Unveiling the Composition and Properties of Soil

Soil is an essential component of nature that significantly influences various aspects of our lives. Its quality plays a crucial role in determining crop productivity, as well as the nutritional and taste value of the produce. The United States is known for its remarkable soil diversity, with each type exhibiting distinct physical and chemical properties.

What is the precise definition of soil?

Soil, in its traditional definition, serves as the natural medium for the growth of land plants. It covers the Earth's surface, except in areas of bare rock, perpetual frost, deep water, or glaciers, and in this context, soil can be characterized as a continuum, with its thickness determined by the depth at which plants can establish roots.

The term "soil" also refers to a natural body consisting of solids (minerals and organic matter), liquids, and gases. It occupies physical space on the land surface and exhibits distinctive horizons or layers, resulting from the accumulation, loss, transfer, and transformation of energy and matter. 

The properties of soil are influenced by the specific substances present in a given geographic location and the prevailing climate. As a result, soils in the United States exhibit diverse chemical and physical compositions. This diversity is of great significance across economic sectors like agriculture, forestry, construction, and environmental protection. Understanding the properties of different soil types is essential for effective land management practices.

Why is soil knowledge important?

Soil knowledge holds significant importance for various reasons. Primarily, the structure of soil plays a crucial role in agriculture by determining crop yields and the taste and nutritional value of the harvested produce. Therefore, studying the soil profile is a fundamental approach to assess the productive potential of an area before commencing development.

Moreover, understanding soil is essential for making effective management decisions in agriculture, forestry, and natural ecosystems. Knowledge of the chemical and physical composition of soil enables the use of appropriate fertilization methods, optimized crop planning, efficient water management, and implementation of soil protection practices to prevent erosion and degradation.

Additionally, soil knowledge is vital in infrastructure and construction planning. Conducting soil investigations prior to construction projects allows for assessing soil bearing capacity, ensuring structural stability, and anticipating potential issues related to settlement and changes in soil conditions.

Soil Properties

Soil properties encompass a set of characteristics that define its physical, chemical, biological, and mineral composition. These properties determine the fertility of the soil, which refers to its ability to support plant growth and development. We can distinguish primary or natural properties, which result from geological and climatic processes, and functional or secondary properties, which can be influenced by human practices such as cultivation, fertilization, and soil management.

Different types of soil can be identified based on their specific properties. For example, acidic soil is characterized by a high concentration of hydrogen ions, while alkaline soils have a high level of hydroxide ions. The soil pH (acidic, alkaline, or neutral) can be measured using appropriate devices.

One of the most important soil properties is its structure, which determines the ability of soil particles to aggregate into larger clumps known as aggregates. Soil structure influences its porosity, which is the sum of free spaces within a given volume of soil. Porosity, in turn, affects the soil's capacity for water and air movement, which is crucial for plant health.

Other significant soil properties include:

  • Soil colloids: The smallest soil particles that play an active role in chemical processes and determine soil fertility.
  • Soil density: It measures the mass of soil and indirectly indicates the amount of air in the soil.
  • Soil compactness: The strength with which soil particles are bound together.
  • Soil viscosity: The adherence of soil to different surfaces.
  • Sorption: The soil's ability to retain various substances on its surface.

Water, permeability, and thermal properties of soil are also essential. Soil water-holding capacity depends on its mechanical components, structure, and presence of colloids. Permeability defines the soil's ability to absorb and transmit water downward. Thermal property refers to the amount of heat required to raise the temperature of a given volume of soil by 1 degree Celsius.

What are soil organisms, and what is their role in the environment?

Soil organisms play a crucial role in soil cultivation and significantly impact its properties. They facilitate the conversion of organic matter into plant-available nutrients. These organisms encompass a wide range of life forms, including fungi, bacteria, viruses, and algae. They are often found in the vicinity of plant root systems and areas rich in organic matter or animal manure.

Other organisms like protists, nematodes, and small arthropods regulate the activities of the lower-level microorganisms. They contribute to maintaining balance within the soil ecosystem, with some acting as pests or plant parasites, while others act as activators of soil microflora.

Soil-dwelling creatures also include earthworms, termites, ants, isopods, millipedes, centipedes, beetles, caterpillars, and scorpions. Soil microorganisms are crucial for soil aeration, which enhances permeability. Through their biological activity, microorganisms create channels and spaces within the soil structure, promoting improved water flow. This availability of water benefits plants and other organisms residing in the soil.

Moreover, soil organisms enable proper plant development by contributing to the formation of humus, a soil layer rich in organic matter that is vital for maintaining soil fertility. The United States, with its 12 main soil types, exhibits a diversity of soil organisms, directly impacting agricultural possibilities across different regions of the country.

Acidic and alkaline soils – key differences

Acidic and alkaline soils differ in fundamental properties that directly impact land cultivation. The soil pH, which measures acidity or alkalinity, is one of the most important soil components. It determines soil properties, defines soil types, and influences plant nutrient uptake.

Acidic soils have a pH ranging from 3.5 to 5.5 and are characteristic of areas with high humus content but low calcium levels. The low pH affects soil structure, increases the risk of mold development, and can lead to a decline in beneficial soil bacteria. To determine soil pH, a test kit can be used to measure calcium content and prevent excessive liming. Soil samples can be obtained from any part of the cultivation area.

On the other hand, alkaline soil has a pH above 7.0 and contains high levels of calcium. Soils with alkaline pH tend to form a granular structure, resulting in improved water-air relationships. These soils contain alkaline cations such as Ca2+, Mg2+, and K+. However, the phosphorus availability is low in alkaline soils, which can hinder proper plant development. Alkaline soil pH is a result of an excess of hydroxide ions (OH-) over hydrogen ions (H+), which is typical for dry and semi-arid regions.

Soil pH is a variable value influenced by numerous factors, thus regular soil testing is recommended. It is important to remember that soil pH has a significant impact on the plant's ability to absorb nutrients, which is crucial for their proper development. The choice of soil type should depend on the preferences of the cultivated plants.

The importance of organic matter in determining soil fertility

Organic matter plays a crucial role in maintaining soil health and fertility. It is a fundamental indicator of soil quality, influencing its physicochemical properties such as sorption and buffering capacities. High levels of organic matter in soils stabilize their structure, reducing susceptibility to compaction and degradation caused by water and wind erosion.

Organic matter, primarily of plant origin, contains all the essential nutrients for plant growth, making accumulated organic matter a reservoir of nutrients. Furthermore, organic matter improves soil structure by maintaining its layers and minimizing erosion. Active and some resistant organic components of the soil, along with microorganisms like fungi, participate in binding soil particles into larger aggregates. The stable organic fraction, known as humus, absorbs and retains nutrients in a form readily available to plants. In practice, organic matter releases these nutrients upon decomposition, thereby replenishing the nutrient supply for plants.

Moreover, organic matter improves soil structure by maintaining its layers and minimizing erosion. Active and some resistant organic components of the soil, along with microorganisms like fungi, participate in binding soil particles into larger aggregates.

However, maintaining a balance between organic matter addition and decomposition is crucial for sustaining a healthy level of organic matter in the soil. When addition is lower than decomposition, organic matter in the soil declines. Conversely, when addition exceeds decomposition, organic matter increases in the soil.

The abundance of organic matter in the soil is significant for crop planning and selecting suitable plant species. Anthropogenic factors such as land use practices, agricultural intensification, crop rotation, cover cropping, and organic fertilization greatly influence the organic matter content in the soil.


Soil is a crucial component of the environment, directly influencing the quality and effectiveness of agricultural crops. Soil properties such as structure, pH, porosity, and organic matter content determine its ability to support plant growth. In the United States, there are various types of soils, including acidic and alkaline soils, each with distinct properties requiring different approaches in cultivation.

Soil organisms, such as bacteria, fungi, and diverse microorganisms, play a key role in maintaining soil health and fertility. Knowledge about soil is essential for farmers and gardeners to maximize productivity and prevent soil degradation.

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