Soil Fundamentals: Composition, Agriculture, and Organic Matter

Relief: Earth's Surface and Water Movement

Relief refers to the Earth's surface, which influences the movement of water.

Time: Soil Formation and Evolution

Time influences the formation, development, and evolution of soil.

Soil Profile: Layers with Distinct Characteristics

A soil profile is a set of horizons, which are layers with different characteristics.

Horizon A: Surface Layer and Eluviation

Horizon A is always on the surface and has the highest biological activity. Clay loss occurs in this layer, making it an eluvial horizon (meaning it has lost particles).

Horizon B: Clay Accumulation and Illuviation

Horizon B has a large clay content. It is an illuvial horizon (meaning it gains particles).

Horizon C: Parent Material Layer

Horizon C is similar to the original parent material and is little affected by soil-forming factors.

Soil Texture: Sand, Silt, and Clay Proportions

Soil texture refers to the percentage proportion of sand, silt, and clay. Different combinations of these particles result in different kinds of soils. For example, loam soil has a balance between the three. Other types, like clay loam or silty clay loam, depend on the dominant particle size.

Transgenic Crops: Genetically Modified Plants

Transgenic crops involve the cultivation of plants that carry one or more genes stably incorporated into their genome (genes that are naturally absent) and are transmitted from generation to generation. An example is soybean.

Agroecosystems: Managed Agricultural Environments

An agroecosystem is an intermediate system between natural ecosystems and urban ecosystems. Abiotic factors are often improved with human intervention. The main biotic components are the planted crops. Key issues to consider regarding human impact on organic matter dynamics include:

• Stubble Management: Stubble is the main source of organic matter returned to the ground.
• Tillage Systems: Tillage disturbance increases oxygenation of the soil layer, leading to oxidation of organic matter.
• Productive Activity and Rotational Systems: Practices like direct seeding create a less oxidizing environment.
• Management Activities: Fertilization affects the population and activity of microorganisms. Irrigation can also influence these processes.

Deteriorated Soil: Lost Productivity and Structure

Deteriorated soil is soil that has totally or partially lost its ability to produce due to alterations in its physical, chemical, and biological properties, and has lost its structure.

Maintaining Soil Humus Levels

Several elements are crucial for maintaining the percentage of humus in the soil:

1. Crop Rotation: The choice of crop rotation is the first element.
2. Fallow Period: The fallow period, or the time between harvesting one crop and planting the next, allows for the humification process.
3. Cropping Practices: The timing of agricultural operations, intensity of land use, and type of machinery used are also important factors.

Organic Waste: Decomposition Precursors

Organic waste, such as plant and animal tissues, is partially decomposed by the action of soil microorganisms.

Humus: Stable Decomposed Organic Matter

Humus is the result of the complete decomposition of organic waste, jointly with soil minerals. It is a stable, dark, and odorless compound. Organic waste is initially processed by:

• Physical Action: Water, wind, animals, and human activities.
• Chemical Action: Water, light, acidity, and temperature.
• Biochemical Action: Microorganisms such as fungi and bacteria.

Soil Organic Matter Transformation Processes

Two key processes transform organic matter in soil:

• Mineralization: The formation of mineral compounds from organic waste.
• Humification: The formation of complex chemical compounds, known as humus.

Both processes occur simultaneously. They involve soil microorganisms and are influenced by factors such as plant characteristics, climate, soil type, relief, pH, rainfall, and the carbon-nitrogen (C:N) ratio of stover (crop residue). A higher C:N ratio leads to slower decomposition and more stable chemical compounds formed.