How Does Organic Material Enter Soil?

The nutrient cycle ensures that organic material is continuously recycled to provide nourishment for soil organisms and plants. Understanding how organic matter enters the soil is key to improving soil quality and plant growth.

If you’re short on time, here’s a quick answer: Organic material enters the soil through the decomposition of plant and animal residues, root exudates from living plants, and the addition of manure and compost.

Decomposition of Plant and Animal Residues

Organic material enters soil through the process of decomposition. When plant and animal residues break down, they release nutrients and organic matter into the soil, enriching it and providing essential resources for plant growth.

Leaf Litter and Crop Residue

One of the main sources of organic material in soil is leaf litter and crop residue. When leaves fall from trees or crops are harvested, they decompose and release nutrients into the soil. This process is crucial for nutrient cycling in ecosystems.

Leaf litter and crop residue provide a diverse range of organic matter, including cellulose, lignin, and other compounds. These materials break down through the action of microorganisms such as bacteria and fungi. As they decompose, they release carbon, nitrogen, phosphorus, and other essential elements into the soil.

According to a study conducted by the University of California, Davis, leaf litter decomposition can vary depending on factors such as temperature, moisture, and the type of plant material. For example, leaves from deciduous trees tend to decompose faster than those from evergreen trees.

Dead Roots, Fallen Trees, and Branches

Dead roots, fallen trees, and branches also contribute to the organic matter in soil. When trees die or branches break off, they eventually decompose and become part of the soil ecosystem.

These organic materials provide a rich source of nutrients and carbon. Decomposition of woody materials can be slower than leaf litter decomposition, as the structure of wood takes longer to break down. However, over time, the nutrients stored in dead roots, fallen trees, and branches are released into the soil, supporting the growth of new plants.

In a study published in the journal Soil Biology and Biochemistry, researchers found that dead roots can contribute significantly to soil organic carbon stocks. They found that fine roots, in particular, play a crucial role in carbon sequestration in soil.

Animal Wastes and Carcasses

Animal wastes and carcasses also play a role in adding organic material to soil. When animals defecate or urinate, their waste contains nutrients that can be absorbed by plants and contribute to soil fertility.

Similarly, when animals die and decompose, their carcasses release nutrients and organic matter into the soil. This process helps to sustain the soil ecosystem and provides resources for other organisms.

A study published in the journal Soil Science Society of America Journal found that animal manure can significantly increase soil organic matter content, improving soil fertility and crop productivity.

Root Exudates from Living Plants

When it comes to organic material entering the soil, one significant source is the release of root exudates from living plants. Root exudates are substances that are actively secreted by plant roots into the surrounding soil. These exudates play a crucial role in the soil’s nutrient cycling and microbial activity, ultimately influencing the overall health and fertility of the soil.

Sugars and Amino Acids Released by Roots

One of the main components of root exudates are sugars, such as glucose and fructose, which are released by the plant roots. These sugars serve as an energy source for soil microorganisms, stimulating their growth and activity. As microorganisms consume these sugars, they release byproducts that contain essential nutrients, making them available for the plants to absorb.

In addition to sugars, plants also release amino acids through their roots. Amino acids are the building blocks of proteins and are vital for the growth and development of plants. By releasing amino acids into the soil, plants not only provide a nutrient source for soil microorganisms but also attract beneficial microbes that can form symbiotic relationships with the plants.

Role of Mycorrhizae

Mycorrhizae are symbiotic associations between plant roots and specialized fungi. These fungi form a network of thread-like structures called hyphae, which extend into the soil and greatly increase the surface area available for nutrient uptake. In return, the fungi receive sugars and other organic compounds from the plant, fueling their growth.

The mycorrhizal fungi play a crucial role in the transfer of organic material into the soil. They can break down complex organic compounds, such as lignin and cellulose, into simpler forms that can be readily absorbed by plants. This breakdown process releases nutrients into the soil, making them more accessible to both the fungi and the plants.

Research has shown that mycorrhizal associations can significantly enhance nutrient uptake by plants, improve soil structure, and increase the overall productivity of ecosystems. Therefore, these symbiotic relationships are essential for the efficient cycling of organic material in the soil.

For more information on the role of root exudates and mycorrhizae in soil health, you can visit or

Manure and Compost Additions

Farm Animal Manure

One of the main ways organic material enters soil is through the addition of farm animal manure. Farmers have been using manure as a natural fertilizer for centuries. Manure contains a variety of organic matter, including animal waste, bedding materials, and leftover feed. When manure is applied to soil, it breaks down over time, releasing nutrients and organic matter that improve soil fertility and structure.

Farm animal manure is rich in essential nutrients such as nitrogen, phosphorus, and potassium, which are important for plant growth. It also contains beneficial microorganisms that help break down organic matter and promote nutrient availability for plants. Manure can be sourced from various farm animals, including cows, pigs, chickens, and horses. Each type of manure has different nutrient compositions, so farmers choose the type that best suits their crops’ needs.

It’s important to note that the application of manure should be done carefully to avoid overloading the soil with nutrients, which can lead to environmental issues such as water pollution. Farmers follow specific guidelines and regulations to ensure proper manure management and minimize the impact on the environment.

Composted Organic Wastes

Another way organic material enters soil is through the addition of composted organic wastes. Composting is a natural process where organic materials, such as food scraps, yard trimmings, and plant residues, are decomposed by microorganisms into a nutrient-rich soil amendment.

Compost can be made on a small scale by homeowners or on a larger scale by municipal composting facilities. The composting process involves creating the right conditions for microorganisms to break down the organic materials. These conditions include a proper balance of carbon-rich (e.g., leaves, straw) and nitrogen-rich (e.g., food scraps, grass clippings) materials, adequate moisture, and good aeration.

Once the organic materials have decomposed, the resulting compost is added to soil to improve its structure, fertility, and water-holding capacity. Compost helps to increase the amount of organic matter in the soil, which in turn promotes the growth of beneficial soil organisms and improves overall soil health.

Composted organic wastes are a sustainable alternative to chemical fertilizers, as they recycle organic materials that would otherwise end up in landfills. By diverting organic waste from landfills and turning it into compost, we can reduce greenhouse gas emissions and create a valuable resource for our soils.

Other Contributors

In addition to the direct inputs of organic material from plant residues and animal waste, there are other contributors to the organic content of soil. These additional sources play a crucial role in maintaining soil fertility and supporting the growth of plants. Two significant contributors to organic material entering the soil are atmospheric deposition and sedimentation.

Atmospheric Deposition

Atmospheric deposition refers to the deposition of organic material from the atmosphere onto the soil surface. This can occur through various processes such as precipitation, dust deposition, and the settling of airborne particles. The organic material in the atmosphere can come from a variety of sources, including plant debris, pollen, and even microbial activity. When it rains or snows, these particles are carried to the ground, where they settle and contribute to the organic content of the soil.

Atmospheric deposition can have both positive and negative impacts on soil health. On the positive side, it can provide a source of nutrients, such as nitrogen, that are essential for plant growth. However, excessive deposition of pollutants, such as heavy metals or acid rain, can have detrimental effects on soil health and the organisms residing in it. Monitoring and managing atmospheric deposition is crucial to maintaining a healthy soil ecosystem.


Sedimentation refers to the deposition of organic material from water bodies onto the soil surface. When rivers, lakes, or oceans overflow or experience high water flow rates, they can carry organic matter with them. This organic material can range from plant debris and algae to sediment-bound nutrients. As the water slows down and loses its energy, it deposits the organic matter onto the soil.

Sedimentation plays a vital role in nutrient cycling and soil fertility. The deposited organic material can provide essential nutrients for plant growth and act as a source of organic carbon for soil microorganisms. Additionally, sedimentation can contribute to soil formation processes, such as the accumulation of organic-rich layers in wetland ecosystems.

To mitigate the negative impacts of sedimentation, it is crucial to implement proper land management practices that minimize soil erosion. This includes measures such as contour plowing, terracing, and the establishment of buffer zones along water bodies. By reducing soil erosion, we can preserve the organic material in the soil and maintain its fertility for future generations.


The soil food web depends on the regular replenishment of organic matter. By understanding the diverse sources of organic material, from decaying plant residues to animal wastes, we gain insight into how to manage soils sustainably.

Encouraging the cycling of organic matter through composting and cover cropping are examples of ways we can work with, rather than against, the natural processes that build fertile, resilient soils.

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