Soils that formed under prairie vegetation usually have native organic matter levels at least twice as high as those formed under forest vegetation.
Building soil organic matter is a long-term process but can be beneficial. Here are a few ways to do it. A good supply of soil organic matter is beneficial in crop or forage production. Consider the benefits of this valuable resource and how you can manage your operation to build, or at least maintain, the organic matter in your soil.
Barber, S. New York: Wiley, Brady, N. The Nature and Properties of Soils. New York: Macmillan Publishing Co. Plaster, E. Soil Science and Management. Albany: Delmar Publishers, Tisdale, S. Soil Fertility and Fertilizers. New York: Macmillan, Eddie Funderburg, Ed. What is Organic Matter? Beneficial soil organisms become more numerous and active with diverse crop rotations and higher organic matter levels.
Air quality, water quality, and agricultural productivity improve Dust, allergens, and pathogens in the air immediately decline. Sediment and nutrient loads decline in surface water as soon as soil aggregation increases and runoff decreases. Ground and surface water quality improve because better structure, infiltration, and biological activity make soil a more effective filter. Crops are better able to withstand drought when infiltration and water holding capacity increase.
Organic matter may bind pesticides, making them less active. As microorganisms increase their activity during warmer weather that occurs predominantly in the spring and summer, greater amounts of nutrients are cycled from organic forms into those that are inorganic and plant available. In addition, O. Soil Structure Organic matter causes soil particles to bind and form stable soil aggregates, which improves soil structure.
Water Holding Capacity Soils with higher O. Organic matter behaves similar to 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 O. Figure 2 shows the increase in plant available water with higher O. Increasing O. Source: Adapted from data by Hudson, Erosion Control Greater aggregate stability is often the result of soils with more O.
This part of soil organic matter includes a wide variety of microorganisms, such as bacteria, viruses, fungi, protozoa and algae. It even includes plant roots and the insects, earthworms and larger animals, such as moles, woodchucks and rabbits that spend some of their time in the soil. Microorganisms, earthworms and insects feed on plant residues and manures for energy and nutrition, and in the process they mix organic matter into the mineral soil.
In addition, they recycle plant nutrients. Sticky substances on the skin of earthworms and other materials produced by fungi help bind particles together.
This helps to stabilize the soil aggregates, which are clumps of particles that make up good soil structure. Sticky substances on plant roots as well as the proliferation of fine roots and their associated mycorrhizae help promote development of stable soil aggregates.
Plant roots also interact in significant ways with the various microorganisms and animals living in the soil. Another important aspect of soil organisms is that they are in a constant struggle with each other Figure 2. Further discussion of the interactions between soil organisms and roots, and among the various soil organisms, is provided in Chapter 4.
A multitude of microorganisms, earthworms and insects get their energy and nutrients by breaking down organic residues in soils. At the same time, much of the energy stored in residues is used by organisms to make new chemicals as well as new cells. How does energy get stored inside organic residues in the first place? Green plants use the energy of sunlight to link carbon atoms together into larger molecules. This process, known as photosynthesis , is used by plants to store energy for respiration and growth, and much of this energy ends up as residues in the soil after the plant dies.
The dead. In some cases, just looking at them is enough to identify the origin of the fresh residues Figure 2. This part of soil organic matter is the active, or easily decomposed, fraction.
This active fraction of soil organic matter is the main supply of food for various organisms—microorganisms, insects and earthworms—living in the soil. Organic chemical compounds produced during the decomposition of fresh residues also help to bind soil particles together and give the soil good structure.
Some organic molecules directly released from cells of fresh residues, such as proteins, amino acids, sugars and starches, are also considered part of this fresh organic matter. These molecules generally do not last long in the soil. Their structure makes them easy to decompose because so many microorganisms use them as food. Some cellular molecules such as lignin are decomposed, but it takes longer for organisms to do so.
This can make up a large fraction of the soil organic matter in poorly drained soils, like peats and mucks, as well as wetlands that have been taken into agricultural production. The very dead. This includes other organic substances in soils that are difficult for organisms to decompose. Some use the term humus to describe all soil organic matter. Humus is protected from decomposition mainly because its chemical structure makes it hard for soil organisms to utilize.
Identifiable fragments of undecomposed or partially decomposed residue, including remains of microorganisms, can be held inside aggregates in spaces too small for organisms to access. Because much of soil organic matter is so well protected from decomposition, physically and chemically, its age in soils can be as high as hundreds of years. But even though humus is protected from decomposition, its chemical and physical properties make it an important part of the soil.
Humus holds on to some essential nutrients and stores them for slow release to plants. Some medium-size molecules also can surround certain potentially harmful chemicals, like heavy metals and pesticides, and prevent them from causing damage to plants and the environment. The same types of molecules can also make certain essential nutrients more available to plants. Good amounts of soil humus and fragments of crop residues can lessen drainage and compaction problems that occur in clay soils.
They also improve water retention in sandy soils by enhancing aggregation, which reduces soil density, and by holding on to and releasing water. Another type of organic matter, one that has gained a lot of attention lately, is usually referred to as black carbon or char. Many soils contain some small pieces of charcoal, the result of past fires of natural or human origin.
Some, such as the black soils of Saskatchewan, Canada, may have relatively high amounts of char, presumably from naturally occurring prairie fires. However, an increased interest in charcoal in soils has come about mainly through the study of the soils called dark earths, the terra preta de indio that are on sites of long-occupied villages in the Amazon region of South America that were depopulated during the colonial era.
The soil charcoal was the result of centuries of cooking fires and in-field burning of crop residues and other organic materials. The manner in which the burning occurred—slow burns, perhaps because of the wet conditions common in the Amazon—produced a lot of char material and not as much ash as occurs with more complete burning at higher temperatures. These soils were intensively used in the past but have been abandoned for centuries.
Still, they remain much more fertile than the surrounding soils, partially due to the high inputs of nutrients in animal and plant residue that were initially derived from the nearby forest, and they yield better crops than surrounding soils typical of the tropical forest. Part of this higher fertility—the ability to supply plants with nutrients with very low amounts of leaching loss—has been attributed to the large amount of black carbon and the high amount of biological activity in the soils even centuries after abandonment.
Charcoal is a very stable form of carbon that helps maintain relatively high cation exchange capacity and supports biological activity by providing suitable habitat. However, char does not provide soil organisms with readily available food sources as do fresh residues and compost. People are experimenting with adding biochar to soils, but this is likely not economical at large scales.
The quantity needed to make a major difference to a soil is apparently huge— many tons per acre—and may limit the usefulness of this practice to small plots of land, gardens and container plants, or as a targeted additive coating seeds.
Also, benefits from adding biochar should be considered in comparison to what might be gained when using the same source materials like wood chips, crop residues or food waste added directly to the soil, after composting or even after complete combustion as ash. Black carbon, produced by wildfires as well as by human activity and found in many soils around the world, is a result of burning biomass at around — degrees Fahrenheit under low oxygen conditions.
This incomplete combustion results in about half or more of the carbon in the original material being retained as char. The char, also containing ash, tends to have high amounts of negative charge cation exchange capacity , has a liming effect on soil, retains some nutrients from the wood or other residue that was burned, stimulates microorganism populations, and is very stable in soils.
Although many times increases in yield have been reported following biochar application—probably partially a result of increased nutrient availability or increased pH—sometimes yields suffer. Legumes do particularly well with biochar additions, while grasses frequently become nitrogen deficient, indicating that nitrogen may be deficient for a period following application. Biochar is a variable material because a variety of organic materials and burn methods can be used to produce it, perhaps contributing to its inconsistent effects on soil and plants.
The economic and environmental effects of making and using biochar depend on the source of organic material being converted to biochar, whether heat and gases produced in the process are utilized or just allowed to dissipate, the amount of available oxygen during biochar production, and the distance from where it is produced to the field where it is applied.
On the other hand, when used as a seed coating, much less biochar is needed per acre, and it may still stimulate seedling growth and development. Note: The effects of biochar on raising soil pH and immediately increasing calcium, potassium, magnesium, etc. These effects can also be obtained by using more completely burned material, which contains more ash and little black carbon.
Carbon and organic matter. Soil carbon is sometimes used as a synonym for organic matter , although the latter also includes nutrients and other chemical elements. Because carbon is the main building block of all organic molecules, the amount in a soil is strongly related to the total amount of all the organic matter: the living organisms plus fresh residues plus well-decomposed residues.
When people talk about soil carbon instead of organic matter, they are usually referring to organic carbon, or the amount of carbon in organic molecules in the soil. The amount of organic matter in soils is about twice the organic carbon level.
However, in many soils in glaciated areas and semiarid regions it is common to have another form of carbon in soils—limestone, either as round concretions or dispersed evenly throughout the soil. Lime is calcium carbonate, which contains calcium, carbon and oxygen. This is an inorganic mineral form of carbon. Even in humid climates, when limestone is found very close to the surface, some may be present in the soil. In those cases the total amount of soil carbon includes both inorganic and organic carbon, and the organic matter content could not be estimated simply by doubling the total carbon percent.
Normal organic matter decomposition that takes place in soil is a process that is similar to the burning of wood in a stove. When burning wood reaches a certain temperature, the carbon in the wood combines with oxygen from the air and forms carbon dioxide.
As this occurs, the energy stored in the carbon-containing chemicals in the wood is released as heat in a process called oxidation. The biological world, including humans, animals and microorganisms, also makes use of the energy inside carbon-containing molecules. This process of converting sugars, starches and other compounds into a directly usable form of energy is also a type of oxidation.
We usually call it respiration. Oxygen is used, and carbon dioxide and heat are given off in the process. A fertile and healthy soil is the basis for healthy plants, animals and humans. And soil organic matter is the very foundation for healthy and productive soils. Understanding the role of organic matter in maintaining a healthy soil is essential for developing ecologically sound agricultural practices.
But how can organic matter, which only makes up a small percentage of most soils, be so important that we devote the three chapters in this section to discuss it? The reason is that organic matter positively influences, or modifies the effect of, essentially all soil properties, and it is what makes the soil fertile.
Organic matter is essentially the heart of the story, but, as we will discuss later, certainly not the only part. In addition to functioning in a large number of key roles that promote soil processes and crop growth, soil organic matter is a critical part of a number of global and regional cycles.
Although gravel and sand hydroponic systems, and even aeroponics where a nutrient solution is sprayed directly on plant roots without soil, can grow excellent crops, large-scale systems of this type may have ecological problems and make sense economically only for a limited number of high-value crops grown close to their markets. However, as soil organic matter decreases, it becomes increasingly difficult to grow plants, because problems with fertility, water availability, compaction, erosion, parasites, diseases and insects become more common.
Ever higher levels of inputs—fertilizers, irrigation water, pesticides and machinery—are required to maintain yields in the face of organic matter depletion. But if attention is paid to proper organic matter management, the soil can support a good crop with less need for expensive fixes. In a Maryland experiment, researchers saw an increase of approximately 80 bushels of corn per acre when organic matter increased from 0.
Part of the explanation for this influence is the small particle size of the well-decomposed portion of organic matter, the humus. Its large surface area—to—volume ratio means that humus is in contact with a considerable portion of the soil.
0コメント