What is weathering in agriculture


Weathering describes the means by which soil, rocks and minerals are changed by physical and chemical processes into other soil components. Weathering. The means by which soil, rocks and minerals are changed by physical and chemical processes into other soil components.


What is weathering?

What is weathering? The wearing away or break down of rocks by agents present in the atmosphere like temperature, moisture and frost are known as weathering. Let us learn about the effects of weathering!

What are the main causes of biological weathering?

The most common forms of biological weathering result from the release of chelating compounds (such as certain organic acids and siderophores) and of carbon dioxide and organic acids by plants.

What are the most common solution weathering processes?

One of the most well-known solution weathering processes is carbonation, the process in which atmospheric carbon dioxide leads to solution weathering. Carbonation occurs on rocks which contain calcium carbonate, such as limestone and chalk.

What is the degree of weathering of soil?

The degree of weathering of a soil can be expressed as the chemical index of alteration, defined as 100 Al2O3/ (Al2O3 + CaO + Na2O + K2O). This varies from 47 for unweathered upper crust rock to 100 for fully weathered material.


What do you mean by weathering?

Weathering is the breaking down or dissolving of rocks and minerals on Earths surface. Once a rock has been broken down, a process called erosion transports the bits of rock and minerals away. Water, acids, salt, plants, animals, and changes in temperature are all agents of weathering and erosion.

What is weathering and its types?

Weathering is the breakdown of rocks at the Earth’s surface, by the action of rainwater, extremes of temperature, and biological activity. It does not involve the removal of rock material. There are three types of weathering, physical, chemical and biological.

What are the three types of weathering in agriculture?

Physical WeatheringExfoliation: When temperature of rocks rapidly changes that can expand or crack rocks. … Freeze-thaw: When water freezes, it expands. … Abrasion: When the wind blows, it can pick up sand and silt, and literally sandblast rocks into pieces.Root Expansion: Like freeze thaw, roots grow bigger every year.More items…

What is weathering and why is it important?

Weathering causes the disintegration of rock near the surface of the earth. Plant and animal life, atmosphere and water are the major causes of weathering. Weathering breaks down and loosens the surface minerals of rock so they can be transported away by agents of erosion such as water, wind and ice.

How do plants cause weathering?

Plants grow around rocks where roots penetrate and crack the rocks. Plants grow around rocks and disintegrate the rock into soil. Water from plants is absorbed by minerals in rock and they are weathered due to expansion and contraction. Plant roots cause temperature fluctuations within the rocks to cause weathering.

What are factors of weathering?

There are two factors that play in weathering, viz. Temperature and Precipitation. Warm climates affect by chemical weathering while cold climates affect by physical weathering (particularly by frost action). In either case the weathering is more pronounced with more moisture content.

What are the 4 main types of weathering?

There are four main types of weathering. These are freeze-thaw, onion skin (exfoliation), chemical and biological weathering.

What are 2 types of weathering?

The two main types of weathering are physical and chemical weathering. This page describes mechanical (physical) weathering (and more).

Why is weathering important in agriculture?

As soils weather, the dissolution of primary minerals forces plants to rely on recycling and atmospheric deposition of rock-derived nutrients. Thus, for many terrestrial ecosystems, weathering ultimately constrains primary production (carbon uptake) and decomposition (carbon loss).

Why is weathering important to soil?

Weathering breaks down and loosens the surface minerals of rock. Hence, the broken rocks are transported to another place where it decomposes and forms soil. Therefore weathering is important for soil formation.

Why is weathering important to the environment?

Weathering is a part of geomorphic processes leading to the disintegration and decomposition of rocks and minerals on the earth’s surface as a result of physical and chemical action that leads to the formation of soil being a most vital natural resource of rock weathering. Development of soils in an environment …

How does chemical weathering differ from physical weathering?

Chemical weathering differs from physical weathering because it doesn’t just weaken and break apart rock, it also changes the chemical makeup of rocks. For example, carbon dioxide and water combine to create carbonic acid, which can dissolve rocks like limestone.

What are the two agents of chemical weathering?

Two other agents of chemical weathering are rust and acid rain. Rust acts on rocks that contain iron through the process of oxidation. Rust weakens rocks and eventually they break.

How are rocks broken down?

Instead of using a chisel like a sculptor, rocks and minerals are broken down in many different ways through a process called weathering. From water and wind to plants and animals, the earth puts all types of rock through natural wear and tear. The pieces of broken rock are then carried away by erosion and are deposited in rivers, lakes, and oceans.

What is another term for erosion?

Weathering is another term for erosion. There are several types of erosion, wind, flowing water and freezing/thawing water. Let’s look at a few scenarios and determine what type of erosion it is.

Why do mountains have wind erosion?

Wind erosion predominately because of the dry desert where the Sphinx is located in Egypt. 4. Mountains usually have streams. Mountains with a lot of vegetation means constantly flowing streams due to plentiful rainfall.

Why do mountains have streams?

4. Mountains usually have streams. Mountains with a lot of vegetation means constantly flowing streams due to plentiful rainfall. The Appalachian mountains are far enough from the equator and have high enough elevation to have water freezing in cracks of rocks; the water expands when it freezes, pushing the rocks apart.

What causes rock to expand and contract?

Temperature. Over time, changes in temperature cause rock to repeatedly expand (grow bigger) and contract (grow smaller), which weakens them and leads to breakage. Deserts, in particular, have very high temperatures during the day and very low temperatures at night.

How does chemical weathering affect soil?

Chemical weathering results in an average net loss of 24 ± 4% of the soil mass at both sites, calculated as the average CDF soil, and CDF values are not significantly different at the two sites. Dahlgren et al. (1997) observed that clay content of the low elevation soils exceeds that of WB soils by a factor of two. This suggests a discrepancy in how soil weathering intensity is recorded by CDF and clay abundance. The CDF quantifies net elemental losses; however, secondary mineral formation is the balance between chemical dissolution of primary minerals and the leaching of weathering products. Potential mass loss may exceed net mass loss at low elevation, due to secondary mineral development and retention, in agreement with previous observations of the low leaching potential of clay minerals in these soils compared to high elevation soils ( Dahlgren et al., 1997 ). Thus, the total chemical alteration at BG site is greater despite similar net losses to WB.

Why do outcrops crop out?

But outcrops crop out because weathering and erosion have affected them differently than the bedrock that has been converted into soil. This may be due to spatial variability in weathering and erosion processes. It may also be due to variability in some intrinsic property of the rock. In that case, outcrops may be a poor chemical proxy for the parent material that has generated the soil. Ideally a few samples from great depth or a road cut, if available, should be taken to confirm that outcrops are similar to unweathered material at depth.

Why are soil samples needed?

Many samples of soil and saprolite are required to characterize weathering at the catchment scale. Samples must be taken from widely distributed surfaces and pits, to characterize spatial variability in bulk chemistry of weathered soil and saprolite ( Riebe et al., 2001b, 2003, 2004a ).

What are the effects of pH on soil?

(2010) investigated pH effects on soil colloidal P release from soil water extracts and concluded that colloid mobility was significantly enhanced at low (1.4–6.0) and high pH (9.9). With decreasing pH (6.0–1.4), total concentrations of colloidal Mn, Si, Al, Fe increased while their proportions decreased, indicating that dissolution of these minerals was the primary mechanism inducing the colloid release in soils under acidic pH. The colloidal P amount also turned out to be highly related to colloidal Al. Therefore, the authors argued that Al oxides were the predominant colloidal carriers for P within this pH range. Other colloidal forms like organic matter-bond P, Fe P, clay mineral bond-P were also observed. Under high pH (9.9), organic matter coatings were interrupted, also resulting in the colloid release, enhancing colloidal P movement. Furthermore, among several mineral colloid species, only colloidal Fe had an increase at high pH, indicating an important role of iron (oxyhydr)oxides. Its correlation with colloidal P amount supported such a role and colloidal Fe accounted for 50.3% of the variation in colloidal P.

How are soils formed?

Soils are formed from residual material or from material transported and deposited by water, wind, ice, or gravity. The productivity of residual soils is influenced by rock and mineral type and the rate at which they weather. Limestones and shales weather faster than most sandstones creating deeper, more fertile soils. Common igneous and metamorphic soil-forming rocks are generally more resistant to weathering, although most are rich in minerals required by plants. Soils derived from transported materials are generally very productive, as they are found in low landscape positions and consist of existing soil materials transported from higher elevations. The position, orientation, and layering of geologic materials also influences soil weathering rates, soil water movement and storage, and depth of rooting. In the northern hemisphere, steep, mid-slope positions with southwest aspects have the shallowest soils and highest evaporative demand. The deepest, most productive soils are found on northeast-facing slopes at slope bottoms. Topographic features influence productivity predominantly by controlling plant available water and controlling the harmful effects of fire, wind, snow, and ice. On flatter terrain, slight changes of only a few centimeters in elevation can influence the depth to a water table and the effective soil depth that trees can exploit. In the case of soils with high water table, productivity is more often nutrient limited due to insufficient aerated soil volume.

How do earthworms affect soil?

He pointed at the importance of earthworm activity for soil formation and weathering, and the role of earthworm casting (bioturbation) for soil fertility and plant growth. Nowadays, concern about the transport and bioavailability of heavy metals, radionuclides, and organic contaminants in soil is an important driver of research into bioturbation. It has been estimated that earthworms completely turn over the topsoil of grassland once in 5–20 years. Bioturbation was a major cause for the transport of polychlorinated biphenyls and PAHs in soil. Animal-mediated dispersal of bacteria in soil has also been observed. Earthworms transport surface-inoculated soil bacteria down to depths of 40 cm and were found to facilitate the transfer of plasmids between spatially separate bacterial species.

Does temperature affect soil moisture?

Of particular interest in evaluating the effect of temperature on soil processes is its effect on the viscosity of soil moisture. Infiltration rates and hence soil-moisture fluxes are known to increase significantly with increased temperature ( Shanan and Tadmor, 1979 ). Cumulative effects should be pedogenetically significant but an accurate evaluation of this effect in pedogenesis is still lacking. For several chronosequences in high latitudes, Bockheim (1980) obtained a significant positive correlation with mean annual temperature for such properties as depth of oxidation, solum thickness and B-horizon clay content; all of which could be attributed to better moisture infiltration.

What is the process of weathering?

Weathering processes are divided into physical and chemical weathering . Physical weathering involves the breakdown of rocks and soils through the mechanical effects of heat, water, ice, or other agents. Chemical weathering involves the chemical reaction of water, atmospheric gases, and biologically produced chemicals with rocks and soils.

How does chemical weathering work?

Chemical weathering takes place when water, oxygen, carbon dioxide, and other chemical substances react with rock to change its composition. These reactions convert some of the original primary minerals in the rock to secondary minerals, remove other substances as solutes, and leave the most stable minerals as a chemically unchanged resistate. In effect, chemical weathering changes the original set of minerals in the rock into a new set of minerals that is in closer equilibrium with surface conditions. However, true equilibrium is rarely reached, because weathering is a slow process, and leaching carries away solutes produced by weathering reactions before they can accumulate to equilibrium levels. This is particularly true in tropical environments.

How does frost wedging work?

When water freezes, its volume increases by 9.2%. This expansion can theoretically generate pressures greater that 200 megapascals (29,000 psi), though a more realistic upper limit is 14 megapascals (2,000 psi). This is still much greater than the tensile strength of granite, which is about 4 megapascals (580 psi). This makes frost wedging, in which pore water freezes and its volumetric expansion fractures the enclosing rock, appear to be a plausible mechanism for frost weathering. However, ice will simply expand out of a straight, open fracture before it can generate significant pressure. Thus frost wedging can only take place in small, tortuous fractures. The rock must also be almost completely saturated with water, or the ice will simply expand into the air spaces in the unsaturated rock without generating much pressure. These conditions are unusual enough that frost wedging is unlikely to be the dominant process of frost weathering. Frost wedging is most effective where there are daily cycles of melting and freezing of water-saturated rock, so it unlikely to be significant in the tropics, in polar regions, or in arid climates.

What is the chemical reaction of water, atmospheric gases, and biologically produced chemicals with rocks and soils?

Chemical weathering involves the chemical reaction of water, atmospheric gases, and biologically produced chemicals with rocks and soils. Water is the principal agent behind both physical and chemical weathering , though atmospheric oxygen and carbon dioxide and the activities of biological organisms are also important.

What is weathering in Jordan?

Weathering is the breaking down of rocks, soils, and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms . Weathering occurs in situ (on site, with little or no movement), …

Why is basalt weathered?

In tropical settings, it rapidly weathers to clay minerals, aluminium hydroxides, and titanium-enriched iron oxides. Because most basalt is relatively poor in potassium, the basalt weathers directly to potassium-poor montmorillonite, then to kaolinite. Where leaching is continuous and intense, as in rain forests, the final weathering product is bauxite, the principal ore of aluminium. Where rainfall is intense but seasonal, as in monsoon climates, the final weathering product is iron- and titanium-rich laterite. Conversion of kaolinite to bauxite occurs only with intense leaching, as ordinary river water is in equilibrium with kaolinite.

Why is carbonate dissolution important in glacial weathering?

Despite a slower reaction kinetics, this process is thermodynamically favored at low temperature, because colder water holds more dissolved carbon dioxide gas (due to the retrograde solubility of gases). Carbonate dissolution is therefore an important feature of glacial weathering.

How do wildfires affect the landscape?

Wildfires can be an important agent of landscape change when linked with sufficient rainfall. Decreased soil permeability following wildfire, coupled with removal of vegetation and litter, can result in lower interception and infiltration rates, and increased runoff. These changes may be accompanied by increased erosion through sheetwash, rilling, and dry ravel of granular soil and rock material, and increasing intensity and frequency of floods, debris flows, rockfall, and landslide movement. Studies have shown that the window of disturbance to the landscape caused by wildfire is typically on the order of 3–4 years, although some effects in some environments can persist up to 30 years or even longer in rare instances. Moreover, sedimentological records show that the incidence of wildfire increases during warmer climate periods.

How long does it take for soil to form?

It takes hundreds or even thousands of years for soil to develop, making it extremely difficult to measure soil formation processes over time. Time is required for the formation of soil, as it interacts with the other soil-forming processes. Despite its importance, two soils located at different regions may form at a completely different rate. For example, a soil in a warm climate with high rate of precipitation and high parent material permeability will form much more rapidly than that located in a cool and dry climate with a resistant parent material.

What are the effects of wildfires?

Primary effects of fire include removal of soil-mantling vegetation and litter, deposition of ash, creation or destruction of water-repellent soils, and physical weathering of boulders and rock.

What caused the Devonian cooling?

The Devonian cooling trend was driven by a sharp decline in the partial pressure of carbon dioxide in the atmosphere from the Givetian to the Early Carboniferous ( Figure 2), a decline driven by the establishment of extensive terrestrial land plant cover (discussed in the previous section) and associated soil weathering. Land plants themselves fixed atmospheric carbon in their tissues (see CARBON CYCLE ), and nutrient run-off produced by their activity on land triggered blooms of phytoplankton growth in the Devonian shallow seas. This, in turn, led to further atmospheric carbon fixing and organic carbon burial in extensive Middle and Late Devonian black-shale deposits. Chemical weathering of rocks by land plants also produced massive run-off of calcium and magnesium-rich minerals which precipitated as carbonates in the oceans, further drawing down the carbon dioxide partial pressure of the atmosphere.

How does fire affect landscape change?

Refining and expanding our understanding of fire as an agent of landscape change requires a consideration of current and past variability in the occurrence of fires. This variability may involve more than consideration of fire return periods for the vegetative communities present in a particular landscape. At the landscape scale, the temporal and areal occurrence of wildfires is not solely controlled by the character of the vegetative community being burned. It is also influenced by climatic shifts and anthropogenic changes. Consequently, understanding the influence of fire on the landscape will require careful evaluation of past and present wildfire regimes.

How do ecosystems change?

Ecosystems change through time (see Chapters 10 and 11Chapter 10Chapter 11). These changes may be gradual and subtle (the millennial losses of minerals from a weathering soil) or fast and dramatic (a fire sweeping through a forest). Both external forces (changes in climate or nutrient inputs) and internal dynamics (aging of a tree population, accumulation or depletion of materials in a soil or a lake) are important in driving temporal changes in ecosystems. In some cases, changes are directional and predictable (e.g., soil weathering, the filling of a lake basin), while in other cases changes may be idiosyncratic and difficult to predict (e.g., the arrival of an invasive species, disturbance by a hurricane). Understanding and predicting how ecosystems change through time is of great theoretical and practical interest, and is a major part of contemporary ecosystem science.


Weathering is a geological destructive process which leads to formation of simple compounds from solid rocks of earth crust. When these rocks are broken by chemical reactions occurring due to their exposure to water , oxygen, acids , carbon etc., it is termed as chemical weathering.

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