Derived from: Urea, *Methylene Ureas, Ammonium Phosphate, Ammonium Sulphate, Muriate of Potash.
Easy Green Corporation
Greenlawn, MN 54321
Net Weight 60 lbs.
Proceed to Getting What You Paid For.