FACTORS AFFECTING SOIL PHYSICAL PROPERTIES.
The pressures that are exerted on soils have an impact on their physical characteristics. As was said in the section on soil texture, this physical characteristic cannot be changed quickly or inexpensively except by natural processes, which by cultural and agricultural standards would be disastrous.
On the other hand, both natural, and non-catastrophic processes and soil management methods have the potential to change soil structure. The following are the ones having the most impact.
Content of Organic Material
A soil’s organic matter content may go up or down depending on how it is handled. Manure may be added, or green manure crops can be grown and plowed in to augment it. Tillage may help reduce it.
This transformation occurs naturally over a lengthy period of time when soil organic matter rises as a result of the buildup of leftovers from deceased plants and animals.
When manure or green manure is introduced, the amount of fresh residue or “recently deceased” organic matter rises. As a result, there are more living things since there is more food available. These activities lead to a steady increase in the relatively stable humus component of soil organic matter.
organisms in soil
If there is enough food, water, and air available, soil organisms will construct a structure even in unstructured or poorly structured soils. Individual soil particles are bound together by soil organisms to form structures.
The majority of soil bacteria produce an exudate that sticks to the outside of their cell walls. This gives them the ability to “glue” themselves to other soil particles and to soil particles themselves, preventing them from being transported through the soil profile by water evaporating from the soil.
Two nearby soil particles are “glued” together as a result of this secondary action by bacterial clumps.
Another factor that holds particles together is microbial development in the soil. Mycelia are threadlike structures that fungi spread across the earth. These link different particles together like a little root system.
Additionally, they connect unique peds to one another, strengthening the framework. The bigger species, such as earthworms and arthropods, create major channels and pores in the soil.
Organic and inorganic soil particles with extremely tiny sizes and a high surface area to mass ratio are called soil colloids.
Water and colloids both have a weak electrical charge. As the water in the soil evaporates, the colloids are attracted to the bigger particles and each other by the soil water that has bound to them. Colloids and bigger particles are clustered via this mechanism. These particles are drawn together form an aggregate by ongoing evaporation.
Tillage may affect soil structure both favorably and unfavorably.
Soil organisms will construct a sturdy structure very quickly when the soil has been adequately tilled and has enough of food and water. This will result in a favorable outcome. The structure will suffer from inappropriate tillage techniques and soil moisture levels that are too high or too low.
Thawing and Freezing
The effects of freezing and thawing on the soil exist. The soil particles and/or peds are forced apart when the liquid in the soil freezes and expands. This temporarily widens the pore spaces. The increased pore holes often persist when the soil moisture thaws, allowing the structure to open up.
You may have experienced this impact if you’ve ever crossed a field just after it just thawed. Walking on the ground seems soft, and as you dig deeper into the light dirt, your footsteps become more noticeable.
The quantity of pore space in the soil gradually recovers to about its previous level due to gravity, traffic-related compaction, and water flow through the soil.
There is a tiny beneficial impact even if freezing and thawing only momentarily expand the pore space in soil. The greater quantity of oxygen in the soil will help the soil organisms thrive and create a more stable structure if the correct circumstances are present during the portion of this transient expansion of pore space.
The physical characteristics of soil may be affected by water flow in two different ways: favorably or unfavorably. Water will travel vertically as it soaks into the soil. As a result, the soil pores are filled with water, some of which are stored for use by crops. The removal of minerals from the soil by the water as it permeates the soil is a drawback of this process.
Hydraulic slumping, a collapse of the soil structure that results in less pore space than before the tillage, may happen when water is flowing quickly through a soil that has recently been tilled.
The water flowing through the tillage zone of soils containing any amount of clay will take clay particles with it. Some of the clay will be deposited as it slows down near the base of this zone. A hard pan or tillage pan is the result of this. Similar to how clay dumped into a pond to protect the bottom does, this thin coating of clay prevents water flow.
Erosion often happens when water travels horizontally across soil. The water quickly descends through the tillage zone in a field with shallow tillage.
Water moves more slowly at the bottom of this zone because it can’t penetrate untilled soil as quickly. Water is compelled to go vertically in locations with any slope as it gathers there, carrying dirt along the way.
SOIL PHYSICAL PROPERTIES APPLICATIONS
Any agricultural system’s soil management strategies must be determined by an understanding of the physical characteristics of soils in general. From one field to the next and even within one field, soil types (and therefore textures) may differ greatly. The physical characteristics of the soil may also be impacted by management considerations.
Techniques for managing soil should change to reflect this. For instance, during tillage, sandy soil should have a greater moisture content than clay soil.
Identifying Soil Texture
The most crucial elements in creating a soil management plan are comprehending soil texture and recognizing the texture of the soil. A soil-testing facility can determine the soil texture. These tests might, however, be rather pricey.
The information at hand may be used to identify the textures of the soil. All county soil conservation offices have generalized soil type maps on hand. These aerial pictures of the county have soil borders overlaid on them.
They also provide a list of all represented soils and information on their typical texture.
Identification of Soil Structure
As opposed to texture, soil structure is more difficult to assess. That’s because management, the amount of organic matter, and soil biology are only a few of the variables that affect the structure.
The topsoil should be gently removed without compacting or tearing it up in order to reveal the soil structure. This may be examined visually and compared to soil pictures or other soils to show the various levels of structure.
CONCENTRATION OF HYDROGEN AND HYDROXYL – PH
The pH test was one of the first chemical analyses performed on soils. The relative concentrations of the ions hydrogen and hydroxyl (H+ & OH-) are measured by this assay. The soil is acidic on the pH scale when the concentration of hydrogen ions is high. The soil is basic when the amount of hydroxyl ions is significant.
A logarithmic scale is the foundation of the pH scale itself. The pH scale may be understood without having any prior knowledge of logarithms. The scale runs from 0 to 14, with 0 being entirely acidic and 14 being completely basic. On the scale, a neutral result is a 7, which is in the center.
Additionally, since this scale is logarithmic, a shift in one number indicates that the soil is 10 times more basic or acidic. For instance, if the number changes from 6 to 5, the soil is now 10 times more acidic.
With increased chemical use by crops, soil pH became crucial. The majority of the soil life was killed by salt fertilizers and pesticides, which prevented these creatures from naturally cycling nutrients.
The plant life turns to absorb the byproducts of chemical processes in the soil for nutrition when the soil life is repressed. The pH of the soil influences these processes in turn.
pH is less important in an organic management system when soil organic matter and soil organisms are adequately maintained. This is so that plants may easily get the plant nutrients that the soil life releases into the soil. Plants are less reliant on the byproducts of chemical processes as a result.
Similar to how a thermometer monitors body temperature, soil pH is a tool for identifying mineral shortages in the soil and imbalances in organic processes.
When we have a fever, we can tell that something is wrong because we are unwell but not sure why.
Similar circumstances apply to soil pH testing; we are aware of a mineral imbalance or deficit but are unsure of what it is.
Previously, pH solely served as a measure of relative acidity or alkalinity.
We have begun to utilize pH in a new manner as we have learned more about how the mineral content of soil affects soil quality and plant nutrition.
For example, we use pH to evaluate if further testing for certain minerals is required rather than using pH to decide how much lime to apply to acidic soil.
Sand, silt, and clay are the tiny mineral particles that are created as rock weathers into soil. Quartz (silicon dioxide) makes up the majority of sand and silt, although the makeup of clay particles varies depending on the parent rock.
Organic matter is composed of living things as well as extinct plant and animal life. Even though most soils only contain 5% or less organic matter, it is crucial to the soil’s fertility. In the pores between the soil’s solid particles, there is either air or water present. The quantity of water in the pore space will affect how much air is there.
The relative size of the particles that predominate in a given soil is used to categorize the texture of the soil. These include sand, silt, and clay, listed in order of greatest to smallest particle size. Loam, or soil with varying concentrations of sand, silt, and clay particles, is the fourth type.
The arrangement of the clay, silt, and sand particles into aggregates or peds determines the nature of the soil structure.
While soil structure cannot be readily modified, there are a variety of factors and management techniques that can. These include tillage, freezing and thawing, soil colloids, organic matter content, soil organisms, and water flow.
Understanding the soil structure and texture of the fields that will be farmed should serve as the foundation for soil management strategies. This data may be obtained via soil maps and an examination of a topsoil profile.
A soil’s acidity or alkalinity may be determined by its pH. Because the level of acidity affects the chemical processes that release the nutrients, pH is a crucial consideration when plants rely on chemical fertilizers for sustenance. In organic systems, pH is less important since soil life provides nutrients that plants may take up.