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Soil Testing Methods

Soil Testing Methods

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Soil Testing Methods

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  1. Soil Testing Methods Chapter 8

  2. Three approaches • Observations in the field • On‑site measurements • Laboratory measurements Soil Analysis Ch 8

  3. Field Observations • Field observations of properties which can be observed after digging a soil pit • Semi‑quantitative assessments of properties rather than direct measurements. Soil Analysis Ch 8

  4. Field Measurements • On‑site measurements using equipment inserted into soil, without significant disturbance of the soil. • This approach applies particularly to soil water studies. Soil Analysis Ch 8

  5. Laboratory Analysis • Measurements made in the laboratory on soil samples taken from the field. • Sub-sampling down to an analytical sample also occurs Soil Analysis Ch 8

  6. Soil Survey Reports • what kinds of soil exist in an area • described in terms of location, profile characteristics, relationship to each other, suitability for various uses, and needs for particular kinds of management • two major parts in a soil survey report: • the soil map • the narrative Soil Analysis Ch 8

  7. SALIS • NSW soil survey database • Soil And Land Information Service • run by Dept of Natural Resources • Soil Analysis Ch 8

  8. Field Analysis of Soils How can we Analyse Soil in the Field?

  9. Field investigation • soil pits • expose the soil profile and horizons • allow field testing of parameters that would be destroyed by cores • in-situ testing devices • semi-quantitative assessments • field data minimises sampling error • does not guarantee reliable or even consistent data • soils have very poor homogeneity Soil Analysis Ch 8

  10. Soil Pit from Soil Analysis Ch 8

  11. 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 fertiliser have been stored • sites used for localised burning of crop residues or hedge trimmings • old field boundaries where a hedge or bank has been removed and the land levelled Soil Analysis Ch 8

  12. 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 Soil Analysis Ch 8

  13. How do we Sample Soil? Is it just digging holes?

  14. 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? Soil Analysis Ch 8

  15. 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 now 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 Soil Analysis Ch 8

  16. Amount of sample • depends upon; • Time constraints • Topography • Cost factors • Reasons for sampling • There are no specific guidelines Soil Analysis Ch 8

  17. Soil Sampling • undisturbed stratification: • remove a core with all horizon information retained, eg with auger • disturbed stratification • no attempt to keep the vertical connection between horizons, eg with a shovel Soil Analysis Ch 8

  18. Soil Sampling • How many samples do we take? • At least 20 single samples per 10 000m2 must be taken with an earth 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 10cm in pasture. Undisturbed soil samples are obtained with a cutting cylinder with minimum capacity of 100cm3 . Soil Analysis Ch 8

  19. test lot cross line diagonal line random How do we sample? Soil Analysis Ch 8

  20. Sampling using Augers • pressed and rotated into the soil to take samples from depth increments 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 Soil Analysis Ch 8

  21. 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 assess soil salinity, acidity, S, and mineral N status • sampling depth must be recorded • protocols relevant to important crop and soil tests should be followed • usually involves making a composite from around 15 to 30 sub-samples from the area in question Soil Analysis Ch 8

  22. Transportation, preparation and storage of samples Now that you have your soil samples, what do you do with them?

  23. Laboratory Preparation of Samples • should be kept cool or cold between during transport • may be air-dried remote from the laboratory (max. 40C) when moisture content is not required • breaking up any large cores or peds 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 Soil Analysis Ch 8

  24. Laboratory Preparation of Samples Soil Analysis Ch 8

  25. Laboratory Preparation of Samples • Next spread the soil samples on drying trays (if applicable) and air-dry at up to 40C. • When the soil is thoroughly air-dry, mix, roll, and/or grind. • Retain the <2mm fraction, preferably in an air-tight plastic or inert container, for subsequent laboratory analyses. Soil Analysis Ch 8

  26. Laboratory Preparation of Samples • When required, determine the weight percentage (oven-dry basis) of the 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 a small air-tight container. Soil Analysis Ch 8

  27. Coning & quartering Soil Analysis Ch 8

  28. Riffling Soil Analysis Ch 8