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Technical Support Soil Indexes How to take a soil sample
Technical Support Soil Indexes How to take a soil sample
| How to take a soil sample |
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| Soil Indexes | ||
The importance of getting a representative sampleThe first point to remember about soil analysis is that any analytical result is only as good as the sample taken. Let us consider one sample taken in a 5 hectare area, that sample might weigh 250 to 500 grams. If it were to weigh 500 g, and we were looking at a soil depth of 15 cm, then that 500 g would be half a kilogram out of 1.8 million kilograms! Of that 500 g, once it reaches the laboratory it will be well mixed and a lot less soil used for analysis. So for a sample to be representative of all that soil, it must be taken carefully. Sampling strategyWhen deciding upon a sampling strategy there are some key points to consider:
How many samples should I take?This depends on the type of soil analysis. Generally, as a simple rule of thumb you should take at least one sample for each area that you are going to manage. For example, you should take one representative sample per field, if you are going to manage nutrients on a field scale. If you know that different areas of the field perform in different ways then you should take a representative sample from each area. If you have a problem area, you should take one sample from the problem area, and one from a good area – to check background levels, so you have something to compare your problem with – a point of reference.It should be noted that the number of samples per field is a trade-off between accuracy and analytical cost. Whilst additional samples cost more money, keeping to one sample as the field size doubles, halves the accuracy. If the sample is for monitoring of soil properties a W pattern of as many cores as possible should be taken through the area in question – avoid irregular patches such as gateways, headlands and trees. See diagram. Samples should be taken before applications of fertiliser or treatment. If it is necessary to sample following an application, a minimum period of 3 weeks should pass before the soil is sampled. How deep should the sample be?This depends on how the soil is to be managed. If a 50 cm deep excavation is to take place, then the whole of the 50 cm should be sampled, if the nutrient is to be applied to the surface and left, unincorporated (as in Permanent Grassland) then there is no point in sampling to this depth.Again a simple rule of thumb – sample as deeply as the soil you are managing. For arable and cultivated soils this is typically 0-15 cm (0-6”) and is related to cultivation depth. For permanent grassland, then a typical depth of 0-7.5 cm (0-3”) is used and this is related to the rate of soil formation and animal penetration. Deeper sampling may be required for mobile nutrients such as nitrogen1, where larger volumes of soil are to be disturbed or where soil nutrient problems are identified at particular depths (mineral layers etc). When should samples be taken?Generally soil nutrient sampling should be incorporated into a quality crop or grassland management scheme.
Tools for samplingEssential tools for soil sampling include:
Samples should be packaged securely and individually labelled – remember they need to survive the transit process which is out of your and NRM’s control! Laboratory Paperwork – why it mattersIt is critical that all samples are submitted with the correct paperwork – this is because the paperwork identifies:
Arable and break crop codesWW Winter WheatSW Spring Wheat WB Winter Barley SBA Spring Barley MB Malting Barley SA Set Aside OR Oilseed Rape WOSR Winter Oilseed Rape SOSR Spring Oilseed Rape PL Ploughed/Fallow UB Undersown Cereal OU Undersown Oats WO Winter Oats SO Spring Oats LI Spring Linseed TR Triticale RY Rye Grassland and forage cropsPP Permanent PastureGZ Grazing HA Hay SI Silage LE Grass Ley HS Herbage Seed RS Grass Reseed MA Mangels FB Fodder Beet BE Field Beans SD Forage Swedes KA Kale FR Forage Rape ST Stubble Turnips LUC Lucerne MZ Forage Maize VegetablesPE PeasCL Calabrese PM Main Crop Potatoes CY Celery PS Seed Potatoes CO Courgettes EP Early Potatoes AU Aubergines CP Canning Potatoes PR Peppers SE Second Early Potatoes PH Rhubarb BR Brussel Sprouts RA Radish CA Cabbage PA Parsley CF Cauliflower LK Leeks CA Main Crop Carrots PN Parsnips ON Onions CU Cucumbers RB Beetroot LET Lettuce BRO Broccoli (Calabrese) BB Broad Beans DB Dwarf Beans RUNB Runner Beans TU Main Crop Turnips Flowers and other specialist crops BU Bulbs
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