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NPK Fertilizers: Definition & Uses

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  • 0:04 Fertilizer Facts
  • 0:41 NPK Fertilizers
  • 1:44 How Nitrogen Is Obtained
  • 2:29 How Phosphorous Is Obtained
  • 3:22 How Potassium Is Obtained
  • 3:47 Lesson Summary
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Lesson Transcript
Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

Fertilizers probably don't sound exciting, but they actually are! This lesson will explore what NPK means, as well as how the elements are obtained for this type of fertilizer.

Fertilizer Facts

Did you know that in some parts of the world, people use their own feces as fertilizer? A fertilizer is just something that is added to the soil to increase plant productivity. Check out these other fun fertilizer facts:

  • There's evidence to suggest that the bones of soldiers who were killed in the Battle of Waterloo were pulverized and used as a fertilizer by farmers (phosphorus, an important part of fertilizer, is found in bones)

  • China consumes the most fertilizer in the world

  • In the United States the three crops that use the most fertilizers are soybean, corn, and wheat

  • 33,000 jobs exist in the United States just from making fertilizer

NPK Fertilizers

There are fertilizers that are natural, like manure, and fertilizers that are man-made. NPK fertilizers are fertilizers that contain the elements nitrogen (N), phosphorus (P), and potassium (K).

Why these elements? Well, each element has been found to improve the health and appearance of plants. For example,

  • Nitrogen is good at making the leaves grow

  • Phosphorus improves fruit and/or flower production as well as root growth

  • Potassium is great for overall plant health

Often the soil the plants are growing in lacks some of these nutrients, so by adding them in as a fertilizer, plants do better. Let's say you buy a 50 lb. bag of fertilizer that says 10-6-4 on it. The first number represents nitrogen, the second number is phosphorus, and the third is the potassium. And, if it is a 50 lb. bag, the numbers indicate that 5 lbs. is nitrogen (or 10%), 3 pounds is phosphorus (or 6%), and 2 pounds is potassium (or 4%).

Now that you know what NPK fertilizer is, let's check out how it's made.

How Nitrogen Is Obtained

So, how is nitrogen obtained? Nitrogen makes up a large percentage of the atmosphere (about 78%), and someone discovered a way to take nitrogen from the air. More specifically, nitrogen in the air is reacted with hydrogen to form ammonia, and from there other nitrogen-containing substances can be made.

For example, reactions with ammonia result in ammonium salts, ammonium nitrate, and nitric acid. All of these can be added to fertilizer to increase the amount of nitrogen. So if you check out the ingredients on a fertilizer bag, you may see nitrogen broken down into types of nitrogen. You may have never realized the importance of nitrogen fertilizer in your life, but it's estimated that nearly half of all of the food produced in the world is grown with the help of a nitrogen fertilizer!

How Phosphorus Is Obtained

The next ingredient in NPK fertilizer is phosphorus, which is obtained from mining phosphate rock (sounds much better than from the bones of people, doesn't it?). The phosphate rock can be exposed to different acids to make the ingredients required for fertilizer. Let's take a moment to go over some of the reactions between phosphate rock and acids.

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