soil testing methods.ppt
TRANSCRIPT
8/10/2019 soil testing methods.ppt
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Soil Testing Methods
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Three approaches
Observations in the field
On-site measurements
Laboratory measurements
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Observations in the Field
Field observations of properties which can be observed after digginga soil pit
Semi-quantitative assessments of properties rather than direct
measurements.
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On site Measurements
On-site measurements using equipment inserted into soil, withoutsignificant disturbance of the soil.
This approach applies particularly to soil water studies.
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Laboratory Analysis
Measurements made in the laboratory on soil samples taken fromthe field.
Sub-sampling down to an analytical sample also occurs
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Field investigation
soil pits
expose the soil profile and horizons
allow field testing of parameters that would be destroyed bycores
in-situ testing devices semi-quantitative assessments
field data minimizes sampling error
does not guarantee reliable or even consistent data soils have very poor homogeneity
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Soil Pit
from www.drm.gov.au
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Choosing Sites for Soil Pits
Avoid
areas close to gateways, paths and tracks
headlands of arable fields (the outer 10 m)
sites where straw or fertilizers have been stored
sites used for localized burning of crop residues or hedge trimmings
old field boundaries where a hedge or bank has been removed andthe land levelled
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Choosing Sites for Soil Pits
soil varies spatially (from one place to another)
some properties vary in time
eg nutrient levels, moisture others are more permanent
horizon depth, texture, stone content and ion exchange capacity
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How do we Sample Soil?
Is it just digging holes?
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Sampling questions
How many samples do I take?
Do we composite lots of sub samples?
How deep do we take the samples?
Do we replicate the sampling?
What quality control do we need?
What tools do I need? How do we transport, store and prepare the samples?
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Information we need to know
Why are we analysing the soil?
Surveys, chemical analysis etc.
How large is the area of interest?
Large areas require lots of sampling
Do we know the soil profile at all?
If we don’t, how deep do we sample?
What are we analysing the soil for?
Physical, chemical or biological parameters
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Amount of sample
depends upon;
Time constraints
Topography
Cost factors
Reasons for sampling There are no specific guidelines
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Soil Sampling
undisturbed stratification:
remove a core with all horizon information retained, eg withauger
disturbed stratification
no attempt to keep the vertical connection between horizons, eg with a shovel
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Soil Sampling
How many samples do we take?
At least 20 single samples per 10 000m2 must be taken with anearth boring tool (or spade) and combined to a mixed sample.
To what depth do we sample?
The usual sampling depth is up to 20 cm in arable land or 10cmin pasture. Undisturbed soil samples are obtained with a cuttingcylinder with minimum capacity of 100cm3 .
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How do we sample?
test lot random diagonal line cross line
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Sampling using Augers
pressed and rotated into the soil to take samples from depthincrements of between 15 and 20cm.
samples are 'disturbed' to varying degrees
observations that can be made on the samples will be restricted
colour, texture, stones, roots and horizon depth can be recorded
soil structure cannot
special coring equipment is required to obtain 'undisturbed' samples
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Sampling for lab testing
normal sampling depth for horticultural and tree crops is 0-15 cm
deep sampling down to 60-100 cm may be necessary to better assesssoil salinity, acidity, S, and mineral N status
sampling depth must be recorded
protocols relevant to important crop and soil tests should befollowed
usually involves making a composite from around 15 to 30 sub-
samples from the area in question
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Transportation, preparationand storage of samples
Now that you have your soil samples, what do you do with
them?
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Laboratory Preparation of Samples
should be kept cool or cold between during transport
may be air-dried remote from the laboratory (max. 40C) whenmoisture content is not required
breaking up any large cores on a clean surface
remove rocks by hand or sieving
retain a representative portion in a sealed polyethylene bag or
'moisture container' for moisture determination
sample size reduction: coning and quartering or riffler
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Laboratory Preparation of Samples
Next spread the soil samples on drying trays (if applicable) and air-dry at up to 40C.
When the soil is thoroughly air-dry, mix, roll, and/or grind.
Retain the <2mm fraction, preferably in an air-tight plastic or inertcontainer, for subsequent laboratory analyses.
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Laboratory Preparation of Samples
When required, determine the weight percentage (oven-dry basis) ofthe residual >2-20 mm size fraction.
When fine grinding is specified, take a representative sub-sample(usually around 30g) from the <2 mm portion.
Pass the entire sub-sample through the required mill and store in asmall air-tight container.
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Coning & quartering