Soil Chemistry How nutrients, soil particles and chemistry fit together.
Post on 18-Dec-2015
- Slide 1
- Soil Chemistry How nutrients, soil particles and chemistry fit together
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- Basic Chemical Charges Ions are particles with either a positive or negative charge. Cations are ions with positive charges Ca 2+, Al 3+, H +, Mg 2+, Fe 3+, K +, NH 4 + Anions are ions with negative charges OH -, Cl -, SO 4 2-
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- Acids and Bases (pH) pH is determined by the concentration of H+ (hydrogen) and OH- (hydroxide) H+ is very reactive Acids = high H+ (low OH-) Bases = low H+ (high OH-)
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- Acids and Bases (pH) 1714 Acid high H+ low OH- Neutral equal H+/OH- Base low H+ high OH-
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- Soil pH Many soils have a pH at or just below neutral Some acidic soils may have a pH of 4 or lower pH > 8 is high for a soil Most plants prefer a pH at or just below neutral
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- Where do soils get their pH? Clay particles are negatively charged Organic matter is usually negatively charged This means that positive charges (cations) are attracted to them Clay Particle Organic Matter
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- Where do soils get their pH? Cations (positive charges) could be H+ (making the soil more acidic) Clay Particle Organic Matter H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+
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- Cations could be Cations can be H+ Cations can also be nutrients Potassium (K + ) Calcium (Ca 2+ ) Magnesium (Mg 2+ ) Iron (Fe 3+ ) Nitrogen (NH 4 + ) Clay Particle H+H+ H+H+ H+H+ H+H+ K+K+ NH 4 + Ca 2+ Mg 2+ Fe 3+ Ca 2+ K+K+ NH 4 + Mg 2+ Fe 3+
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- Anions in Soil Positive cations are almost always balanced with negative anions (electrically neutral soil) Chloride Bicarbonate Phosphate Sulfate Nitrate These attach to the positive cations Clay Particle H+H+ H+H+ H+H+ H+H+ K+K+ Ca 2+ Fe 3+ Ca 2+ K+K+ NH 4 + Mg 2+ Cl -
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- Cation exchange Cations can displace each other Depends on concentration in soil (the more there are in the soil solution) Depends on how strongly they are attached to clay or organic matter Clay Particle H+H+ H+H+ H+H+ H+H+ K+K+ NH 4 + Ca 2+ Mg 2+ Fe 3+ Ca 2+ K+K+ NH 4 + Mg 2+ Fe 3+ H+H+
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- Frequent Watering Lowers pH over Long Period of Time Rain tends to be slightly acidic Water is made of H+ and OH- H+ tends to be held very tightly to clay particles Result: Areas that get a lot of rain tend to have more acidic soil!
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- Areas that get a lot of rain tend to have more acidic soil! Clay Particle H+H+ H+H+ H+H+ H+H+ K+K+ NH 4 + Ca 2+ Mg 2+ Fe 3+ Ca 2+ K+K+ NH 4 + Mg 2+ Fe 3+ H+H+ H+H+ H+H+ H+H+ OH -
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- Areas that get LITTLE rain tend to have more basic soils! H+ doesnt displace as many of the other cations present in the soil as in rainy areas. Desert soils tend to be basic! We dont add lime or eggshells (bases) to our soil like they do in the East where soils are acidic. Instead we add coffee grounds (acid) to make our soil more neutral.
- Slide 14
- The POINT? Clay particles and organic matter are negatively charged and attract cations Cations in soil can be H+ or nutrients When there is a lot of rain, H+ cations displace other nutrients making the soil more acidic
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