Plant nutrients explained by Mr. Cosby

    Do you remember what atoms and molecules are?  Do you remember that all matter on Earth is made out of atoms, including living things like you and plants?  Do you remember the periodic table of elements?  The Periodic Table is just a list of all of the known "types" of atoms.  So, you, plants, and all of the non-living things on Earth are made out of atoms from the periodic table.  So if you could look really closely at a plants cells, exactly which elements from the periodic table is the plant made out of??  You might be surprised to learn that approximately 94% of a plant's mass comes from the three big elements that a plant takes in during photosynthesis; carbon from carbon dioxide, hydrogen and oxygen from water.  Yes, this means 94% of the matter in a plant is just Carbon, Hydrogen, and Oxygen!!!  This leaves the other 6% of a plant's mass to a variety of other elements we will refer to simply as "plant nutrients".  These nutrients 
are the elements or compounds required by
organisms in
small amounts to help their cells carry out the processes of life.   The most common elemental nutrients taken in by plants are nitrogen, phosphorus, sulfur, calcium, iron, and magnesium.  While these nutrients are sparingly used, they are still vital to the survival of producers.  For example, without nitrogen, plants would not be able to make the protein structures their cells need to build organelles, and so plant cells would not exist at all!  Phosphorus is needed by cells to make cell membranes and DNA.  A lack of either of these nutrients hurts plant growth, and with a large enough deficiency death is likely for the plant!  These elements are naturally found in rocks, soil, or decaying matter and are soluble in water making them readily available for plants to take advantage of when they absorb nutrient-rich water through their roots!   

    In regions where soil is missing some of these nutrients, farmers often put fertilizer on their crops.   Fertilizers are typically made from animal or plant waste (dead organisms), chemicals, human or animal sewage, or peat (a not-completely-decayed form of coal) and have very high concentrations of these elements.  Unfortunately, measuring the needs of plants is difficult.  In a single field, some of the soil may be rich in nutrients while other areas are completely bare.  The
quick solution for farmers is to simply over-fertilize a field, and not worry about what happens to the extra nutrients.  The excess nutrients that are not absorbed by plants wash into streams and rivers.  These nutrients also find their way into waterways in pollution from factories, and even through household products.  For instance, your shampoo likely contains phosphorus and nitrogen compounds.   Every flush of the toilet carries "nutrients" in the form of your human waste into the sewer.  When you mow the lawn and bag the dead grass, you are essentially putting a 30 pound bag of decaying nutrients into the landfill.  Where do all of these nutrients go?  What happens to them when you rinse the shampoo out of your hair?  Where does that pipe on your toilet lead to?  Does the grass stay in the landfill forever?  Do unused nutrients simply disappear?  Or.. do producer organisms somewhere use them??"

Check out the pictures below to see the affect of nutrient "over-use" in an ecosystem!

For more on Micronutrients:

This is a picture of a river, just downstream from a farm.  Why do you think the algae and plants seem to be growing so well?  What might the farms have to do with it??

from:  and

These rivers are also near a farm, but in a town where there are strict rules about preventing fertilizers and wastes from running off of the land into streams.  Do you see much algae growing in these streams?


from:  and

Here is a view of Lake Erie photographed from space.  The green areas are algae blooms in the lake water.


Here is the Mississippi River Delta (where the Mississippi empties into the Gulf of Mexico) photographed from space.

Water after being cleaned by a Denver waste water treatment plant in the Platte River.  Do you think Denver Water removes excess nutrients somehow??


    Remember, these nutrients are natural elements and compounds.  They are found in organisms in nature also, not just in that sack of fertilizer in your garage.  Producer organisms need them to survive, so these nutrients are not all bad as the above pictures may have you thinking.  When organisms die in nature, the process of decomposition releases those nutrients back into the ecosystem where they can be used again.  If producer organisms such as a plant or algae are nearby, a decaying animal may provide tremendous amounts of nutrients for the growth of that producer's cells.  Assuming the plant is close enough to come into contact with those nutrients that is!  If an animal dies and is somehow carried away, or buried out of reach of producers, the nutrients will be unusable.

So plant nutrients are natural substances.  They help plants and algae grow.  Helping producers to grow seems like a good thing, so why are algae blooms bad??

Click here:  Harmful Algae Blooms