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Transcript of pH
Tests for both soil and water can indicate if amendments are needed.
pH stands for potenz Hydrogen
The pH scale is a measure of how Alkaline or Acidic something is
The pH scale - the potential energy of Hydrogen ions
Most nutrients plants need dissolve and become available most easily when the pH is between 6.0 and 7.5.
Soil pH can range from pH 3-10
There are a few common amendments for soil. Usually soil will be neutral or too acidic.
Use limestone or
"lime" to make an acidic soil more alkaline.
Wood ash also raises an acidic pH.
To lower a basic pH add Sulfur.
Acids have H+ ions
Bases have OH- ions
Acids have hydrogen ions that are positively charged because they are missing an electron.
If your water is very acidic or you frequently have acid rain, you can add amendments to the soil to compensate.
This needs to be re-applied every couple of years.
Amending Acid soils
Peat Moss lowers a basic pH, but isn't a great amendment to use on a large scale.
The pH of the rain in Hawaii is very acidic because of the pollution from the volcano.
What affects soil and water pH?
The parent rock or material the soil came from may have an alkaline or basic pH.
Acid rain is caused by pollution that has sulfur oxides in it. Frequent acid rain will acidify soils.
Groundwater will tend to be neutral. If you live in Hawaii and your soil gets a lot of rainwater, you may need to amend your soil with Lime or wood ash.
Amending alkaline soils
If we go outside of a narrow range of pH, we die!
Ever get achy muscles from working out?
That's lactic acid - H+ ions making you feel the burn!
Nutrients have a charge, too. Ions in the soil can bond to the nutrients, and make them unavailable for plants!
At extreme pH levels, a flood of nutrients might be released, a toxic dose of nutrients might poison the plant.
Atoms have a positive charge in the middle, (protons) and an equal number of electrons that orbit around them and have a negative charge
Atoms are balanced in their charge, with equal positive and negative parts.
Most atoms have a neutral charge.
To answer this, we need to go all the way down to the atomic level.
Ions are atoms that are imbalanced, and have a positive or negative charge.
The lower the pH the more acidic.
0 is the most acidic.
The higher the pH the more alkaline something is.
14 is the most alkaline.
The middle of the scale, 7 is neutral.
Water is usually neutral.
What are acids and bases?
What is acidity or alkalinity?
pH measures how many Hydrogen or Hydroxide ions there are in a substance.
Atoms don't like being imbalanced, and want to bond to things to neutralize their charge.
Bases have an OH- molecule, meaning they are negatively charged, and want to give away an electron.
These ions will try to bond to anything that has an opposite charge.
This is why battery acid will burn your skin!
Or why bleach will burn your skin.
You can digest your food because stomach acid breaks it down.
Soap cleans your hands better than water because it is alkaline, and the ions grab onto dirt and pull it off your skin.
Every number on the scale is 10 more or less than the number before.
This is why soap will clean your hands, but not burn them like bleach.
This is why lemonade tastes good but battery acid will burn you.
If you were to measure the pH of our bodies you would find we are a little alkaline.
For plants, we test the
, because pH makes a big difference in how plants can absorb nutrients.
Why does soil pH affect plant nutrition? ! ?
Some nutrients are positive and some are negative.
Which soil pH is best for plants to get all of what they need?
You can think of ions holding nutrients in the soil the way a magnet sticks to another magnet.
How much pH matters
pH - The potential energy of Hydrogen ions
Soil commonly becomes too acidic.
A buffer grabs some of those H+ ions and keeps them from sticking to nutrients.
That means there are an increasing number of H+ ions in the soil solution.
So we know very alkaline or acidic soil makes it hard for plants to absorb nutrients, why else does it matter?
Microorganisms have a tough time living in overly acidic or alkaline soils.
That means organic matter decomposition will be slower, bacteria that fix nitrogen will work slower, and beneficial fungus will have a tougher time helping plants
Organic material is the best buffer. Clay soils also resist acidification.
This helps neutralize a low pH.
Regular application of Nitrogen fertilizers can acidify soils. Ammonium fertilizers (NH4+) release H+ ions into the soil when NH4+ is oxidized to NO3- by bacteria.
Generally, for the amendment to be effective, it is "worked into" the soil to a depth of 6 inches.
pH measures two types of ions
Ions are atoms that have too many or two few electrons
Because atoms like to be balanced, having an extra electron or missing an electron will make these atoms stick to things if they can.
For gardening we measure how many of these ions are in the soil.
-Reacts with some metals to produce H2
-Slippery to the touch