Including the optional sand fractions will refine the calculation. This soilquality.org.au fact-sheet has been funded by the Healthy Soils for Sustainable Farms programme, an initiative of the Australian Government’s Natural Heritage Trust in partnership with the GRDC, and the WA NRM regions of Avon Catchment Council and South Coast NRM, through National Action Plan for Salinity and Water Quality and National Landcare Programme investments of the WA and Australian Governments. Track the lines with the percentages measured and find the spot on the triangle where all three lines intersect. Now it's time to do the math. Standard curve for Mn on an AAS. To evaluate soil texture, use a simple jar test to determine the percentages of sand silt, and clay. The first method, the Jar Method, is the one you'll most commonly find on beginning garden sites. Particle size analysis breaks a soil into texture classes – sand, silt or clay. Where the granules are very clear it is sand, the silt has a tiny bit of texture and the clay will be very dense. Your two fingers will always meet at clay for the remaining percentage, in this case 20%. The sand fraction settles first followed by the silt then the clay fractions. This chart is based on the USDA soil texture triangle, which provides an even higher level of detail when it comes to classifying soil texture. 6. Laboratory analysis of soil texture is laborious and not environmentally friendly. Use pesticides only according to the directions on the label. A Holdrege silt loam, for example, describes the texture of the surface horizon. Soil texture determines the probability of finding a particle with a specific size in the set of all particles. Loam is a textural class representing about one-fifth clay, with sand… The grid on the triangle allows you to move to the left or the right of your position running parallel with either side of the triangle. Good luck! This is the method now used in the Bureau of Chemistry and Soils. The soil textural triangle is used to determine soil type based on sand, silt and clay percentages. The method comprises two parts, dispersion of the soil and separation of the particles into size groups. In soil fertility, coarser soils generally have a lesser ability to hold and retain nutrients than finer soils. Soil texture refers to the relative percentage of sand, silt and clay in a soil. The main target of this analysis is the determination of percentage content of each fraction of clay (< 0.002 mm), silt (0.002–0.05 mm), sand (0.05–2.0 mm) and soil skeleton particles (> 2.0 mm) in total – mineral and organic – soil mass. Oven-dry wt. The soil are extracted successfully. The example shown represents a loam soil texture. Particles greater than 2 mm are removed before analysis. In this method the soil particles are dispersed with a sodium metaphosphate (calgon) and then agitated. A more precise determine of soil texture can be determine from percent sand silt and clay using the soil triangle. (Eds N McKenzie, K Coughlan, H Cresswell) pp 224-239. Image adapted from Hunt and Gilkes (1992). The Robinson pipette method (Pipette) is accurate and precise but time consuming. Figure 2: Cylinder used for fractionation of sand, silt and clay particles. Iron oxides, calcium carbonate and magnesium carbonate should also be removed as they are common cementing agents in Australian soils (Bowman and Hutka, 2002). Use this online tool to calculate a single point texture class based on percent sand, silt, and clay. Bowman GM and Hutka J (2002) Particle Size Analysis. SAC 101 Fundamentals of Soil Science (2 + 1) 2006 It is a guide to the value of the land Land use capability and methods of soil management depends on Texture Particle size distribution/ determination The determination of relative distribution of the ultimate or individual soil particles below 2 mm diameter is called as Particle size analysis or Mechanical analysis. Simultaneously use another finger to trace a line from the 30% silt mark until the two meet. Figure 15. Join our mailing list to receive the latest updates from HGIC. Jar showing the clay layer. Good luck! The three primary soil particles are sand, silt, and clay. The region where these lines intersect indicates the soil type present. The silt percentage is on the right side, with lines extending downwardly, diagonally right to left (see green line). If the percentages of clay, silt, and sand in a soil are known (primarily through laboratory analysis), you may use the textural triangle to determine the texture class of your soil. Adding organic matter to clay and sandy soil can help with: For more information on amending soils, see HGIC 1655, Soil Conditioning – Establishing a Successful Gardening Foundation. 7. basedon previous crop, soil texture, yield goal and sometimescultivar. Soil Physical Measurement and Interpretation For Land Evaluation, Australian Soils and Landscapes An Illustrated Compendium. Silts are typically composed of quartz and small mineral particles such as feldspars and mica, and are between 2 and 20 microns in diameter. Pre-treatment of the soil will allow it to disperse completely. Standard curve for organic carbon on spectrophotometer 3. McKenzie NJ, Jacquier DJ, Isbell RF, Brown KL (2004) Australian Soils and Landscapes An Illustrated Compendium. Jensen JL(1), Schjønning P(1), Watts CW(2), Christensen BT(1), Munkholm LJ(1). In most cases the particles will not be balanced, and the soil will need to be altered by adding organic amendments. Particle size analysis breaks a soil into texture classes – sand, silt or clay. This is commonly called the ‘gravel fraction’. It is important to carry out a soil texture analysis for any garden that you want to plant in. And almost every problem you might run into can be solved or at least improved with compost. Using a mesh sieve or old colander, sift the soil to remove any debris, rocks, and large organic matter (leaves, sticks, roots, etc.). Practical Implications. This should be where clay is 15%. In addition to the chemical properties of the soil, knowing the physical structure and biological response of your soils is essential for proper soil management. Fractionation involves removing each particle size group (sand, silt and clay) from a pretreated soil and water mixture settled in a cylinder (figure 2). Soils that contain a lot of gypsum are normally are pinkish white in color. Clays are made up of secondary clay minerals and oxides/oxyhydroxides of iron and aluminium, and are less than 2 microns in diameter. Meaning of Mechanical Analysis: The mineral component constitutes the largest volume of soil mass and plays a vital role in determining most of the physical properties of soil. Greater than 2 mm and include coarse quartz, rock fragments and cemented material. Soil testing and soil analysis gives the background knowledge on the chemical, physical and biological status of a soil that we need in order to properly manage our soils and crops. Particle size analysis (PSA) determines the relative amounts of sand, silt and clay in a soil. Soil texture classes according to proportions of sand, silt and clay 2. Soil texture is an inherent soil quality property that has a major influence on several other properties that influence agricultural potential (White, 1997). Most soils in South Carolina will require some form of organic amendments. The procedure is a modification of AASHTO Test Method T-88-86. Since the soil's textural classification includes only mineral particles and those of less than 2mm diameter, the sand plus silt plus clay percentages equal 100 percent. The specific gravity depends upon the mass of solids present, which in turn depends upon the particle size. The Soil Test Form requests that you provide the texture of your soil sample. Textural Triangle. Texture class is one of the first things determined when a soil is examined. Using a ruler, measure and record the height of each layer, and the total height of all three layers. Exact estimates of soil clay … There is only an approximate correlation between hand texturing and PSA (McDonald et al., 1998), because hand texturing relies on qualitative interpretation of texture while PSA measures exact amounts of individual particle sizes. Background. The left right and bottom of the triangles are named clay, silt and sand side respectively. This is achieved by allowing the soil particles of different size to settle out of solution at different times (small clay particles take the longest). It is related to weathering and parent material. Standard curve for P on spectrophotometer 4. Soil texture is determined with the help of the triangular texture diagram as shown in Fig 4.1, drawn as follows: First draw an equilateral triangle of sides 10 cm each, divide them into 10 equal parts and mark them 10, 20, 30, 40, 100. The clay percentages are listed on the left side of the triangle. However, unless you have access to professional soil analysis equipment, this level of detail is beyond what is needed for the average gardener. Including the optional sand fractions will refine the calculation. Values presented in this manual TEST METHOD FOR THE PARTICLE SIZE ANALYSIS OF SOILS BY HYDROMETER METHOD 1. Soil texture triangle to estimate the soil type for the site. Soil Texture Calculator Use this online tool to calculate a single point texture class based on percent sand, silt, and clay. You will be able to see the layers pretty well. The soil texture triangle (figure 3) is used to convert particle size distribution into a recognised texture class based on the relative amounts of sand, silt and clay as a percentage, for example: Figure 3: Once soil fractionation is complete a soil textural triangle is used to determine soil texture. Image courtesy of Natural Resources Assessment Group, DAFWA. Not one particle of wasted time. The physical and chemical behaviour of a soil is influenced strongly by soil texture (Bowman & Hutka, 2002), which will vary due to the differences in the type and mineral composition of the parent material, the soils position in the landscape, and the physical and chemical weathering processes involved in soil formation. Soil texture analysis of Katepurna river basin, Akola District, Maharashtra with reference to water resource management Khadri, S.F.R, Sanjay S. Deshmukh Department of Geology, Sant Gadge Baba Amravati University, Amravati-444602 (MS) Abstract In this study an attempt has been made to understand the hydrogeomorphological regime of the Katepurna river basin by utilizing soil texture … Cap the jar and shake vigorously until the soil turns into a uniform slurry. All of this serves one goal—to reduce the operating time you spend for particle size analysis, while at the same time improving accuracy. For a more detailed description of this method please refer to Particle Size Analysis in the Soil Texture fact sheet. The fractions are subsequently dried and weighed and the sand, silt and clay must add Figure 1: Manipulation of soil for field texturing. In most cases the particles will not be balanced, and the soil will need to be altered by adding organic amendments. Measuring Soil Texture in the Laboratory . The size measured for the particles change depending upon which system is used for defining soil particle size classification. Reciprocating horizontal mechanical shaker, capable of 180 oscillations per minute. In most cases the particles will not be balanced, and the soil will need to be altered by adding organic amendments. Soil texture reflects the amounts of various sized particles (sand, silt, and clay) in the soil… Similarly, a sample comprising primarily of fine-grained material will require a longer shaking period than a coarse-grained sample of equal weight. Sandy soil is always characterized by a very grainy texture and it doesn't mold when dampened. In soil analysis, there are six processes which are soil sampling technique, determination of texture of soil, determination of water content, determination of organic matter, determination of air content and soil pH. Soil texture Soil texture (such as loam, sandy loam or clay) refers to the proportion of sand, silt and clay sized particles that make up the mineral fraction of the soil. This chart is based on the USDA soil texture triangle, which provides an even higher level of detail when it comes to classifying soil texture. Particle Size Analysis for Soil Texture Determination (Hydrometer Method) Active In use from 2008-07-01 Abstract. Using a ruler, measure and record the height of each layer, and the total height of all three layers. CSIRO Publishing: Victoria. The relative percentages of these components present make up the soil’s texture. Complete particle size distribution curves. Texture is an important soil characteristic that is routinely determined in many soils-related studies. This method quantitatively determines the physical proportions of three sizes of primary soil particles as determined by their settling rates in an aqueous solution using a hydrometer. Move your finger up the line running parallel with the right side of the triangle. Andrew Jeffers, ©2018, Clemson Extension. What you see is what you get. Mark the top of the next settled layer with the permanent marker. Sandy soils are called coarse-textured, and clay-rich soils are called fine-textured. Soil texture analyses by hydrometer: modifications of the Bouyoucos method. Texture influences the ease with which soil can be worked, the amount of water and air it holds, and the rate at which water can enter and move through soil. Soil texture affects the movement and availability of air, nutrients and water in a soil (Hunt and Gilkes, 1992… Soil texture has agricultural applications such as determining crop suitability and to predict the response of the soil to environmental and management conditions such as drought or calcium (lime) requirements. The three major groups of soil particles are sand, silt and clay. (2)Department of Sustainable Agriculture Sciences, Rothamsted Research, Harpenden, United Kingdom. Standard curve for Fe on an AAS 8. Texture indicates the relative content of particles of various sizes, such as sand, silt and clay in the soil. Leave the jar on a level spot for 48 hours. Standard curve for Cu on an AAS 7. Soil texture can be determined using qualitative methods such as texture by feel, and quantitative methods such as the hydrometer method. Follow all directions, precautions and restrictions that are listed. Texture is important to overall soil and plant health as it relates to soil porosity, which refers to the pore spaces where air and water reside. Classifying a soil texture. The University of Western Australia: Nedlands, WA. […] This method is designed to secure complete dispersion of soil material below 2 mm. Soil Texture Analysis is done by determining the percentage of sand, silt and clay in a given soil. This is because of the impact that different soil texture characteristics can have on your ability to grow certain plants. 5. For example, sodic soils have a heavier field texture than is suggested by the laboratory determined PSA. The laboratory instructor will provide the percent moisture of the air-dry soil samples. Soil Texture Calculator. b. Using soil texture in the field Once the soil texture is determined in the field, general characteristics of a soil can be predicted with reasonable accuracy, which helps identify proper management practices to use. Soils with a higher proportion of sand retain less nutrients and water compared to clay soils. V.- WVU Extension Soil Sampling and Testing in Pasture. Comprise quartz and resistant primary minerals such as mica. The ideal soil texture is a mix of sand, silt, and clay particles, known as a loam. 1. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. The actual size of particles extends hugely over 4-orders of magnitude and significantly influences water holding capacity, plasticity, nutrient storage and microbial colonization. up to 100%. Jar filled a ⅓ of the way full with soil. NLWRA (2001) Australian Agricultural Assessment 2001. Texture analysis is – as it is commonly known – the basic and most often conducted soil analysis. 2. Andrew “Drew” Jeffers, ©2018, Clemson Extension. Standard curve for K on flame photometer 5. A 10-minute shaking period is suggested in Sieve analysis of soil procedure. CSIRO Publishing: Collingwood, Victoria. Meaning of Mechanical Analysis 2. McKenzie N, Coughlan K and Cresswell H (2002) Soil Physical Measurement and Interpretation For Land Evaluation. CSIRO Publishing: Collingwood, Victoria. Clemson University Cooperative Extension Service offers its programs to people of all ages, regardless of race, color, gender, religion, national origin, disability, political beliefs, sexual orientation, gender identity, marital or family status and is an equal opportunity employer. Some calculations are needed for this method including the use of a scaling factor for the pipette analysis and a calculation for the sieve analysis. You can learn simple DIY soil texture testing techniques here. Cien. Key points. A coarse-textured soil … The three primary soil particles are sand, silt, and clay. This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. For example, light soil refers to a soil high in sand relative to clay, while heavy soils are made up largely of clay. Natural soils are comprised of soil particles of varying sizes. Texture is an important soil characteristic because it will partly determine water intake rates (absorption), water storage in the soil, … Skip hours of tedious manual measurements, and focus on your research. Soil texture analysis is the measurement of the proportions of the various sizes of the soil particles. Soil data from a range of projects conducted across the state is constantly added to the soils database managed by the Department of Agriculture and Food, Western Australia. Soil texture is based on the USDA textural triangle. These size fractions are the mineral component of a soil and together determine soil texture. Process of Mechanical Analysis 3. Soil textures are classified by the fractions of each soil separate (sand, silt, and clay) present in a soil. Hunt N and Gilkes R (1992) Farm Monitoring Handbook. Texture is important to overall soil and plant health as it relates to soil porosity, which refers to the pore spaces where air and water reside. Add 1 tablespoon of powdered dishwashing detergent. You want to get percentages of sand, silt and clay . Soil texture analysis revisited: Removal of organic matter matters more than ever. For example, light soil refers to a soil high in sand relative to clay, while heavy soils are made up largely of clay. Copyright © 2020 Clemson UniversityClemson Cooperative Extension | 103 Barre Hall Clemson, SC 29634864-986-4310 | Contact UsHGIC@clemson.edu, College of Agriculture, Forestry and Life Sciences, Centipedegrass Yearly Maintenance Program, 1 tablespoon of powdered dishwashing detergent. Andrew "Drew" Jeffers, Spartanburg Cooperative Extension, Horticulture and Natural Resource Agent, Clemson University. It’s important to realize that only a tiny portion of a field is actually analyzed in the laboratory. For your soil texture calculations just ignore this. The first step in soil analysis is soil sample collection. 11. Large particles are known to settle out of suspension more rapidly than do small particles. Yes, there is a major relationship between the texture and constancy. Authors: Katharine Brown ( The University of Western Australia) and Andrew Wherrett (Department of Agriculture and Food, Western Australia). Soil texture is a dynamic feature of all soils and varies widely across soil series, soil orders and landscape. Jar showing the silt layer. A large quantity sample required longer shaking than a smaller sample. ADVERTISEMENTS: After reading this article you will learn about:- 1. The properties of each soil when doing this determines texture. Standard curve for Zn on an AAS 6. Soil Texture and Soil Structure. National Land and Water Resources Audit. Bouyoucos (1936) proposed a more rapid and simpler procedure called the hydrometer method. In soil analysis reports phosphor is usually indicated in mg/kg. If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988. Andrew “Drew” Jeffers, ©2018, Clemson Extension. Soil is a medium comprised of soil particles, organic matter, water, air and living organisms, all of which are important to the overall health of the soil and the plants that grow in it. A fourth term, loam, is used to describe equal properties of sand, silt, and clay in a soil sample. Jerah Frye & Sheryl Gill Soil Texture Analysis using a hydrometer PSA is a laboratory alternative to field texturing (see Measuring Soil Texture in the Field fact sheet) and offers a more reliable determination of particle size distribution. After sampling, another 56 h are required for the final report and the laboratory procedure employs hydrogen peroxide and sodium hydroxide as chemical dispersion agents. Andrew “Drew” Jeffers, ©2018, Clemson Extension. Soil texture is one of the most common features used by scientists and laymen to describe soils. 12. Soil analyses are related to potential nutrient uptake, supplementation of plant nutrients through fertilisation and the target yield. This is always the case that the first two sizes chosen will lead you to the third. This is the silt layer. Principles 4. How to determine Soil Texture: Soil texture is a very important soil property. Coarse textured soils are not sticky when wet and are easy to plow, hence the term light soil texture was coined. Soil texture (such as loam, sandy loam or clay) refers to the proportion of sand, silt and clay sized particles that make up the mineral fraction of the soil. The most common method for determining soil texture is the hydrometer method. Soil texture influences nutrient retention, water storage and drainage. Fill the jar ⅓ full of the soil to be tested, Jar filled with water, leaving space at top. Soil texture refers to the proportion of sand, silt, and clay in a soil. Three type of soil samples are used in soil analysis, which are housing area, pond and farm. Loamy soil – this is the soil we can only hope to achieve, as it’s considered the ideal soil type and texture. The ideal soil texture is a mix of sand, silt, and clay particles, known as a loam. Leave the jar in a level spot for 2 hours. The hydrometer measures the specific gravity of the soil suspension at the center of its bulb. 8. Analysis for soil nitrate­N, however,is done routinely only for a few selected crops,and it is used to refine their N­fertilizer recommendations.Soil samples can be analyzed for nitrate­Nif requested for other crops, but fertilizer­N Soil Texture Calculator Application: GET STARTED. The soil texture or textural class, as described here, is the same as the soil texture mentioned in Soils - Part 1: The Origin and Development of Soil. mate soil texture by feel fairly accurately with practice. Position your finger along the base line at the 50% mark. Determine the oven-dry weight of the soil sample. Use the soil texture analysis worksheet below to record results. Use the soil texture triangle to estimate the soil type for the site. 10. The textural triangle: It is used to determine the soil textural name after the percentages of sand, silt, and clay are determined from a laboratory analysis. “sandy clay” or “silty clay”. For a complete method, refer to Bowman and Hutka (2002). Hydrometer method is used to determine the particle size distribution of fine-grained soils passing 75 µ sieve. In addition to our soil nutrient testing, we also offer soil texture analysis (sand, silt, clay ratios), soil carbon and CO2 burst tests, which measures the CO2 respiration and is a proxy for the level of biological activity. A procedure for mechanical soil analysis, based on the most satis- factory of several methods of soil dispersion investigated, is here outlined. You can not change it, but understanding something about it will suggest ways to work well with it. Author information: (1)Department of Agroecology, Aarhus University, Tjele, Denmark. Pre-treatment of the soil may be needed to remove organic matter and salts such as gypsum. After dispersion, the amount of each particle group (sand, silt, clay) are determined by using a hydrometer (see picture). Soil texture influences nutrient retention, water storage and drainage. Andrew “Drew” Jeffers, ©2018, Clemson Extension, Jar showing the coarse sand layer settled at the bottom of the jar. All recommendations are for South Carolina conditions and may not apply to other areas. SOIL TEXTURE ANALYSIS “THE JAR TEST” Factsheet | HGIC 1656 | Updated: Feb 11, 2019 Soil is a medium comprised of soil particles, organic matter, water, air and living organisms, all of which are important to the overall health of the soil and the plants that grow in it. Place a mark the outside of the jar, showing the coarse sand layer settled at the bottom of the jar. Soil sampling for analysis. TOTAL HEIGHT OF LAYERS ________inches / cm, % SAND=(sand height)/(total height) x 100 =___________ % SAND, % SILT=(silt height)/(total height) x 100 =____________ % SILT, % CLAY=(clay height)/(total height) x 100 =____________ % SILT. Information regarding soil texture is also in the analysis because soil texture (sand, silt, and clay content) is a determinant of base WHC due to grain size packing, so it may be a control on observed changes with biochar (Liu et al., 2017). The ideal soil texture is a mix of sand, silt, and clay particles, known as a loam. Andrew “Drew” Jeffers, ©2018, Clemson Extension, 4. Other articles where Soil texture is discussed: soil: Grain size and porosity: Soil texture refers to the relative proportions of sand, silt, and clay particle sizes, irrespective of chemical or mineralogical composition (see the figure). Agr. Figure 1: Characteristic soils of the agricultural region of south-western Australia. Soils breakdown into 3 groups – clays, loams and sands. Soil test may refer to one or more of a wide variety of soil analysis conducted for one of several possible reasons. This simple approach to determining texture will not work if the soil contains a lot of gypsum. You will be able to estimate the soil texture during the sampling process. The sand percentage is on the right side, with lines extending upwardly, diagonally right to left (see blue line). However, unless you have access to professional soil analysis equipment, this level of detail is beyond what is needed for the average gardener. Inv. It's not too intimidating but it … Of course you can get a lab to test for you but getting up close and personal with your soil is never a bad thing. This is the clay layer that has settled on top of the silt layer. in diameter after organic matter and PSA is a reliable, reproducible technique that eliminates factors that may affect field texture such as organic matter content, clay mineralogy, cation composition and the presence of cementing agents (Bowman and Hutka, 2002). 9. The soil texture representation with the standard textural fraction triplet 'sand-silt-clay' is commonly used to estimate soil properties. In Soil Physical Measurement and Interpretation for Land Evaluation Those findings are plugged into a texture analysis triangle (see chart below) to determine soil classification. Texture is an important characteristic of soil and affects water holding capacity, drainage properties, root development and more. Soil is analysed to determine its ability to supply the necessary plant nutrients to the crop concerned. It is best to start at the base with the sand. The level and degree of soil heterogeneity may, to some extent, hinge on soil texture, given that soil texture is associated with the distribution of pores of different morphologies and also the locality of chemicals due to surface adsorption of mineral particles (Lilly and Lin, 2004; Plante et … Before you can describe the soil texture you need to know the relative proportions of sand, silt and clay within a soil sample. Lines corresponding to clay percentages extend from the percentages reading left to right (see red line). Your soil texture is an intrinsic part of your soil. SCOPE 1.1 This manual describes the procedure used by the Geotechnical Engineering Bureau to determine the distribution of fine-grained particle sizes of soil. If you’re lucky enough to have loamy soil , then you will notice clear water with a layered sediment on the bottom, with the finest particles on the top. Results are reported as percentages of the mineral fraction, % sand, % silt, and % clay. Soil testing and soil analysis gives the background knowledge on the chemical, physical and biological status of a soil that we need in order to properly manage our soils and crops. Particles greater than 2 mm are removed before analysis. = Air-dry wt./(1 + decimal of % H 2 O) b. This video will show you a way to measure the amount of sand, silt and clay in your soil, and then help you figure out your soil type. Contents:Soil Particle Size Distribution by […] SOIL TEXTURE DETERMINATION (HYDROMETER METHOD) The settling rates of dispersed particles in water are measured. Soil texture and soil structure are both unique properties of the soil that will have a profound effect on the behavior of soils, such as water holding capacity, nutrient retention and supply, drainage, and nutrient leaching.. Set on a level surface and time for one minute. Soil pH, Cation Exchange Capacity, organic matter and soil texture all have an impact on how we manage our soils and crops. Classifications are typically named for the primary constituent particle size or a combination of the most abundant particles sizes, e.g. Biological analysis Once the water clears take your measurements. The soil textural triangle is used to determine soil type based on sand, silt and clay percentages. Conclusion of Soil Analysis. Calculations: a. Laboratory analysis of soil texture is laborious and not environmentally friendly. In particular soil texture influences nutrient retention, water storage and drainage. Figure 1, taken from McArthur (1991), shows the soil types characteristic of south-western Australia. Introduction The soil, also referred to as the pedosphere, is a natural formation of the upper layer of the earth crust, formed from weathered rock as a result of the effect of various factors changing over time (climate, biosphere, hydrosphere, relief, and human activity). Texture refers to the relative abundance, by weight, of the size fractions – sand, silt, and clay. Texture is an important factor when determining the P-requirement. use the diagram for textural triangle (Figure 6) to determine the textural class of the soil. Trace your finger along the 80% sand line while simultaneously tracing another finger along the 5% silt line until the two meet.