I'm going to start with four tables that will be the basis for my discussion.
Elements Essential to Human Beings
(by volume)
- Oxygen
- Carbon
- Hydrogen
- Nitrogen
- Calcium
- Phosphorus
- Potassium
- Sulfur
- Sodium
- Chlorine
- Magnesium
- Iron
- Manganese
- Iodine
- Silicon
- Florine
- Copper
- Zinc
Elements Essential for Plant Growth
- Carbon
- Hydrogen
- Oxygen
- Nitrogen
- Phosphorus
- Potassium
- Sulfur
- Calcium
- Magnesium
- Iron
- Zinc
- Manganese
- Copper
- Boron
- Molybdenum
- Chlorine
- Nickel
- Silicon
- Sodium
- Vanadium
- Cobalt
- Iodine
Elements that Make Up the Earth's Crust
(by percentage)
- Oxygen
- Silicon
- Aluminum
- Iron
- Calcium
- Sodium
- Potassium
- Magnesium
- Titanium
- Hydrogen
Constituents of the Atmosphere
(by percentage)
- Nitrogen
- Oxygen
- Argon
- Carbon Dioxide
- Neon
- Helium
- Methane
- Krypton
- Hydrogen
Let's start with the first two lists. The elements essential to humans are very similar to the elements necessary for plant growth. The order of some of the initial elements is slightly different and it's obvious that plants need a lot less chlorine and sodium than humans (in fact, some scientists question whether plants need sodium, or any of the last five elements on that list, at all).
The similarities between the first two lists shouldn't be surprising. Humans get most of what we need from plants. (See my posts on Biology 101: Photosynthesis, 5/17/12, and Biology 101: Cellular Respiration, 5/10/12, for the details of our essential chemical interactions.) Where do plants get these elements? The most important elements come from the air (atmosphere) and the water in the soil. Plants take in carbon dioxide and water and use the carbon, hydrogen, and oxygen from them to create sugars. (Again, see my post on Photosynthesis.) They then use these sugars as the basis to build more complex chemicals (for example, cellulose which makes up plant walls).
Plants also get nitrogen from the atmosphere--but not directly. As I wrote in my last post (Soil Science, 7/20/13), the soil is filled with pores that contain air and water. Bacteria in the soil convert nitrogen (N2) to ammonium (NH4+), and then to nitrite (NO2-) and nitrate (NO3-). These ions (as they're called) are easier for the plant to take up. (A small amount of the nitrogen in the atmosphere is converted by lightning into nitrous oxide--N2O--which gets carried into the soil by the rain and the plants can also take up.) This process of conversion which is so important to plants is called the nitrogen cycle. (There is also a carbon cycle and a hydrologic or water cycle that carbon and carbon dioxide as well as water go through.)
The rest of the elements come through the soil. As I explained in my last post (Soil Science), soil is made mostly of broken down rock. If you look at the table of elements in the earth's crust, you'll notice oxygen is the top element (and is, in fact, in one of the first three categories on all four lists). But the next two mystified me for a while. Silicon is at best a trace and relatively unimportant element for humans and plants and aluminum isn't used by them at all. Then I discovered that silicon and aluminum are bound tightly to the oxygen in the compounds found in rocks. However, the next five elements (iron, calcium, sodium, potassium, and magnesium) are, along with sulfur and phosphorus, the most important elements in living creatures (well, sodium isn't so essential for plants) after the basic carbon, oxygen, hydrogen, and nitrogen. It turns out that these elements aren't so tightly bound to the rock. Ions (parts of compounds that are separated and thus have a charge) come loose. The ions of these five elements (all metals) are positively charged and known as 'cations'. (Negatively charged ions, such as chlorine, are known as 'anions'.) One of the main reasons that humus and clay in soil (see my last post) are so important is that they have negatively charged areas that can hold these metal ions. (This is known as the Cation-Exchange Capacity of the soil and is very important in understanding soil and plant nutrition.) The roots of the plants exchange hydrogen ions (also positively charged) for these essential metal ions.
The whole thing is very delicately balanced and is, of course, circular. (See my post on Thinking in Circles, 1/6/13.) It makes me convinced that the whole earth is just one giant ecosystem. Gaia. We live here--and we live here because of the plants, and the rocks, and the soil, and the atmosphere. It's all connected.
Next, the weather.
Quote of the Day: "We know from science that nothing in the universe exists as an isolated or independent entity." - Margaret J. Wheatley
5 comments:
Love it. Except the part that soil is mostly pulverized rock. Nope. Soil is mostly living and dead critters, with some pulverized rock thrown in. That is why soil is grow-able. Because it is alive. :-)
A crucial point, this.
You're correct. I did better in my last post where I talked about the life in the soil and the organic matter.
However, with the help of the soil life and humus, plants do get their minerals from the pulverized rock, aka sand, silt, and clay, and that was my point. The rocks, the atmosphere, the plants, and us--we're all connected.
:-) Yes, they do. But it seems more and more that the fungi and microorganisms facilitate the transfer of the minerals to the roots... they liquify and perhaps even transmute into friendlier forms the said minerals. (While others make the holes to bring in gases and water to make it all possible, and yet others create the "stable humus" glue that turns the living rock dust into crumbs.)
I wouldn't pick on you if most of us were not so brainwashed by the "soil is pulverized rock, and takes millennia to create" people. I was until recently.
Soil is the wonder of the world.
Um. I just noticed you said the same, shorter. Oh well. Sometimes, I just have to keep on blabbing. Sorry for not reading more carefully!
Don't apologize. You're absolutely correct and we need all the reminders about the soil life we can get.
Thanks for your comments.
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