For example, during a vegetation survey, the description of the soil together with a plant specimen will give some idea of the plant's environment and. In the field, the soil profile is divided into layers (horizons) based on one or more of the main properties. The depth of the soil profile can vary from a few centimeters (cm) - in the case of a thin soil over bedrock - to several meters.
The soil profile should be examined from the surface to a depth between 80 cm and 150 cm to adequately describe the soil for most. If encountered, it is important to describe some elements of parent material origin (eg granite, sedimentary) in addition to describing soil properties (Figure 6). Soil structure can be identified by laboratory analysis of the range of particle sizes present in the mineral fraction of the soil, and in the field by "soil texturing".
Field texture identifies how the soil feels, reacts and sounds when a small handful of soil is moistened and kneaded into a ball (or bolus) that is affected by the proportions of sand, silt and clay that make up the soil. However - and confusingly for those new to soil description - the terms sand, silt and clay, along with the term 'loam', are also used to describe the overall textural group of the described layer. The composition of the soil material, including the organic matter and different particle size fractions - the proportion of sand, silt or clay particles you estimate from a sample - largely determines the degree of texture.
Depending on the requirements of the soil descriptor, soil texture can be assigned to the three textural groups, or to the 11 textural qualities, or to the more defined national soil texture standards described in The Australian soil and land survey handbook, the yellow book (National Committee on Soil and Terrain [NCST] 2009).
Soil field texture guide
Before you start
Hand texturing
Take a small handful of soil (about the size of an egg) that will fit comfortably in the palm of your
Gently press out the soil between your thumb and index finger to form a hanging ribbon. The
The importance of the change in structure through the soil profile is reflected in soil classifications around the world. When the terrain soil texture remains within one textural group throughout the described profile—for example, sandy loam at the surface that becomes heavy loam at depth—the soil texture profile is called a uniform soil. Duplex soil has a textural contrast where there is a significant increase in soil texture (becoming more clayey) over a short vertical distance – sharply or suddenly.
Coarse soil particles are particles larger than 2 mm and are generally assessed by sieving the soil sample to separate them from the fine soil. Significant amounts of coarse fragments can affect soil properties, such as the effective rooting volume and the amount of plant-available water in the profile. To determine the color, hold an unformed, moist soil sample against the colors on the chart to find the best match (shown circled in Figure 19).
For example, you could describe the color of a speckled soil profile as yellow with red speckles (Figure 22) or gray with light yellow speckles (Figure 23). Soil pH is a measure of how acidic or basic (alkaline) the solute in the soil (soil water) is, and is a function of the concentration of hydrogen ions (H+) in the solution. Most plants like the soil solution to be close to neutral, although a pH range between 6 and 8 is usually fine.
Green in the upper left of Figure 24 indicates neutral to slightly acidic pH in the A horizon; purple colors indicate that the rest of the layers in the soil profile are alkaline. Soil salinity refers to soils that have a high concentration of soluble salts in the soil. Because sand particles will not hold as much salt from soil water as clay, the same salt level will affect plants more severely in lighter-textured soils (sand) than in heavier-textured soils (clay). .
The presence of lime (calcium carbonate) in the soil profile has significant implications for the efficacy of some chemicals applied to plants and soil, and has implications for laboratory testing of soil samples. The lime particles may be variable, including distinctly white or gray nodules and rock fragments, or finely distributed and otherwise indistinguishable from the soil (Figure 27). The presence of lime is detected by visible effervescence (effervescence) when drops of weak hydrochloric acid (1 molar HCl) are applied to soil or coarse fragments.
Soil structure for pedal soils is a complex area of soil description and is often not included in simple soil descriptions. It is often difficult to tell if the soil is saturated with water when examining the soil during a dry spell.
Other important soil-related properties
The presence of surface soil against water can be identified by gently placing a drop of water on the dry soil surface with a squeeze bottle or eye dropper. If the soil is repulsive, the drop will form a bead and settle on the surface of the soil or just penetrate the soil slowly. The degree of water resistance is accurately tested using water-ethanol solutions of different concentrations.
However, for simple soil descriptions it is sufficient to record the presence or absence of water repellency.
Other important land-related properties
Soil types and classification
Soils with a lot of ironstone gravel or boulders within 15cm of the surface, and ironstone gravel is a dominant feature of the profile Soils are consistently stony or stony (>50% . stones or rocks, but not ironstone boulders). Rocky or stony soil Level 2: Soil supergroups based on key profile characteristics up to 80cm For an extended classification beyond soil supergroups, refer to 'Soil groups of Western Australia' (Schoknecht & Pathan 2013). Soils with a sandy topsoil grading 80 cm to loamy or clayey subsoil (rock may occur at this depth).
Using this additional information, this profile would be classified as an alkaline gray shallow sandy duplex (WA Soil Group 402). Using this additional information, this profile would be classified as Duplex Sandy Gravel (WA Soil Group 302). Using this additional information, this profile would be classified as a wet saline soil (WA Soil Group 101).
With this additional information, this profile would be classified as Red Sandy Soil (WA Soil Group 463).
Glossary
Rock: the solid mineral material that forms part of the earth's surface; exposed on the surface or underground. Sand: a loose granular substance typically formed by the erosion of siliceous and other rocks and contributing to a major component of beaches, riverbeds, seabeds and deserts; the soil particle size is 0.02 to 2 mm. Clipping (related to soil texture): Slide your thumb across the soil to press out a band.
Silt: Sedimentary material composed of grains or disintegrated rock particles smaller than sand and larger than clay; the size of soil particles is 0.002 to 0.02 mm. Subsoil: the layer of soil below the soil surface, generally below 10 cm, and usually lower in organic matter and generally higher in clay content than topsoil. Texture group: soil groups separated by their particle size; three major textural groups are sand, clay, and silt.
Topsoil: surface layer of soil that is usually higher in organic matter and lower in clay content than the subsoil.
Resources related to this guide
Future topics include soil biology, soil compaction, soil water repellency, sodic and alkaline soils, nutrient management, and gravelly soils. If you have any questions or comments please email [email protected]. Please send your site cards or data to [email protected] for possible addition to the WA Profiles dataset to help improve state datasets.
Layer Layer name Layer depth Texture (Texture group or . grade) Boundary difference Soil water status.
