Mid Term 2

Question 1

Soil water functions

Answer 1

Essential for photosynthesis
Turgor pressure
Transports nutrients
Helps plant for temperature variations

Question 2

What is hydrogen bonding

Answer 2

Weak interactions between the partial positive charge of hydrogen and with the partial negative charge of oxygen

Question 3

What is cohesion

Answer 3

Sticking of water molecules to each other from hydrogen bonding. Responsible for surface tension

Question 4

What is adhesion

Answer 4

Sticking of water molecules to other molecules

Enables water to “climb” up soil pores - capillary action

Question 5

Forms of water in soil and what they are

Answer 5

Hygroscopic Water - films around clay particles, only form of water found in air dried condition

Capillary water - held on capillary pores (<1mm thick), main form of available water

Free water - drainage or free draining water found in the bigger pores and moves downward by gravity

Question 6

Definition of field capacity

Answer 6

All macro pores have drained, only micro pores are filled. Plants can access this water

Question 7

Definition of permanent wilting point

Answer 7

Any water still in soil is not available, plant wilts and dies

Question 8

Infiltration definition

Answer 8

A measure of the rate at which rain fall or irrigation is absorbed into the soil (in/hr, mm/hr)

Question 9

What are water movements through soil (4)

Answer 9

Gravitational flow

Matric flow

Capillary rise

Osmotic potential

Question 10

What is gravitational flow

Answer 10

Movement of water through saturated soil

Question 11

What Is matric flow

Answer 11

Movement of water through unsaturated soil ( wet to dry)

Question 12

What is capillary rise

Answer 12

Water is pulled upward from water table in micropores by cohesive/adhesive forces

Question 13

What is Osmotic potential

Answer 13

Determined by concentration of solutes in soil water (water flows from zones of low solutes to zones of high solutes) important for root-water interaction

Question 14

Why is water movement important

Answer 14

Soil with rapid internal drainage have higher risk of leaching
Helps determine best drainage plan
Understanding how salinity works

Question 15

Chemical properties of soil (5)

Answer 15

Anion-Cation exchange capacity 
Reaction (pH)
Calcium carbonate content
Salinity and solicits
Soil organic matter

Question 16

Cation exchange capacity

Answer 16

The total number of exchangeable cations a soil can hold

Question 17

Anion exchange capacity

Answer 17

Relative amount of negatively charged anions which can be held by a given weight of soil

Question 18

What is soil pH

Answer 18

Soil pH is a measure of acidity or alkalinity of soil
Seldom go beyond 4-9
Soils become acidic as rainfall leaches away basic cations such as (Ca, Mg, K, Na) while Al and H stay behind making the soil acidic
More rain = more acidic

Question 19

Other factors that affect soil pH

Answer 19

Type of vegetation 
Type of parent material
Amount +type of OM
Amendments
Salinity and sodicity

Question 20

Why are saline and sodic soils alkaline

Answer 20

Not a lot of water movement through soil that causes leaching so basic cations stay in soil making it basic

Question 21

Why do we use lime

Answer 21

Reduces Al and other metal toxicities
Improves physical condition of soil
Stimulates microbial activity
Increases CEC in variable charge soils
Increases availability of several nutrients
Supplies Ca and Mg to plants
Improves symbiotic N fixation in legumes
Improve crop yields

Question 22

How does salinity happen

Answer 22

Occurs when groundwater containing salt is able to reach the root zone or soil surface where it evaporates and leaves an accumulation of salt

Question 23

Conditions required to create a soil salinity problem

Answer 23

1. Soluble salts in subsoil, ground water or both
2. High water tables to carry soluble salts into root zone by capillary action (<6 ft from surface)
3. Plants susceptible to soil salinity (pulses, vegetables, oilseeds)

Question 24

Salinization is a natural process controlled by

Answer 24

Hydrology
Geology
Biological processes

Question 25

What is regional or artesian discharge salinity

Answer 25

Occurs when water within an underlying aquifer is under sufficient pressure to reach land surface. Then water evaporates at surface and salts are left behind

Question 26

What is side hill seep salinity

Answer 26

Occurs where permeable glacial drift overlies impermeable materials such as clay or bedrock Lateral movements eventually intersects a side hill surface Groundwater discharges at this point and evaporation of water leave behind salt at surface

Question 27

What is bathtub or evaporitic ring salinity

Answer 27

Occurs adjacent to wet depressions or sloughs Lateral upward capillary flow from the water table concentrates salts adjacent to the slough, leaving salt in a concentric ring surrounding the slough

Question 28

How do we test for salinity

Answer 28

Electrical conductivity-a measure of soluble salts within the soil 2 methods used to measure EC 1. Saturated paste method 2. Soil:Water ratio method

Question 29

Managing primary salinity

Answer 29

Strategic cropping choices to manage water Reduce tillage Increase soil OM

Question 30

Managing secondary salinity

Answer 30

Strategic cropping choices to manage water Drainage strategies to manage water and leach salts out of soil profile

Question 31

Sodic soils

Answer 31

Characterized by: elevated sodium concentration relative to calcium and magnesium pH usually above 8.5 May be able to manage with gypsum addition

Question 32

Components of soil

Answer 32

45% mineral 25% water 25% air 5% OM

Question 33

Components of OM

Answer 33

33-50% decomposing OM 33-50% stabilized OM <10% fresh residue <5% living organisms

Question 34

What is OM

Answer 34

Generally considered to be plant residue in various stages of decomposition in the soil and... Microflora-bacteria, fungi Microfauna-Protozoa and nematodes Macrofauna-earthworms and millipedes

Question 35

What is decomposed residue called in OM

Answer 35

Humus | Responsible for dark colour in Ah horizon

Question 36

How is humus determined

Answer 36

By measuring the amount of organic carbon in the soil

Question 37

What happens when the C:N ratio is high

Answer 37

Immobilization of soil nitrogen

Question 38

What happens when the C:N ratio is low

Answer 38

New mineralization of nitrogen

Question 39

What is C:N ratio

Answer 39

``` Carbon to nitrogen C:N of plant residue depends on crop type 100:1 wide ratio 15:1 narrow ratio >25:1 net mobilization <25:1 net mineralization ```

Question 40

``` C:N ratio numbers Cereal crop Legume residue Soil humus Microbes ```

Answer 40

Cereal 80:1 Legume 25:1 Soil humus 10:1 Microbes 6:1

Question 41

Starting soil conditions

Answer 41

Modest levels of nitrate Low c/n ratio Low microbial activity

Question 42

What happens when you return heavy amounts of cereal crop residue

Answer 42

Can cause a temporary shortage of mineral nitrogen for crops (why we burn residue in fields)

Question 43

Removal of crop residue why

Answer 43

Common on heavy clay soils where cool wet conditions slow decomposition Removal means loss of vital nutrients such as nitrogen and phosphorus will be lost

Question 44

Factors affecting soil OM levels (7)

Answer 44

1. Natural vegetation 2. Temperature 3. Soil moisture 4. Soil texture 5. Aeration 6. Cropping and cultivation 7. Landscape position