Research methods soil analysis Flashcards
what must you do so soil be be analysed in a lab?
must be representative sample
what can be used to get a representative soil sample?
soil auger that collects cross sectional area and depth
what is the issue with collecting soil samples with a trowel?
produces less representative samples that cannot be compared with other samples reliably
how can you measure soil temperature?
using a soil thermometer
what is the method for using a soil thermometer?
must have a protective metal tube to prevent it breaking
push thermometer into a standard soil depth (10cm)
protect thermometer form direct sunlight
leave it until alcohol liquid stops moving and a constant temperature is shown
temperature read will the thermometer is still in soil
what does soil texture assess?
proportions of the mineral particles in different size categories
what are the size categories for soil?
sand
silt
clay
what two methods are sued to measure soil texture?
soil sieves
sedimentation
what is the method for soil sieves?
stack of sieves assembled in mesh sizer order coarsest at top
dry crushed soil sample placed on top sieve
stack is shaken by hand for 2 minutes
particles fall until they cant fit through the mesh gaps
each portion is weighed and % composition calculated
wet sieving possible but sub-soil must be dried before weighing
what will the top sieve contain?
mesh size >2mm
twigs
pebbles
what will the second sieve contain?
0.02-2mm
contains sand
what does the third sieve contain?
0.002-0.02mm
silt
what does the base container hold? (sieve)
clay
what is the method for sedimentation?
large objects removed using 2mm hand sieve or by hand
soil crushed so particles are separated
measuring cylinder half filled with soil and then topped with water
cylinder sealed and shaken by inverting
suspension allowed to settle
total depth settled soil components measured after 2mins, 2 hours, 2 days
proportion of total volume each texture category is then calculated
what is a soil triangle?
triangular graph used to display the combined proportions of the three mineral soil components
how can soil water content be estimated?
noting the mass drop of a weighed soil sample when the water it contains is evaporating by heating
what is stage one of soil water content practical?
soil collected using standard method (soil auger)
what is stage 2 of soil water content practical?
soil sample placed in sealed bag to prevent water loss by evaporation
what is stage 3 of soil water content practical? (Removal)
large mineral particles, organism are removed
what is stage 4 of soil water content practical? (Basin)
soil sample placed in pre weighed evaporating basin and then re weighed to see start weight
what is stage 5 of the soil water content practical?
basin heated to 100*c for 24 hours
what is stage 6 of the soil water content practical?
basin reweighed
what is stage 7 of the soil water content practical?
stage 5 and 6 repeated until constant mass reached
how do you calculate % water content?
(change in soil mass/ wet soil mass)x 100
how can soil organic matter be estimated?
heating the dried soil to burn off organic matter
what is done before doing the soil organic matter content practical?
follow stages 1-7 of soil water content method
what is stage 1 of soil organic matter content?
dry soil sample placed in pre-weighed crucible which is reweighed
what is stage 2 of the soil organic matter content?
crucible heated strongly in furnace or with Bunsen burner
what is stage 3 of soil organic matter?
crucible reweighed after burning (charcoal of soil)
what would happen if when testing for soil organic matter temperature went above 550*c?
calcium carbonate would breakdown releasing carbon dioxide giving an inaccurate result as mass reduction wouldn’t just be organic matter
what is stage 3 of soil organic matter? (Repetition)
stage 1 and 2 repeated until constant mass reached
then % organic matter calculated using % change formula
what is soil bulk density?
mass of dry soil per unit volume
how can the volume of a soil sample be controlled?
using a soil auger of known cross sectional area and pushing in into chosen soil depth
what methods are there to measure pH?
universal indicator solution
universal indicator paper
electronic Ph meter
what is the range for pH?
0 to 14
how does universal indicator solution work?
pH indicator chemicals absorb different light wavelengths
colour change predictable
pH estimated using colour chart
why are colour charts for pH subjective?
relies upon judgment of colour
what is stage one of the universal indicator solution method? (Soil)
add 2.5cm*3 of soil to test tube
what is stage two of the universal indicator solution method? (Barium sulphate)
add 1cm*3 barium sulphate
helps soil particles settle
what is stage three of the universal indicator solution method? (Water)
add 3.5cm*3 distilled water
what is stage four of the universal indicator solution method? (Drops🧪)
add 10 drops universal indicator
what is stage five of the universal indicator solution method? (Bung)
firmly push bung into tube
what is stage six of the universal indicator solution method? (Shaking)
shake thoroughly and leave to stand for 15 mins
what is stage seven of the universal indicator solution method?
compare solution colour to colour chart
what are universal indicator papers?
strips of absorbent paper impregnated with universal indicator solution
dipped into test solution and colour change compared against chart
what is the method for universal indicator paper on soil sample?
same as UI solution test but paper dipped into settled solution instead of adding UI
what is the method for UI paper on water samples?
simply dipped in water and compared with colour chart
what is it important to remember when testing pH electronically?
results are accurate, representative and collected using standardised technique
calibrated using known pH solutions
should be left to stabilise to give stable readings
probe inserted to standard depth
what is the limitation of electronic pH meters?
need to be regularly calibrated with buffer solutions
less convenient then UI paper
