Soil Surface, Acidity and Nutrients

Question 1

What does colloidal material of soil determine?

Answer 1

Soil chemistry, nutrients for plant growth and those toxic

Question 2

Colloids

Answer 2

Particles larger than molecules yet small enough to remain microscopic

Question 3

Why do colloids remain in suspension in liquids?

Answer 3

Electrostatic properties and specific surface area

Question 4

What are electrostatic charged elements of sols?

Answer 4

Soil humus, clay minerals

Question 5

Two groups of silicate clays?

Answer 5

1:1 with one lay silica then one Al hydroxide, and 2:1 with two silica layers

Question 6

What does silica layer ratio determine?

Answer 6

Physical properties like shrinking/swelling in response to mooisture and different charge characteristics

Question 7

How is OM categorised?

Answer 7

Humus strictly humic compounds whilst others products of decompostion

Question 8

What groups compose OM?

Answer 8

Hydroxyl, carboxyl, phenol and benzene

Question 9

What are the divisions of Humus?

Answer 9

Fulvic acids
Humic acids

Question 10

How do humus and clay differ?

Answer 10

Size, shape, composition and electrostatic charge

Question 11

Isomorphic Substituation

Answer 11

This is where purity of a substance is impeded by introduction by another element, changing charge imbalance

Question 12

What structures do silica in clay form?

Answer 12

Tetrahedral

Question 13

Dissasociated hydroxyl in soils…

Answer 13

Without dissociation from water…

Question 14

How doese hydroxyl react in soils?

Answer 14

H in OH-R disassociate leaving a negatively charged O-R

Question 15

How do ions relate to colloids?

Answer 15

Decreasing tightness further from the charged surface

Question 16

Layers of ion cloud of colloids?

Answer 16

Innermost stern layer whilst outer diffue layer

Question 17

Cation Exchange Capacity

Answer 17

Is the total negative charges within a soil adsorbing plant nutrient cations

Question 18

What does CEC determine?

Answer 18

Ability to supply nutrients like K, Ca and Mg

Question 19

What does high CEC mean?

Answer 19

High colloidal particle concentration

Question 20

What does CEC measure?

Answer 20

Amount of variable and permanent exchange surfaces a soil has

Question 21

Why do anions leach?

Answer 21

Repulsion

Question 22

Wjhat characteristics does soil acidity determine?

Answer 22

Variable charge nature, nutrient availability, microbial activity and toxin release

Question 23

How does acidity indicate cations present?

Answer 23

Acidic soils have high exchangeable ions like Al, whilst alkaline more Na, Ca and Mg

Question 24

Why is Al toxic?

Answer 24

Binds colloids and prevents soil ability to retain base cations, resulting in stunted root development through mitotic inhibition.

Question 25

How can Al be indicated?

Answer 25

Brown stubbly root in upper horizons, inhibiting water uptake, increasing drought suceptibility

Question 26

Types of acidity

Answer 26

Active being total H stock in solution
Exchangeable is H and Al within the diffuse layer, moving easily within solution
Residual is H and Al locked tightly to colloids

Question 27

Buffering Capacity

Answer 27

This is the ability of soils adjustment to change in ionic composition of soil solution

Question 28

Most important macronutrients?

Answer 28

Nitrogen, Potassium and Phosphorous

Question 29

Nitrogen

Answer 29

5% inorganic, mainly ammonium, nitrate and nitrite, organic material mineralise by microorganisms before avaialble to plants

Question 30

How can Ammonium become available?

Answer 30

Fixation into 2:1 clay mineral structures, where up to 20% of nitrogen can become fixed

Question 31

Why is potassium important?

Answer 31

Disease resistance, photosynthesis, stomatal aperture regulation

Question 32

Importance of phosphorous?

Answer 32

Photosyntehsis, nitrogen fixation, crop growth and root development

Question 33

What does phosphate availability lower with?

Answer 33

Acidic and alkaline conditions through coupling with hydrous oxides of Al and Fe, forming insoluble compounds