Acidity & Alkalinity
This ion, released from rainfall, leaching, nitrification, and fertilizers, is the most common cause of soil acidity.
What is H⁺?
This condition occurs in arid climates where evapotranspiration exceeds precipitation.
What is salinity?
This process—rapid in O₂, slow without it—breaks down organic materials into simpler compounds.
What is decomposition?
This form of nitrogen makes up 78% of the atmosphere.
In soils with low pH, phosphorus commonly reacts with this metal ion, making it unavailable.
What is Al³⁺?
This mineral parent material is a major natural source of alkalinity in soils.
What is calcium carbonate (CaCO₃)?
High sodium soils with dispersion problems can be improved by adding this amendment.
What is gypsum (CaSO₄)?
These organisms, such as bacteria and fungi, “wake up” when fresh litter arrives, temporarily dominating decomposition.
Who are r-strategists?
This process uses microorganisms and the enzyme nitrogenase to convert N₂ → NH₃.
What is Biological Nitrogen Fixation?
This is the primary form of P taken up by plants.
What is orthophosphate?
This form of acidity is measured directly by pH and reflects H⁺ in the soil solution.
What is active acidity?
This measurement (EC, ESP, or SAR?) indicates total soluble salts in soil.
What is EC?
A C:N ratio below this value results in net mineralization.
What is 25:1?
Overwatering often causes this loss of nitrate as microbes convert NO₃⁻ to N₂ gas.
What is denitrification?
This process occurs when P is bound by Fe, Al, or Ca minerals, reducing its availability.
What is P fixation?
This aluminum process releases H⁺ and increases soil acidity when Al reacts with water.
What is hydrolysis?
Soils with high EC and high ESP are classified as this soil type.
What are saline–sodic soils?
This complex plant polymer slows decomposition and increases resistance to decay.
What is lignin?
This industrial process fuses N₂ and H₂ to produce NH₃ using high heat and pressure.
What is the Haber–Bosch process? (Industrial fixation)
Helps increase nutrient and water acquisition
Primary mechanism of increased nutrient acquisition is increased adsorptive surface area
symbiosis between plant roots and ____ fungi
What are mycorrhizae?
These climate conditions—hot, wet environments—lead to the strongest leaching and highest acidity.
What are tropical climates?
List 3 different liming materials
Limestone, burned lime, hydrated lime, basic slag, wood ashes.
What is anaerobic and aerobic
Aerobic – rapid enzymatic oxidation of OM in the presence of O2, releases CO2 and lots of energy.
Anaerobic: slow, partial oxidation of organic molecules in the absence of O2 releasing CO2 and other gases (CH4 , H2S, N2O), small energy release.
This Hawaiian soil order is an exception to nitrate leaching because it has positively charged Fe/Al oxides.
What are Accudox (Oxisols)
Name P fixation by soil order
Bonus: Name the order of the minerals
Andisols >> Oxisols > Ultisols >> Mollisols > Vertisols > Entisols
Bonus: Amorphous >> crystalline Fe/Al oxides > kaolinite > smectite