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Flashcards in Ph Deck (13)
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What things can Ph effect?

-availability of nutrients
-toxicity of certain elements
-functioning of soil organisms


What differentiates an acid and a base

An acid is any compound or ion that can give up an electron (H+)

A base is any compound or ion that can accept a electron (OH-)


What is neutralization?

When acids and bases react to form water and a salt


Why is pure water neutral

because pure water contains equal concentrations of H+ and OH-


By how much does each value on the Ph scale increase with each whole number

For each whole number above 7 the alkalinity will be 10 times more

For each whole number below 7 the acidity will be 10 times more


What is the optimum soil Ph range for most plants

Ph 6.0 - 7.0


List some origins of acidity

-Release of hydrogen atoms under natural chemical processes
-Atmospheric CO2 reacts with water to form carbonic acid
-Organic molecules react with water and cause acid dissociation
-Oxidation of the ammonium form of nitrogen
-Fulvic and fumic acid products of organic decomposition
-Nitric acid from lighning deposits
-Volcanic activity deposits sulphuric acid
-oxidation of ammonium based fertilizers
-Deposition of acid rain resulting from industrial pollution


What are the 3 sources (pools) of acidity in soil?

-Quantity of H+ present in soil water solution. The active pool of H+ is in equilibrium with the exchangeable hydrogen ions that are held on the soils cation exchange complex. Most readily effects plant growth and can be measured using a Ph meter
-Refers to the amount of acid cations (Al+ and H+) occupied on the cation exchange complex. When the CEC is high but has a low base saturation, it becomes more resistant to Ph changes
-Comprises of all bound aluminum and hydrogen in soil minerals. Least available of all pools.


What is the buffering capacity?

A.k.a. reserve acidity. Buffering capacity is a soils propensity to resist changes in Ph.


Why is an understanding of pH important in soil science?

Soil micro-organisms are sensitive to pH and nutrient availability and uptake by plants varies with pH.


What pH range do most soil organisms prefer?



Which nutrients tend to be leached at low pH?

Ca2+, Mg2+, K+, Na+


What happens when a soil drains and dries?

Ph returns to a more normal level as H+ and OH- are reabsorbed onto cation exchange sites