soil testing methods.ppt

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Soil Testing Methods



Three approaches

Observations in the field

On-site measurements

Laboratory measurements



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.



On site Measurements

On-site measurements using equipment inserted into soil, withoutsignificant disturbance of the soil.

This approach applies particularly to soil water studies.



Laboratory Analysis

Measurements made in the laboratory on soil samples taken fromthe field.

Sub-sampling down to an analytical sample also occurs





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



Soil Pit

from www.drm.gov.au



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



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



How do we Sample Soil?

Is it just digging holes?



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?



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



Amount of sample

depends upon;

Time constraints

Topography

Cost factors

Reasons for sampling There are no specific guidelines



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



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 .



How do we sample?

test lot random diagonal line cross line



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



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



Transportation, preparationand storage of samples

Now that you have your soil samples, what do you do with

them?



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




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.




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.



Coning & quartering



Riffling

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soil testing methods.ppt