Post by Ask Jan on Sept 30, 2011 19:03:40 GMT -8
In soil science, humus refers to any organic matter that has reached a point of stability, where it will break down no further and might, if conditions do not change, remain as it is for centuries, if not millennia.
In agriculture, humus is sometimes also used to describe mature compost, or natural compost extracted from a forest or other spontaneous source for use to amend soil. It is also used to describe a topsoil horizon that contains organic matter (humus type).
Transformation of organic matter into humus
The process of “humification" can occur naturally in soil, or in the production of compost. The importance of chemically stable humus is thought by some to be the fertility it provides to soils in both a physical and chemical senses, though some agricultural experts put a greater focus on other features of it, such as disease suppressiveness. It helps the soil retain moisture by increasing microporosity, and encourages the formation of good soil structure. The incorporation of oxygen into large organic molecular assemblages generates many active, negatively charged sites that bind to positively charged ions (cations) of plant nutrients, making them more available by ion exchange. It allows soil organisms (microbes and animals) to feed and reproduce. Humus is often described as the “life-force” of the soil. Yet, it is difficult to define humus in precise terms; it is a highly complex substance, the full nature of which is still not fully understood. Humus can be differentiated from decomposing organic matter in that the latter is rough-looking material, with coarse plant remains still visible, whereas fully humified organic matter is uniform in appearance (a dark, spongy, jelly-like substance) and amorphous in structure, and may remain such for millennia or more. That is, it has no determinate shape, structure or character. However, humified organic matter, when examined under the microscope without any chemical treatment, may reveal tiny but clearly identifiable plant, animal or microbial remains that has been mechanically, but not chemically, degraded. In most recent literature, humus is clearly considered as an integral part of soil organic matter (SOM).
Plant remains (including those that passed through an animal gut and were excreted as feces) contain organic compounds: sugars, starches, proteins, carbohydrates, lignins, waxes, resins, and organic acids. The process of organic matter decay in the soil begins with the decomposition of sugars and starches from carbohydrates, which break down easily as detritivores initially invade the dead plant organs, while the remaining cellulose and lignin break down more slowly. Simple proteins, organic acids, starches and sugars break down rapidly, while crude proteins, fats, waxes and resins remain relatively unchanged for longer periods. Lignin, which is quickly transformed by white-rot fungi, is one of the main precursors of humus, together with by-products of microbial and animal activity. The humus, that is the product of this manifold process, is thus a mixture of compounds and complex life chemicals of plant, animal, or microbial origin, which has many functions and benefits in the soil. Earthworm humus (vermicompost) is considered by some to be the best organic manure there is.
Stability of humus
Compost that is readily capable of further decomposition is sometimes referred to as effective or active humus, though scientists would say that, if it is not stable, it is not humus at all. This kind of compost, rich in plant remains and fulvic acids, is an excellent source of plant nutrients, but of little value regarding long-term soil structure and tilth. Stable (or passive) humus consisting of humic acids and humins, on the other hand, are so highly insoluble (or so tightly bound to clay particles and hydroxides) that they cannot be penetrated by microbes and, therefore, are greatly resistant to further decomposition. Thus, stable humus adds few readily available nutrients to the soil, but plays an essential part in providing its physical structure. Some very stable humus complexes have survived for thousands of years. The most stable humus is that formed from the slow oxidation of black carbon, after the incorporation of finely powdered charcoal into the topsoil. This process is at the origin of the formation of the fertile Amazonian Dark Earths or Terra preta do Indio.
Benefits of soil organic matter and humus
The mineralization process that converts raw organic matter to the relatively stable substance that is humus feeds the soil population of microorganisms and other creatures, thus maintaining high and healthy levels of soil life.
The rate at which raw organic matter is converted into humus promotes (when fast) or limits (when slow) the coexistence of plants, animals, and microbes in terrestrial ecosystems.
Effective and stable humus (see below) are further sources of nutrients to microbes, the former providing a readily available supply, and the latter acting as a longer-term storage reservoir.
Decomposition of dead plant material causes complex organic compounds to be slowly oxidized (lignin-like humus) or to break down into simpler forms (sugars and amino sugars, aliphatic, and phenolic organic acids), which are further transformed into microbial biomass (microbial humus) or are reorganized (and still oxidized) in humic assemblages (fulvic and humic acids, humins), which bind to clay minerals and metal hydroxides. There has been a long debate about the ability of plants to uptake humic substances from their root systems and to metabolize them. There is now a consensus about humus as playing a hormonal role rather than a nutritional role in plant physiology.
Humus is a colloidal substance, and increases the soil's cation exchange capacity, hence its ability to store nutrients by chelation, as can clay particles; thus, while these nutrient cations are accessible to plants, they are held in the soil safe from leaching away by rain or irrigation.
Humus can hold the equivalent of eighty to ninety percent of its weight in moisture, and therefore increases the soil's capacity to withstand drought conditions.
The biochemical structure of humus enables it to moderate – or buffer – excessive acid or alkaline soil conditions.
During the humification process, microbes (bacteria and fungi) secrete sticky gum-like mucilages; these contribute to the crumb structure of the soil by holding particles together, allowing greater aeration of the soil. Toxic substances such as heavy metals, as well as excess nutrients, can be chelated (that is, bound to the complex organic molecules of humus) and prevented from entering the wider ecosystem, thereby detoxifying it.
The dark color of humus (usually black or dark brown) helps to warm up cold soils in the spring.
Humus is the stable, long lasting remnant of decaying organic material. It improves soil structure and increases water retention. Its nutritive qualities include trace elements and several important organic acids but do not include nitrogen or phosphorus.
In the strictest sense, humus is made up of humic substances composed of Carbon, Oxygen, and Hydrogen. These include humic acids, fulvic acids, and humins. Some Nitrogen may be present but not in any significant quantity. Plants obtain those first three elements by means other than soil so "pure" humus has no significant nutritive value. Mature compost is not pure humus, it also contains carbohydrates, lipids, and amino acids, not to mention living organisms feeding on the remaining undecomposed or partially decomposed material (cannot expect them to eat it all at once!). Many of these contain Nitrogen that is released gradually over time. Not all-organic matter in compost will be at the same stage of decomposition at any given time.
Humus or even soil organic matter in general is not perfect soil. There is no such thing as the perfect soil because needs of plants vary. Generally, a good soil contains a combination of sand, silt, clay and organic matter. For the purposes of gardening, agriculture, and even some soil science humus is considered synonymous with soil organic matter. This is the non-mineral portion of soil. Therefore, when a gardener talks about adding humus to soil they mean leaf mold or compost. When scientists talk about humus they have big numbers and formulas in their heads.
To a soil scientist, "humus" is the organic, non-cellular, long-lasting component of soil. It is organic because it is composed of chemicals containing carbon. It is mostly extremely stable carbon compounds with no phosphorus or nitrogen. Their stable form makes them difficult to break down by microorganisms. If humic compounds had N or P, microorganisms would try harder to attack them, but since they do not, they are not worth the effort. Humus is non-cellular because everything else in the cell breaks down and gets recycled into other organisms, leaving the humus in the soil but no longer within a cell. The term "humus" is tossed around loosely by gardeners to mean the organic material that makes soil brownish, (not all of which is humus). In nature, humus accumulates in soil because it lasts for hundreds or thousands of years. Humus often lasts in soil until a hot fire burns through the soil.
"Compost" is a matter of location and planning. Anything living starts decomposing when it dies. You call it compost when you put it in a pile and WATCH it decompose.
A dark brown or black colloidal mass of partially decomposed organic matter in the soil. It improves the fertility and water retention of the soil and is therefore important for plant growth
Humus is a complex organic substance resulting from the breakdown of plant material in a process called humification.
Humus is extremely important to the fertility of soils in both a physical and chemical sense.
You Can Produce Humus and Compost.
An easy old-time method of increasing soil organic content was to grow ryegrass or soybeans, and then plow them under as a green manure. You can do this in between harvests if you grow a winter cover crop. The same effect can be gotten by mixing purchased organic materials--such as peat--into the soil. However, avoid introducing weed seeds. This will be a hazard if you obtain manure from a local barn lot. There may be weed seeds in the hay, or even in piles of sawdust left to rot at the mills.
Such organics yield humus when they decompose, but they should be mostly decomposed when you use them. If organic materials high in carbohydrate s (such as sawdust or straw) are mixed fresh into soil, a temporary imbalance of fertility results until decay has progressed. The little organisms that cause rotting compete with garden plants for nitrogen. If you are mixing incompletely decomposed organics into your soil, you should add at least a pound of actual nitrogen to each 1,000 square feet or your plants may starve at the very time you think you are helping to nourish them.
Often organics are first put on as mulch (surface layer) only. Some decomposition occurs during the growing season, and then the residues are mixed into the soil.
Many gardeners prefer to have a compost pile where they dump weeds, fallen autumn leaves, and grass clippings, and allow them to decompose into humus. Practically anything that was once alive can be added, including garbage from the kitchen such as non-meat table scraps, egg cartons, paper towels, eggshells, coffee grounds, shredded paper from the office, etc. Various techniques are used, but the main objective is to encourage the microorganisms to attack the organics. These little organisms need moisture and air in order to flourish. Therefore, a compost heap should be arranged to drain adequately, but it should be dished out at the top to trap water rather than shed it. In some instances, purchased bacteria or earthworms are added, but usually nature supplies these adequately.
For quick composting, layers of rich soil are often interspersed between the organic material, possibly with lime and fertilizer added as well. Loosening or turning the compost aerates it and speeds the decomposition. A well-laid pile will function even in winter, for the internal activity releases heat.
The time it takes to produce humus, in favorable conditions, may be only a few weeks. However, if you are not in a hurry, you can pile things up as they accumulate, and they will gradually rot to black humus in the oldest part of the pile.
Using Humus to Improve Soil Organically
To convert leaves, grass clippings and kitchen scraps into humus, you will need to begin composting
Humus is the life of your soil. Without it, soil is inactive and unable to produce plants, grass or flowers. Humus is the loose, crumbly material that results from the decay of organic matter — leaves, grass clippings, garden waste, peat moss, kitchen scraps, or any such material.
Humus is important because it retains moisture in the soil, loosens the soil permitting better aeration and drainage, and encourages the increase of soil organisms that help make nutrients available to plants. It adds body to light soil and loosens heavy, sticky soils.
In the past, humus was assured in soil by the addition of barnyard manures. Since you probably do not live on a farm or have a horse, cow or goat, it is important to make your own humus through the process of composting.
Garden wastes in the form of compost are a source of humus that most gardeners fail to use, even though it is easy and effective to do so. Nearly every garden has room for a compost bin hidden by shrubbery or even a compost pile hidden somewhere in the yard. Here, leaves, grass clippings, weeds, spent flowers and vegetable plants and even vegetable waste from the kitchen are thrown into a compost heap.
If you are using a pile, it can reach a height of four or five feet, but keep the top flat or indented so that it catches rainwater and stays moist enough to continue breaking down process. If the season is dry, you can wet the pile now and then with the hose.
You can speed up the process of composting by turning your compost pile, or tumbling your compost bin. When the compost is loose and crumbly and the materials that went into it have lost their identity, then the compost is ready to go in your soil.
The time to make compost varies with the materials used, the weather, and the amount of stirring and other factors. Once you have finished compost, spread it one or two inches thick over your soil and work it in thoroughly. You will be amazed at how much better your plants will grow.
Mature compost is still organic matter and can be used when your planting instructions request it. Organic matter that hasn't decayed as far as compost shouldn't normally be used directly on plants because the nutrient balance and pH can get all out of whack as it decays (too much nitrogen in fresh manure, or nitrogen depletion as woodchips decompose) and because it may still contain toxic substances (fungal diseases, weed seeds, or toxic bacteria).
Humus has no nutritive value. It is also impossible to get hold of since it cannot be manufactured. It also cannot be produced from decaying organic matter in a reasonably pure form on any sensible timescale. Lastly, because nobody knows what humus is exactly (chemically), you may find stuff sold as "humus" or "humates" or something similar, it is buyer beware, you really have no guarantees about what is in the bag.
Humus is good because it has extremely high absorption abilities. It can hold and release water and nutrients as needed. It also improves the physical structure of soil so that it is crumbly and aerated instead of a nasty clay mess or an arid beach.
Humus, nonliving, finely divided organic matter in soil, derived from microbial decomposition of plant and animal substances. Humus, which ranges in color from brown to black, consists of about sixty percent carbon, six percent nitrogen, and smaller amounts of phosphorus and sulfur. As humus decomposes, its components are changed into forms usable by plants.
Humus is classified into mor, mull, or moder formations according to the degree of its incorporation into the mineral soil, the types of organisms involved in its decomposition, and the vegetation from which it is derived.
A MOR formation, or raw humus condition, occurs in soil that has few micro- organisms or animals, such as earthworms, to decompose the organic matter that lies on the soil surface. Below this surface-litter layer is a distinct, strongly compacted humus layer; a layer of mineral soil underlies the humus. Fungi and small arthropods are the most common organisms. MOR soils are usually acidic (low pH) and are characteristic of coniferous forest areas, especially in cold regions and at high altitudes.
A MULL humus formation is characteristic of hardwood forests, deciduous forests, or grasslands in warm, humid climates. The porous, crumbly humus rapidly decomposes and becomes well mixed into the mineral soil, so that distinct layers are not apparent. Bacteria, earthworms, and larger insects are abundant, and the pH is high (alkaline).
A MODER humus formation is intermediate between mor and mull extremes. Moder is sometimes known as insect mull because its distinguishing characteristic is the presence of many arthropod fecal pellets. Chains of these pellets bind plant debris and mineral particles together into a netlike structure. A moder formation contains more organic material than a mull formation, but this material is not as well mixed with mineral components.
Farmers value humus and gardeners because it provides nutrients essential for plant growth, increases soil water absorption, and improves soil workability.
A major component of soils is organic matter produced by organisms. The total organic matter in soil, except for materials identifiable as undecomposed or partially decomposed biomass is called humus. This solid, dark-colored component of soil plays a significant role in the control of soil acidity, in the cycling of nutrients, and in the detoxification of hazardous compounds.
• Accumulation of humic acid one of two classes of natural acidic organic polymer that can be extracted from humus found in soil, sediment, or aquatic environments. The process by which humic acid forms in humus is not well understood, but the consensus is that it accumulates gradually as a residue from the metabolism of microorganisms. Its structure is unlike that of proteins or carbohydrates.
• formation by soil organisms Though soil organisms have become less important in agriculture due to the development of synthetic fertilizers, they play a vital role in woodlands, especially in the creation of humus, a finely separated complex of organic materials composed of decaying leaves and other vegetable matter.
• Formation of fossil. Much of the undecomposed organic matter in sediment and sedimentary rocks is humus, plant matter that accumulates in soil. Other important organic constituents include peat, humic organic matter that collects in bogs and swamps
Humus controls and regulates many soil functions, as well as plant growth. The better the humus count in the soil, the healthier and more productive soil will be. Regardless of the program, one uses in farming operations, the higher the humus count, the better the crop yield. Good humus count in soil will hold soil moisture longer, thus less water is required for crop production. Good humus count reduces both water and wind erosion of soil.
There seems to be a false belief among farmers today that crop residue and organic matter are the same as humus. Organic matter is crop residue that is in the process of decomposition, while humus is decomposed organic matter. Experts agree 25,000 pounds of corn stalk residue per acre, broken down with nitrogen fertilizer, yields less than one percent humus count per acre. They also state it is impossible to attain a two percent humus count, even if 50,000 pounds of corn residue is plowed down every year for five years in sequence, when using today is high salt index fertilization programs. With modern chemical farming practices, very few farmers attain a two percent humus count.
Carbon compounds make up fifty percent of humus itself. The carbon compounds contained in the humus are used by microorganisms through the process of fermentation and respiration, converting it into high-energy values used by the plant for growth. Other portions of the carbon may be spent, or used in the oxidation of mineral compounds into simpler and more available forms of energies. Humus as a concentrate of carbon and energy compounds, aids bacteria to survive excessive moisture, cold or dry conditions. Humus enables bacteria to carry out antibiotic effects in the soil, as well as aiding bacteria interrelations with plant roots.
Humus absorbs the highly active non-nutrient hydrogen sources present in the soil and makes them immediately available as a food source for assimilation and usage by the plant. The humus colloid, or particle, will absorb and hold three times more mineral cations, water, and carbon compounds in the soil that are in a readily usable form for the plant to utilize. This means better crop growth and production. The humus colloids also protect (buffer) the microbial and plant systems against excessive sodium, magnesium, potassium, as well as other positive charged minerals, as the humus colloid carries a negative charged ion. The humus colloid also acts to buffer and enhance the four basic anions: carbon, nitrogen, phosphorous and sulfur, in their system of nutritional service to the soil and plants. When carbon, nitrogen, phosphorus and sulfur are associated with humus, they become nutrients for both soil microbe activity as well as plant growth.
The humic acids, carbonic acids and carbon energy are activated, either through the association of properly digested organic residues, or from a balanced decaying of crop residues. It is well known that humic acid controls many of the vital processes in soils and in plants (i.e. - absorption, photosynthesis, evaporation, growth, etc.). If the soil is too acidic, or too alkaline, or high in salt content, crops will not attain their full production potential. Therefore, if the soil contains enough humus, the plant is healthier and will be less susceptible to insect damage.
The natural process of humus production starts with crop residues. This residue can be broken down into organic matter with proper moisture and microorganism activity. The nutrients in the organic matter are still not available to the plant. The final stage of decomposition is when the organic matter is broken down into humus. The nutrients in the humus are readily available to the plant. Micro and macro-organisms such as earthworms along with proper climatic conditions are essential to complete the process of decomposition to produce humus. With the coming of the chemical age in farming in the late 1940’s, this natural cycle of humus production has in many cases been destroyed.
The chemicals have destroyed many of the beneficial organisms needed to produce humus, while at the same time have mined the humus from soils. Today, many of our once fertile agricultural soils have become nothing more than a growing medium. In many cases, farmers are using more and more chemicals while producing fewer yields at a higher cost of production.
To restore once fertile soils, two things must be accomplished: Restore humus back into soils and restore the natural biological balance to soils.
How to restore humus and biological balance back into soils
There are many forms of humic acids available on the market today. Most of the humic acids on the market are passive humic acids. They are mined from mineral deposits of lignite, a low-grade coal deposit, found in many areas throughout the world. Passive humic acids overall contain a small percentage of humic acid, most of which is not in a form that the plant can use.
Soil without humus is lifeless –it is dead soil. Humus, the indigestible part of decomposed organic matter, literally converts soil into a living thing because it provides a habitat for beneficial fungi that feed nutrients to many plant families and microorganisms that keep soil-borne plant diseases under control. It also keeps soil more moisture retentive, yet better drained; improves soil structure; holds nutrients in a form that are easily absorbed by plants; insulates plant roots by keeping topsoil cooler in summer and warmer in winter, and acts as a buffer against extremes in soil pH through a complex exchange of electrically-charged particles in the soil. Regular replacement of humus in soil is essential to healthy plant growth. Humus can be added to soil as compost, green manures, well rotted herbifierous animal manures, poultry manures, organic mulches, decaying (roots and plants). Plants from arid soil areas have evolved to require only small amounts of humus. Humus is essentially the organic material present in soil that has ceased breaking down. It is a large source of minerals and nutrients in soil and plays a large role in controlling pH and cation exchange capacity in soils. Generally, soils with high amounts of humus will have a low pH and high CEC.
Organic matter - stuff that came from biological sources. Diamonds and graphite do not decompose. This includes humus, mature compost, immature compost, freshly cut plants, live plants, garden waste, grass clippings, hay, leaf mold, hair, kitchen scraps (vegetable), egg shells, coffee grounds, etc.
Humus - (soil science) that portion of the soil that has fully broken down and is thus stable.
Compost - organic matter in a purposeful state of partial decomposition. The purposeful part is important. Dead stuff on the ground is NOT compost, just decaying organic matter. It is the controlled or semi-controlled conditions that make it compost.
Immature Compost - compost that has not undergone enough decomposition to be of maximal benefit. This definition is thus use-specific, but usually implies insufficient pathogen destruction, lack of friability, poor moisture retention, and active generation of metabolic gasses. Primarily still in bacterial stage of decomposition.
Mature Compost - compost that has decomposed to the point of maximum usefulness. Usually in the fungal/actinomycete stage.
All mature compost is organic matter, but not all-organic matter is mature compost. If what you are after is soil conditioning alone, then the terms humus and mature compost are interchangeable.
Humus also has a high cation exchange capacity, which means it acts as a veritable storehouse for plant nutrients, something that can be especially important for those with sandy soils.
“Understanding Humus” www.youtube.com/watch?v=3Vcoo3DxYQk
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