Soil Testing Methods
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Soil Testing Methods Chapter 8 Three approaches Observations in the field On-site measurements Laboratory measurements Soil Analysis Ch 8 2 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 3 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 4 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 5 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 6 SALIS NSW soil survey database Soil And Land Information Service run by Dept of Natural Resources http://www.dnr.nsw.gov.au/soils/about_salis.shtml Soil Analysis Ch 8 7 Field Analysis of Soils How can we Analyse Soil in the Field? 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 9 Soil Pit from www.drm.gov.au Soil Analysis Ch 8 10 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 11 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 12 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? Soil Analysis Ch 8 14 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 15 Amount of sample depends upon; Time constraints Topography Cost factors Reasons for sampling There are no specific guidelines Soil Analysis Ch 8 16 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 17 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 18 How do we sample? random diagonal line Soil Analysis Ch 8 cross line test lot 19 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 20 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 subsamples from the area in question Soil Analysis Ch 8 21 Transportation, preparation and 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) 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 23 Laboratory Preparation of Samples Soil Analysis Ch 8 24 Laboratory Preparation of Samples Next spread the soil samples on drying trays (if applicable) and airdry 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 inert container, for subsequent laboratory analyses. Soil Analysis Ch 8 25 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 26 Coning & quartering Soil Analysis Ch 8 27 Riffling Soil Analysis Ch 8 28
