Exam 4 material

percentage composition in soil of Potassium

2.6%

percentage composition in soil of Sodium

2.8%

percentage composition in soil of Silicone

27.7%

percentage composition in soil of Calcium

3.6%

percentage composition in soil of Oxygen

46.6%

percentage composition in soil of Aluminum

8.1%

amorphous material

A material that lacks the long-range order that is characteristic of a crystalline solid. Amorphous materials are either rubbers or glasses

Buffering of soil with a pH of 6.0 would be through which mechanism? Aluminum activity CEC Carbonate activity

CEC

Humus is an important soil colloid. It differs from 2:1 type minerals in all but one of the following characteristics. Structural framework of the particles CEC dependence on soil pH Capable of adsorbing cations Influence on soil aggregate stability Influence of isomorphous substitution

Capable of adsorbing cations

Fine-grained mica, Kaolinite, and Montmorillonite (smectite) are examples of _____ silicate clays

Crystalline

What are the 3 elements in Earth's crust that are essential for plant growth?

Fe Ca Mg

You are working with a soil colloid known to have a reasonably high potassium level, a cation exchange capacity of about 15 cmolc kg-1 of clay and little tendency to swell when wetted. Which of the following is most likely to be the clay mineral in this soil? Kaolinite Chlorite Fine-grained micas (illite) Humus Smectite

Fine-grained micas (illite)

Allophane and Imogolite are examples of _________ silicate clays

Non-crystalline

Which element makes up the most % by weight of Earth's crust?

O

the eight most abundant elements in soils in order of percentage composition in soil

Oxygen O 46.6% Silicone Si 27.7% Aluminum Al 8.1% Iron Fe 5.0% Calcium Ca 3.6% Sodium Na 2.8% Potassium K 2.6% Magnesium Mg 2.1%

_____ is not one of the eight most abundant elements in Earth's crust and in most soils. Iron Potassium Calcium Phosphorus

Phosphorus

Which element makes up the second most % by weight of Earth's crust?

Si

2 Types of Soil Colloids

Silicates & Non-silicates

Which of the following soils would have the lowest pH at 75% base saturation? Soil with a histic epipedon Smectitic soil Soil with an ochric epipedon Oxisols with hydrous oxide minerals Kaolinitic soil

Soil with a histic epipedon

Adsorption

The process of binding or sticking to a surface loose association between soil colloidal particle and water molecule

Nitrogen fertilization is a significant cause of _______ in many cultivated soils.

acidity

The biological liming effects on soil properties include assuring ___________ of required elements and stimulating ___________ activity

balance microbial

The center of the octahedral is generally a ______ such as Al3+, Mg2+, Fe2+, Fe3+

cation

An increase in pH through liming would fall into which category of soil properties?

chemical

soil colloids are _____-sized particles

clay

soil colloids are ____-sized particles that are not visible with a light microscope

clay-sized (< 0.002 mm (2μm))

In order for a material added to soil to decrease pH, it must react in such a way that _____.

exchange acidity increases

Smectite and vermiculite are more prominent in extremely weathered soils than in soils that are modestly weathered. true or false?

false

The high cation adsorption capacity of vermiculite is due primarily to the substitution of Si atoms for Al in the tetrahedral sheet. true or false?

false

a ______ charged cation will be replaced by a __________ charged cation and they must be similar in ______

higher lower size

Of the soil colloids, _____ has the lowest acid strength.

hydrous oxides

colloids have a _______ surface area per unit mass

large

Soils with little clay and hence less buffering by CEC, would require _____ liming material than a clay soil with more buffering by CEC.

less

Cations are _______ held and can exchange with solution cations

loosely

At any base saturation, humus has the _______ pH.

lowest

colloidal surface charge is usually overall, a net _______ charge

negative

Which of the following is NOT a characteristic of soil colloids? high external surface area ability to exchange ions with the soil solution low water holding capacity electro-negative charges very small size

ow water holding capacity

Chemical liming effects on soil properties include increase in ____ and increase in Ca &/or ___ availability.

pH Mg

2 types of colloidal charges (isomorphic charges)

permanent/constant charge pH dependent/variable charge

Increase Ca &/or Mg availability in a soil may increase __________ of other plant nutrients such as N, P, and K and may decrease others such as Fe, Mn, Zn, and Cu.

solubility

One of the physical liming effects on soil properties is that it improves _________ through flocculation.

structure

crystalline clay groups (2) are based on the ratio of

tetrahedral to octahedral sheets

Active soil acidity is a measure of

the H+ activity in soil solution.

In humid regions repeat applications of limestone are needed after a few years primarily because of _____. the release of aluminum ions from the structure of silicate clays the annual loss of calcium and magnesium in drainage waters increases in soil acidity from acid rain increases in phosphate fertilization increased rates of formation of carbonic acid

the annual loss of calcium and magnesium in drainage waters