Organic Carbon – Organic Matter – soil Biology
What is it?
Of all the components of soil, organic matter is probably the most important and most misunderstood. Organic matter serves as a reservoir of nutrients and water in the soil, aids in reducing compaction and surface crusting, and increases water infiltration into the soil. Often, we think of organic matter as the plant and animal residues we incorporate into the soil. We see a pile of leaves, manure, or plant parts and think, “Wow! I’m adding a lot of organic matter to the soil.” This stuff is an organic material, not organic matter.
What’s the difference between organic material and organic matter?
Organic material is anything that was alive and is now in or on the soil. For it to become organic matter, it must be decomposed into humus. Humus is organic material that has been converted by microorganisms to a resistant state of decomposition. Organic material is unstable in the soil, changing form and mass readily as it decomposes. As much as 90 percent of it disappears quickly because of decomposition.
Organic matter is stable in the soil. It has been decomposed until it is resistant to further decomposition. Usually, only about 5 percent of it mineralizes yearly. That rate increases if temperature, oxygen, and moisture conditions become favourable for decomposition, which often occurs with excessive excavation and disruption. It is the stable organic matter that is analysed in the soil test.
What Are the Benefits of Organic Matter?
Nutrient Supply – Organic matter is a reservoir of nutrients that can be released to the soil. Each percent of organic matter in the soil releases 44 to 66 kilograms of nitrogen, 10 to 15 Kilograms of P2O5 (Phosphorous) and 4 to 6 kilograms of sulphur per year. The nutrient release occurs predominantly in the spring and summer, so summer crops benefit more from organic-matter mineralization than winter crops.
Water-Holding Capacity – Organic matter behaves somewhat like a sponge, with the ability to absorb and hold up to 90 percent of its weight in water. A great advantage of the water-holding capacity of organic matter is that the matter will release most of the water that it absorbs to plants. In contrast, clay holds great quantities of water, but much of it is unavailable to plants.
Soil Structure Aggregation – Organic matter causes soil to clump and form soil aggregates, which improves soil structure. With better soil structure, permeability (infiltration of water through the soil) improves, in turn improving the soil’s ability to take up and hold water.
The organisms living in the soil
Both large and small, play a significant role in maintaining a healthy soil system and healthy plants.
One of the main reasons we are interested in these organisms is because of their role in breaking
down organic residues and incorporating them into the soil. Soil organisms influence every aspect of
decomposition and nutrient availability. As organic materials are decomposed, nutrients become
available to plants, hummus is produced, soil aggregates are formed, channels are created for water
infiltration and better aeration, and those residues originally on the surface are brought deeper into
When soil organisms and roots go about their normal functions of getting energy for growth from
organic molecules, they “respire” using oxygen and releasing carbon dioxide to the atmosphere. (Of
course, as we take our essential breaths of air, we do the same.) An entire field can be viewed as
breathing as if it is one large organism. The soil is like a living being in another way too, it may get
“sick” in the sense that it becomes incapable of supporting healthy plants.
We classify soil organisms in several different ways. Each can be discussed separately or all organisms that do the same types of things can be discussed as a group. We also can look at soil organisms according to their role in the decomposition of organic materials. For example, organisms that use fresh residues as their source of food are called primary (1°), or first level, consumers of organic materials (see figure 4.1). Many of these primary consumers break down large pieces of residues into smaller fragments. Secondary (2°) consumers are organisms that feed on the primary consumers themselves or their waste products. Tertiary (3°) consumers then feed on the secondary consumers. Another way to treat organisms is by general size, such as very small, small, medium, large, and very large.
There is constant interaction among the organisms living in the soil. Some organisms help others, as when bacteria that live inside the earthworm’s digestive system help decompose organic matter. Although there are many examples of such mutually beneficial, or symbiotic, relationships, an intense competition occurs among most of the diverse organisms in healthy soils.
Organisms may directly compete for the same food. Some organisms naturally feed on others— nematodes may feed on fungi, bacteria, or other nematodes, and some fungi trap and kill nematodes. There are also fungi and bacteria that parasitize nematodes and completely digest their content.
Some soil organisms can harm plants, either by causing disease or by being parasites. In other words, there are “good” as well as “bad” bacteria, fungi, nematodes, and insects. One of the goals of agricultural production systems should be to create conditions that enhance the growth of beneficial organisms, which are the clear majority while decreasing populations of those few that are potentially harmful. Compacted and anaerobic soils are an ideal environment for harmful organisms
Symptoms of poor soil quality
Poor plant growth or plant loss, weed infestations, water pooling after rainfall or reticulation applications. High disease and pest pressure from beetles and larvae, poor root growth and plant density are all signs of an unhealthy soil profile.
Increasing the quality of a soil
Enhancing it as a habitat for plant roots and beneficial organisms can take a lot of thought and action over many years. Applications of a quality compost to lift (SOM) will assist with the promotion of soil quality (if you build it they will come) adage. Soil biology will migrate and multiply if given the right conditions to do so. Applications of humates, fish and kelps will provide food sources for biology numbers to increase.
All actions taken to improve soil health should contribute to one or more of the following: (a) growing healthy plants, (b) reducing pests, and (c) increasing beneficial organisms. First, various practices to build up and maintain high levels of soil organic matter are key. Second, developing and maintaining the best possible soil physical condition often require other types of practices, in addition to those that directly impact soil organic matter. Paying better attention to soil tilth and compaction is more important than ever because of the ever-increasing variety of uses our open spaces are required to facilitate.
Additions of organic matter – to improve soil structure (increases the ability of the soil to hold onto fertiliser applications and assists with minimizing nutrient leaching through the soil profile) Applications of compost tea – to build soil biology and increase nutrient cycling. Applications of bio-stimulants, to increase and promote the beneficial biology for a more sustainable soil profile.
The overall strategies of Adam Davey Consulting are based around sound crop and soil management, focusing on prevention of factors that might limit plant growth. It is recommended to carry out soil/tissue and Biology testing to establish a management program, this can then be used as a benchmark for program efficacy. Regeneration of the soil assists managers in a multitude of situations, reducing the effects and promotion of harmful pathogens that thrive in poor `soil health` conditions. These strategies are to grow healthy plants with enhanced defense capabilities, deter pests and enhance beneficial organisms while having a greatly reduced impact on the environment. Good organic matter management goes a long way toward providing good plant nutrition in an environmentally sound way, with the addition of modern day products and methods, results can be improved greatly.
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