Soil: Structure, Texture, Bulk Density, and Soil Temperature

Soil: Structure, Texture, Bulk Density, and Soil Temperature

Soil Structure

The organization of soil particles into tiny clusters, known as peds or aggregates, is known as soil structure. Peds are formed when soil particles (including sand, silt, clay, and even organic materials) come together. The shape of the ped is determined by its makeup and the environmental factors that influenced its formation, including foot traffic, farming, freezing and thawing cycles, and wetting and drying out. They may be single-grained, blocky, columnar, platy, huge, or granular (like gardening soil or modelling clay) (like beach sand). The relationship between the soil’s structure and its pore space affects root development and air and water movement

Aggregates formed from soil particles and the pore space surrounding them make up the structure.


Both natural and man-made aggregates are possible (e.g., by tillage in wet soils; these aggregates are called clods)

The resilience of an aggregate to climatic changes, wind, and human activity like tillage. This is essential for gas exchange, root growth, and long-term resistance to wind and water erosion. It also serves as a measure of the soil’s health.

What causes aggregates in the soil to form?

i. Biological elements contribute to the cohesiveness of soil particles.

a) Exudates and root activity (sugars that act as glue)

b) Hyphae of fungi

c) Macrofauna activity, particularly trash and earthworms

d) Contains a lot of organic stuff

ii. Aggregates do not form well in the sand- and silt-rich soils. The kind and the number of clay particles have a significant impact on how well aggregates form and how long they last, While other types of clay produce weak aggregates, some types of clay produce very stable aggregates.

iii. Calcium can aid in soil stabilization, but gardeners must be mindful of the right kind to apply based on soil pH and the potential to increase salt. Gypsum is an affordable, non-toxic source of calcium overall, but it should be utilized carefully.

iv. The production of soil aggregates can be influenced by the climate, particularly the local temperature and precipitation. Particles have a higher chance of adhering together due to the physical process of freezing and thawing. The effect of rains as well as soil drying can separate particles.


The gaps in between soil or aggregate aggregates are called pores. They are essential for allowing water and air to permeate the soil and be stored there. Roots, large-scale creatures, and the majority of small ones cannot survive without air.

A) Pore types include

i. Interstitial pores: Tiny openings in the soil or aggregates.

ii. Animals or roots can create tubular pores.

b) Pore sizes: There isn’t a set size difference between the two size categories that pores are often divided into.

i. Macropores: Permit water and air to flow freely.

ii. Water can only travel through capillary flow and air movement through micropores is severely inhibited.

Soil Color

Soil mineralogy, which reveals what is in a particular soil, has a major impact on soil color. Deep orange to yellowish-brown to brown is the color of iron-rich soils. Dark brown or black is the color of soils with a high content of organic matter. A soil’s color can also indicate how it “behaves,” for example, a brightly colored soil that drains effectively would conduct a mottled pattern of greys, reds, and yellows, whereas a soggy, frequently wet soil will have a more muted appearance.

Bulk Density

To determine the amount of pore space in the soil, the bulk density of the soil is calculated by dividing the weight of a certain volume of oven-dried soil by the volume. The health of the soil is shown by it.

Factors that affect bulk density

i. The various mineral types that make up the soil’s constituent parts: Different minerals have different densities

 ii. soil structure Compared to silts and sands, clays are lighter.

iii. Content of organic matter: Comparing organic matter to mineral particles, organic matter has a lower bulk density. soil compactness The bulk densities of compacted soils are higher than those of uncompacted soils.

How bulk density informs cropping

High bulk density suggests soils that are compacted and limit root growth. These soils must be enhanced utilizing techniques including cover cropping, crop residue incorporation, and the use of crops with different rooting depths to boost the amount of organic matter.

Natural substance

Animal and microbial waste products at various stages of decomposition, dead plants, animals, bacteria, and fungus, or their parts, are all considered to constitute organic matter. At some point, all of these decompose into humus, which is comparatively stable in the soil.

Types of Biological Material

Organic matter’s significance Although organic matter only makes up a small portion of the soil, it has a significant influence on several variables.

The climate of the soil

Growers consider soil temperature to be significant, particularly for planting in the spring. A particular minimum temperature is required for the germination of many seeds.

The variables affecting soil temperature

Regional weather: The relationship between air and soil temperatures is very strong.

The steepness of the slope: In the Northern Hemisphere, aspects that face north are often cooler than those that face south. When the relative humidity is lower and the slope is steeper, the effect is more pronounced.

Topography: Microclimates are significantly impacted by topography. For instance, chilly air settles in low areas of valleys after flowing along drainages from mountaintops. These drainages and low places’ air and soil temperatures may be lower than those of the elevated areas nearby. The “citrus belt” in the San Joaquin Valley is a prime example of this.

Cover: Plants cover the earth, which lowers the temperature. Furthermore, through transpiration, growing plants lower the temperature of the air around them.

Soil color: Darker-colored soils are better at absorbing heat than lighter-colored soils.

Agricultural methods: Mulching can operate as an insulator, trapping heat in cold weather, and reducing heat by reducing insolation—the absorption of heat when it’s sunny.

The soil’s temperature affects its characteristics.

Biological activity: Reduced temperatures result in lower biological activity. There is not much biological activity below about 40°F.

Organic matter accumulation: Higher organic matter accumulation at lower temperatures.

Deterioration of the parent materials: Temperature changes facilitate the physical breakdown of rock and mineral grains (the rock part of sand, silt, and clay). Higher rates of chemical weathering result from warmer temperatures.

Availability of nutrients: Phosphorus, in particular, is scarce or difficult to get at low temperatures. As a result of the limited biological activity at certain temperatures, this is largely relevant.

Soil Texture

Sand, silt, and clay are the three types of soil-forming particles that are separated based on size. The biggest and smallest particles are made of clay and sand, respectively. A mixture of the three makes up the majority of soils. What gives soil its texture are the proportions of sand, silt, and clay. For instance, clay loam soil includes almost equal amounts of sand, sand, and clay.

Sand: 2.0 to 0.05 mm

Silt, from 0.05 to 0.002 mm

Clay Under 0.002 mm

The size classes of the soil’s mineral particles are as follows:


Sand is single-grained and loosely packed. The individual grains are easily distinguishable by sight and touch. As dried and squeezed in the hand, it will crumble when the pressure is released. When squeezed when damp, it will create a cast (a mass that holds together), but it will collapse when touched.


Loamy sand is single-grained and loose when it is completely dry. It is grippy, doesn’t ribbon, and isn’t sticky when wet, however, it might have very light clay stains. When squeezed when damp, it forms a cast that, even after very careful handling, does not break. Sand grains can be easily seen or felt as individual particles.


The silt and up to 20% clay in a sandy loam soil, which has a sand content of 45–85%, help to give it some coherence and prevent the formation of weak aggregates. One can see and feel the individual grains of sand. When it is liquid, however, it forms a cast that may withstand gentle treatment without shattering when squeezed or dry. There will be finger stains. It causes water to become foggy when placed in it.


A soil called loam has a reasonably uniform distribution of various sand, silt, and clay grades. It has a pleasant, little gritty feel to it and is smooth, slightly sticky, and slightly plastic-like. Dry aggregates are somewhat difficult to break. It will harden into a cast when wet that can be handled without breaking. My fingers are stained. When put in water, it causes the water to become foggy.


Silt loam is a type of soil that contains more than half silt-sized particles, moderate levels of fine sand, and less than 27 percent clay. Aggregates are tough to break when dry. It makes a solid ball and ribbons reasonably nicely when moist. It will create casts, dry or wet, that is easily handled without breaking. SILT Silt is a unique textural class that is difficult to locate in the natural world. Silt has a very soft, floury feel when it is dry. It has a greasy texture when damp but is neither sticky nor plastic.


Sandy clay loam is a type of soil that has between 45 and 80 percent sand, 20 and 35 percent clay, and 0 to 28 percent silt. Dry aggregates are brittle and difficult to break. It can be pinched into a ribbon when damp, creates a solid ball, and might reveal a fingerprint. It is plastic and sticky; it discolors fingers and makes the water murky.


Clay loam is soil with a somewhat fine texture that typically crumbles into aggregates or lumps that are solid or friable when wet and hard when dry. The dirt forms a cast that can withstand a lot of handling, ribbons well when moist, and exhibits a good fingerprint. It is also sticky and plastic. My fingers are stained.


When moist, a silty clay loam is plastic, sticky, and handles similarly to silt loam. Additionally, the soil forms a cast that can withstand decent handling when moist and, like clay loam, exhibits a good fingerprint. My fingers are stained. Pulverized earth has a floury texture.


It is extremely difficult to break aggregates when it is dry; tremendous pressure is required. It exhibits a nice fingerprint, is sticky or extremely sticky, moist, and plastic; it ribbons well and stains fingers.


A fine-textured soil containing 40–60% silt, up to 20% sand, and 40–60% clay is referred to as silty clay soil. When crushed, it feels somewhat floury and is very hard when dry. When moist, it becomes extremely sticky and that also tends to crystallize into blocks or prisms that are quite hard or extremely hard. plastic-like, and readily accept fingerprints. It ribbons nicely, clouds water, and leaves stains on fingers while forming a cast that can withstand heavy handling.


 Clay is a soil with a fine texture that also tends to crystallize into blocks or prisms that are quite hard or extremely hard. When damp, it becomes highly sticky and plastic, ribbons beautifully, and makes an excellent fingerprint. When damp, some clays become highly rigid or very rigid.

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