Ph Flashcards Preview

Soils II > Ph > Flashcards

Flashcards in Ph Deck (13)
Loading flashcards...
0

What things can Ph effect?

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

1

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-)

2

What is neutralization?

When acids and bases react to form water and a salt

3

Why is pure water neutral

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

4

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

5

What is the optimum soil Ph range for most plants

Ph 6.0 - 7.0

6

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
-Hydrolysis
-Nitric acid from lighning deposits
-Volcanic activity deposits sulphuric acid
-oxidation of ammonium based fertilizers
-Deposition of acid rain resulting from industrial pollution

7

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

Active
-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
Exchangeable
-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
Residual
-Comprises of all bound aluminum and hydrogen in soil minerals. Least available of all pools.

8

What is the buffering capacity?

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

9

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.

10

What pH range do most soil organisms prefer?

5-8

11

Which nutrients tend to be leached at low pH?

Ca2+, Mg2+, K+, Na+

12

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