ENVS2 Practical Skills

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Lorena Stokes
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ENVS2 Practical Skills Soil Analysis A knowledge of the physical, chemical and biological properties of soil can help with agricultural planning and management.

1 ENVS2 Practical Skills Soil Analysis A knowledge of the physical, chemical and biological properties of soil can help with agricultural planning and management. There are a range of test that can be done that investigate the soils mechanical properties, chemical properties and biological properties Mechanical properties formation of peds (structure), depth and texture Chemical Properties provision of nutrients in the soil structure which is linked to texture, ph Biological Properties within the structure, such as detritivores, bacteria and fungi Usually soils are dug with a spade (to dig a pit) or sometimes and auger to dig a core. This reveals the depths of horizons. Usually permission from the landowner would need to be sought and samples collected only limited to a few handfuls (on which ph, structure and texture can be later deduced). Samples collected will need to be placed in a polythene bag and labelled (with site number, location and depth). Sampling The sampling strategy can either be by transect, quadrant or point and through a random, systematic or stratified sampling approach (see below). Soil Tests i) Texture: Testing for soil texture assesses for the proportions of different sized mineral fractions i.e. the British Soil Survey use the following - clay (<0.002mm), silt (0.002mm-0.02mm) and sand (0.02mm-2mm). Two methods exist sieving and sedimentation:

2 a) Sieving: an oven dried (24hrs) sample is crushed and placed on the upper sieve of a vertical stack of sieves that are arranged from coarse to finer going down the stack (NB. Remove any living organisms first). The stack is then shaken by hand by rotating the stack and gently patting the sieves so that finer particles pass through each grade of the mesh. A collection tray collects the finest material at the bottom of the stack. When no further movement of particles occurs (after 5 mins) then the contents of each sieve can be weighed on a pan top balance and their percentage contribution can be calculated (use x/total x 100). Or even easier, 100g of a sample can be weighed out to start. The results are then plotted on a soil triangle to help classify the soil type (see below). b) Sedimentation: A dried soil sample is taken and the obvious particles greater than sand (>2mm) and organic matter are removed. Crush the soil and add to a measuring cylinder up to half full level. The add water to the remaining level of the cylinder. A bung is added to the top and the soil sample is shaken for a fixed period of time to agitate the particles into suspension and fully mix the soil. The container is then allowed to stand on a flat surface free from vibration or disturbance and the time is started. 1 minute of settling will yield the sand fraction and the volume can be recorded. 8 hours - silt 5 days clay c) Soil rolling test: *NOT ON SYL but fun!* For want of a better name! Take a wet handful of soil and squeeze it until no more water comes out. Work it in your hands for about half a minute. Then try and press it into shapes and working towards a bent worm.

3 Shape Cone Ball Worm / roll Bent worm / roll that cracks Smooth bent worm Texture Sand Sand Loam Loam Clay Loam Clay ii) Structure (Peds) must be tested before texture! Can be analysed by soil profiling looking at the arrangement of each layer into different peds. The thickness of each horizon can be measured, photographed and sketched and details of the texture added to the diagram by using above soil rolling test technique. To work out the 4 main types of ped, crush damp soil in your hand and then spill it onto a piece of paper. Most soils consist of peds which are aggregates of particles joined by glue like colloids of humus and clay minerals. For kinds are recognised based on their size, breadcrumb sized crumb; thin at edges and thicker in the middle and orientated horizontally platy, Polyhedral large shapes blocky; and columns with blunt faces columnar. iii) Biological Activity: Uses pooters and Tullgren funnels and earthworm extraction. Pooters are a small mouth operated collector used to extract invertebrates in the soil leaf litter layers. Tullgren funnels are pieces of equipment that either use a light or heat source, invertebrates in the soil leaf litter can be extracted as they move downwards away from the raised temperature or light and fall into the collection chamber. Earthworm extraction is awkward and is time consuming but the easiest way of extracting them from soil is to use water containing a chemical irritant such as methanol or detergent. There are many problems with this method of extraction: deeper worms in the subsoil may be unaffected; larger worms my respond to chemicals differently to smaller ones and some worms may escape sideways in the soil and not rise to the surface. iv) Soil ph:

4 By Colourimetry: Either use ph paper which is absorbent paper (like blotting paper) impregnated with universal indicator solution. Dip the paper into the test solution and compare with standardised colour scale charts. This is fairly subjective as it depends on your colour vision. Secondly you can use soil ph testing kits which use universal indicator that changes its absorption of light at different wavelengths depending on the ph. The colour change is predictable and it to can be compared to a reference chart. This too is simple but judging the colour can sometimes be difficult. For either of these tests follow the standard soil ph testing method: 1. Use a measuring cylinder to add 2.5cm 3 of soil to a test tube. 2. Add 1 cm 3 of barium sulphate (BaSO 4 ), which helps the particles to settle, especially clay as it is a flocculent this clears the sample. NB. Barrium Suphate is toxic do not ingest and wash hands thoroughly after use! It comes from the mineral barite (barytes). 3. Add 3.5 cm 3 of distilled water. 4. Add 10 drops of universal indicator (if using ph paper miss this step out) 5. Apply the bung to the tube and shake well leave to stand for 15 mins. 6. Compare the colour to the standard chart or at this stage if using the ph paper method test with paper. By use of electronic ph prope: This is a simple way to get a quantitative reading usually accurate to 0.1 ph. However, it is important to ensure that the reading is representative of the true ph and to obtain an accurate measure you must follow the method below to ensure calibration: 1. Calibrate the ph meter by using a 7.1 ph buffer (known ph) solution. In this instance it is ph neutral. 2. The prope should be allowed to stabalise i.e. until the numbers stop changing at this point use the skrew driver to tune the prope to the correct ph. 3. The probe should be both inserted into the buffer solution and the sample solution as prepared in the above method to a standardised depth. I d recommend just covering the probe. 4. After using a soil sample the probe can be washed with distilled water and dried before inserting back into the known buffer solution, thus avoiding contamination to this buffer. (v) Soil Moisture Content: Is ccalculated as a percentage of the soil by taking the wet soil mass (g) dry soil mass (g) / Wet Soil Mass (g) x 100. Follow the method below: 1. Use an auger, trowel or spade to core the soil. 2. Place it into a labelled sample bag with location no on.

5 3. Large mineral particles, organic detritus such as leaves and twigs are removed as well as living organisms. 4. A crucible is placed on a pan top balance and tare off. 5. A standard mass of soil is weighed out 6. The basin is heated in a soil oven or using a Bunsen on blue flame for 24 hrs (or until a constant mass is reached see point 8). 7. The basin is reweighed 8. Keep heating until a constant mass is reached. vi) Soil Organic Matter: Can be calculated as a percentage. Dry soil mass Burned Soil Mass / Dry Soil Mass x A crucible is weighed and tare off 2. A dry soil sample (to a constant weight to ensure no moisture see previous method) is placed in the crucible and weighed this is the dry mass 3. Heat the crucible strongly in a furnace or kiln (500 o c) to ensure all organic matter is fully combusted. A Bunsen burner on roaring flame can also be used and the crucible can be left on top of a tripod and gauze. If heating goes above 550 o c, then many clay minerals would begin to break down (metamorphose) and this could yield an inaccurate mass and result in a higher estimate of organic content! You would need to use a clamp and stand to hold a mercury thermometer to test the temperature of the flame. 4. The crucible is re-weighed. 5. Keep repeating stages 3-4 until a constant weight is reached. 6. Use the formula above to calculate the percentage organic matter.

6 KIT 1 TRIPOD & GUAZE 5 CRUCIBLES HP MAT GAS 5 tongues 1 pooter 1 trowel 1 spade Sample bags Pan top balance Paper towels Universal Indicator ph paper ph probe Distilled water 1 litre and rinse bottle Barium Sulphate Mercury thermometer for measureing up to 500 deg c Clamps, stand, boss Funnel and gauze Reading lamp Beakers Chonical Flask

DIRT! APES Laboratory Activity

Name: Part I: Soil Texture DIRT! APES Laboratory Activity Can one determine the texture of soil by examining the particles found in a particular sample? The purpose of this activity is to determine the