module 1 - the physical soil

Question 1

what do plants require from soils (4 things)

Answer 1

support
oxygen
water
nutrients

Question 2

What is soil fertility?

Answer 2

considers the physical (composition), chemical (processes and CEC) and biological (microbes) fertility

Question 3

inorganic material in soil is

Answer 3

gravel
sand
silt
clay

Question 4

organic material in soil

Answer 4

bacteria
fungi
roots
animals
humus

Question 5

what is soil texture describing

Answer 5

prominent particle size only refers to particles less than 2 mm in diamtre

Question 6

size and texture of clay

Answer 6

< 0.002 mm feels plastic and sticky when wet

Question 7

size and texture of silt

Answer 7

> 0.002 - 0.06mm feels smooth or silky

Question 8

size and texture of sand

Answer 8

> 0.06 to 2 mm feels gritty

Question 9

what ways does soil texture influence soils behaviour (3 ‘s )

Answer 9

• surface area = increased = more reactive (more likely to bond with other particles and retain water)
• surface charge (clays) - can attract cations and some anions
• shape of particles- affects cohesion through contact surfaces and SA and pore size

Question 10

how does texture affect water movement

Answer 10

quicker through coarse soils as pores are larger

Question 11

how does texture effect areation

Answer 11

fine textured soils are poorly drained and thus have poor aeration due to the lack of macropores

Question 12

how does texture effect water retention

Answer 12

better in fine textured soils sandy ones at risk of drought due to large presence of macropores

Question 13

how does texture effect ease of tillage

Answer 13

clay is often difficult to cultivate

Question 14

how does texture impact compaction

Answer 14

fine and intermediate texture soils most at risk for compaction

Question 15

how does texture effect erosion

Answer 15

sandy soils most at risk for erosion due to weak particle cohesion

Question 16

what is soil structure describing and what three things does it focus on

Answer 16

the organisation of particles looking at degree of development, form (ie granular, blocky etc) and size of the most common peds

Question 17

management practises for good soil structure (5)

Answer 17

• cultivate at correct water content
• retain plant residues
• minimise time surface area is bare
• perennial pastures
• add lime to increase ph and enhance soil organism activity

Question 18

A bulk density value of above 1500 kgm3 suggests…

Answer 18

soil is compacted enough to limit root growth

Question 19

why do sandy soils commonly have a greater bulk density to clay (expect when clay is mismanaged) although you would initially expect vice versa

Answer 19

sand particles are large so although there are larger pores the accumalated area of small pores present in clay soils is greater meaning there is less mass per unit of volume and accordingly a sandy soil has more mass per unit of volume meaning its has a greater bulk density

Question 20

A macro-porosity greater than 0.08 to 0.1 is desirable for ….

Answer 20

adequate drainage and aeration

Question 21

if macroporosity is less than 0.05 what happens..

Answer 21

have issues with drainage and aeration

Question 22

when does volumetric water content = porosity

Answer 22

when the soil is saturated

Question 23

what is field capacity

Answer 23

content of water in soil after the excess has drained away

Question 24

what is stress point

Answer 24

point where roots can not extract water at the rate demanded by the leaves. the stomata will close and plant will be under stress

Question 25

what is permanent wilting point

Answer 25

plant has extracted all water they can, water left in soil will be held in micropores which hold it to tightly for it to be extracted due to the capillary phenomena

Question 26

what is hydraulic conductivity

Answer 26

the rate at which water moves through the soil

Question 27

what does soil temp effect

Answer 27

seed germination and growth rate
microbial population
accumulation and depletion of om
rate of chemical recations

Question 28

plastic limit is…

Answer 28

moisture content at which the soil takes on plasticine characteristics it becomes malleable and will take on the shape opposed on it

Question 29

soil consistence means

Answer 29

resistance to deformation or rupture it is dependant on water content of the soil

Question 30

phase lag is ..

Answer 30

soils conduct heat relatively slowly thus at a greater depth it takes longer to heat up or cool down this delay is called phase lag

Question 31

damping is

Answer 31

the decrease in range between max and min temp due to energy being absorbed as it moves down the soil profile

Question 32

how to calculate readily available water content

Answer 32

(volumetric water content at feild capacity - VWC at SP)/ root depth imm = …..mm

Question 33

how to caculate total avaliable water content

Answer 33

(VWC at FC - VWC at PWP)/ root depth in mm= ….mm