module 1 - the physical soil Flashcards
what do plants require from soils (4 things)
support
oxygen
water
nutrients
What is soil fertility?
considers the physical (composition), chemical (processes and CEC) and biological (microbes) fertility
inorganic material in soil is
gravel
sand
silt
clay
organic material in soil
bacteria fungi roots animals humus
what is soil texture describing
prominent particle size only refers to particles less than 2 mm in diamtre
size and texture of clay
< 0.002 mm feels plastic and sticky when wet
size and texture of silt
> 0.002 - 0.06mm feels smooth or silky
size and texture of sand
> 0.06 to 2 mm feels gritty
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
how does texture affect water movement
quicker through coarse soils as pores are larger
how does texture effect areation
fine textured soils are poorly drained and thus have poor aeration due to the lack of macropores
how does texture effect water retention
better in fine textured soils sandy ones at risk of drought due to large presence of macropores
how does texture effect ease of tillage
clay is often difficult to cultivate
how does texture impact compaction
fine and intermediate texture soils most at risk for compaction
how does texture effect erosion
sandy soils most at risk for erosion due to weak particle cohesion
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
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
A bulk density value of above 1500 kgm3 suggests…
soil is compacted enough to limit root growth
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
A macro-porosity greater than 0.08 to 0.1 is desirable for ….
adequate drainage and aeration
if macroporosity is less than 0.05 what happens..
have issues with drainage and aeration
when does volumetric water content = porosity
when the soil is saturated
what is field capacity
content of water in soil after the excess has drained away
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
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
what is hydraulic conductivity
the rate at which water moves through the soil
what does soil temp effect
seed germination and growth rate
microbial population
accumulation and depletion of om
rate of chemical recations
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
soil consistence means
resistance to deformation or rupture it is dependant on water content of the soil
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
damping is
the decrease in range between max and min temp due to energy being absorbed as it moves down the soil profile
how to calculate readily available water content
(volumetric water content at feild capacity - VWC at SP)/ root depth imm = …..mm
how to caculate total avaliable water content
(VWC at FC - VWC at PWP)/ root depth in mm= ….mm
