The use of fertilizer has become increasingly indispensable in food and fiber production and the maintenance of horticultural plantings. Manufactured fertilizers have been used for 100 years. Because of the introduction of fertilizer in developing countries, there is considerably more hope that the world's increasing population (6 billion) may some day be adequately fed. Yet, there is some evidence that excessive fertilizer use may be hazardous to human health and the environment.
See Links Information on Hypoxia in the Gulf of Mexico & Eutrophication for more information.
The justification for future fertilizer use must be based on an understanding of the benefits of proper use, as well as on an understanding of the ill effects that can result from improper use. Using fertilizers is not a simple procedure, and understanding the terminology is an important first step in their proper use.
All
commercial fertilizers must display a printed tag which identifies the name
brand, trademark material, producer, chemical analysis of every constituent
claimed to be present and the materials from which all constituents were
derived.
The numbers on a bag of fertilizer--"15-25-10", for example--are the guaranteed chemical analysis. These numbers indicate the bag of fertilizer contains: 15% N, 25% P2O5, and 10% K2O. These numbers--"15-25-10"--are referred to as the fertilizer grade.
Notice that, for phosphorus and potassium, the chemical analysis is given in
the oxide form. This is the way the nutrients were first thought to be absorbed
by the plant and is still used today to express the analysis of fertilizer. The
elemental analysis for this fertilizer is
15 - 11 - 8.3 The elemental analysis can
usually be found on the bag near the fertilizer grade.
To convert from the elemental analysis to the chemical analysis for
phosphorous and potassium fertilizers, use this formula:
%P x 2.29=%P2O5 (and %
P2O5 ÷ 2.29=%P); use %K x 1.2=%K2O (and
%K2O ÷1.2=%K.)
For Example: A 30 pound sack of fertilizer (25 - 5 - 5) , is applied to your garden.
The amount of N applied=.25 x 30=7.5 lbs N
amount of P 205 applied=.05 x 30=1.5 lbs &
P=.44 x 1.5=0.66 lbs P
amount of K20 applied=.05 x 30=1.5 lbs & K=.83 x
1.5=1.245 lbs.K
Chapter 2 Fertilizer Problems
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