module 1 - the physical soil Flashcards Preview

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Flashcards in module 1 - the physical soil Deck (33)
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1

what do plants require from soils (4 things)

support
oxygen
water
nutrients

2

What is soil fertility?

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

3

inorganic material in soil is

gravel
sand
silt
clay

4

organic material in soil

bacteria
fungi
roots
animals
humus

5

what is soil texture describing

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

6

size and texture of clay

< 0.002 mm feels plastic and sticky when wet

7

size and texture of silt

>0.002 - 0.06mm feels smooth or silky

8

size and texture of sand

>0.06 to 2 mm feels gritty

9

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

- 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

10

how does texture affect water movement

quicker through coarse soils as pores are larger

11

how does texture effect areation

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

12

how does texture effect water retention

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

13

how does texture effect ease of tillage

clay is often difficult to cultivate

14

how does texture impact compaction

fine and intermediate texture soils most at risk for compaction

15

how does texture effect erosion

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

16

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

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

17

management practises for good soil structure (5)

-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

18

A bulk density value of above 1500 kgm3 suggests...

soil is compacted enough to limit root growth

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

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

20

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

adequate drainage and aeration

21

if macroporosity is less than 0.05 what happens..

have issues with drainage and aeration

22

when does volumetric water content = porosity

when the soil is saturated

23

what is field capacity

content of water in soil after the excess has drained away

24

what is stress point

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

25

what is permanent wilting point

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

26

what is hydraulic conductivity

the rate at which water moves through the soil

27

what does soil temp effect

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

28

plastic limit is...

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

29

soil consistence means

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

30

phase lag is ..

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