Difference between revisions of "Humus"

Latest revision as of 18:23, 15 November 2013

Topic in Gardening courses. By John Eagles.

Calcareous Soil Profile, Seven Sisters Country Park - The top layer is dark humus. Below this a bleached horizon with leached out nutrients. Below that a darker reddish layer of redisposition. At the base the weathered bedrock (chalk). The unweathered chalk is hidden.

Humus is the part of organic matter in the soil that is resulting from decomposition of plant and animal residues. Humus has reached a point of stability and won't break down easily by microorganisms.

In most soils the percentage of humus ranges from two to ten percent. In peat bog it is up to 90 percent. The average composition is 58 % Carbon, 5 % Nitrogen, several acids. The C:N ratios varies from 10:1 to 12:1.^[1]

Humus improves the physical condition of the soil. It contains essential plant nutrients and it improves the soil's capacity to hold water. It prevents leaching of water soluble plant nutrients and it improves the microbial activity of a soil. Soils with humus have better aeration and drainage by making the soil more porous.

Organic matter is decomposed by animals (for example earth worms) and microorganisms in the soil. Most of these soil microorganisms need oxygen and they always need water. They work faster in higher temperatures. This means that within regions of similar moisture conditions, the organic matter content of soil decreases from north to south.

Tropical regions have very little or no humus in their soil. Along the Mississippi River, where soil moisture conditions remain rather similar from south to north, we might find 2 percent in Arkansas, 3 percent in Missouri and over 4 percent in Wisconsin. Hot desert soils have virtually no organic matter.^[2]

Humus can also be made by humans. An example are the Terra preta soils that were made by tribes and cultures that flourished in the Amazon before the Spaniards came.

Definitions of humus

An environment where humus is formed

"Humus is the excrement of soil animals, primarily earthworms, but including that of some other species that, like earthworms, are capable of combining partially decomposed organic matter and the excrement of other soil animals with clay to create stable soil crumbs resistant to further decomposition or consumption."^[3]

"Humus is the stable, long lasting remnant of decaying organic material. It improves soil structure and increases water retention. It's nutritive qualities include trace elements and several important organic acids but do not include nitrogen or phosphorus."^[4]

"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, micro-organisms would try harder to attack them, but since they don't, they aren't 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" gets 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."^[4]

Prairies, or grassland in general, is an environment where much humus can be formed.

"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 (can't 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."^[4]

Humic acid

Humic acid^[5] is a principal component of humic substances. It is not a single acid but a complex mixture of many different acids. Humic acids can form complexes with ions that are commonly found in soils creating humic colloids.^[6]

References

↑ Soil Humus - My Agriculture Information Bank
↑ Maintaining Soil Humus Wilderness Survival
↑ Making Humus
↑ ^4.0 ^4.1 ^4.2 What is the real difference between compost and humus? GardenWeb
↑ Humic acid - Wikipedia
↑ A colloid is a substance microscopically dispersed evenly throughout another substance. For example, milk is an emulsified colloid of liquid butterfat globules dispersed within a water-based solution.

External links

Humic acid Wikipedia
Humus Wikipedia
Maintaining soil humus
Making Humus
Soil Humus My Agriculture Information Bank
What is the real difference between Compost and Humus? GardenWeb

Videos

Comments

[1] Soil Humus - My Agriculture Information Bank

[2] Maintaining Soil Humus Wilderness Survival

[3] Making Humus

[GardenWeb-4] 4.0 ^4.1 ^4.2 What is the real difference between compost and humus? GardenWeb

[5] Humic acid - Wikipedia

[6] A colloid is a substance microscopically dispersed evenly throughout another substance. For example, milk is an emulsified colloid of liquid butterfat globules dispersed within a water-based solution.

[1]

[2]

[3]

[4]

[5]

[6]

@@ Line 1: / Line 1: @@
 : ''Topic in [[Gardening courses]]. By [[User:John|John Eagles]].''
-: ''This page is under construction!''
+[[File:Calcareous Soil Profile, Seven Sisters Country Park - geograph.org.uk - 1280181.jpg|thumb|400px|right|Calcareous Soil Profile, Seven Sisters Country Park - The top layer is dark humus. Below this a bleached horizon with leached out nutrients. Below that a darker reddish layer of redisposition. At the base the weathered bedrock (chalk). The unweathered chalk is hidden.]]
-[[File:Calcareous Soil Profile, Seven Sisters Country Park - geograph.org.uk - 1280181.jpg|thumb|300px|right|Calcareous Soil Profile, Seven Sisters Country Park - The top layer is dark humus. Below this a bleached horizon with leached out nutrients. Below that a darker reddish layer of redisposition. At the base the weathered bedrock (chalk). The unweathered chalk is hidden.]
+Humus is the part of organic matter in the soil that is resulting from decomposition of plant and animal residues. Humus has reached a point of stability and won't break down easily by microorganisms.
-Humus is organic matter in the soil resulting from decomposition of plant and animal residues. Humus has reached a point of stability and won't break down easily by microorganisms.
 In most soils the percentage of humus ranges from two to ten percent. In peat bog it is up to 90 percent. The average composition is 58 % Carbon, 5 % Nitrogen, several acids. The C:N ratios varies from 10:1 to 12:1.<ref>[http://agriinfo.in/default.aspx?page=topic&superid=5&topicid=137 Soil Humus - My Agriculture Information Bank]</ref>
 Humus improves the physical condition of the soil. It contains essential plant nutrients and it improves the soil's capacity to hold water. It prevents leaching of water soluble plant nutrients and it improves the microbial activity of a soil. Soils with humus have better aeration and drainage by making the soil more porous.
----
-Humus is the stable, long lasting remnant of decaying organic material. It improves soil structure and increases water retention. It's nutritive qualities include trace elements and several important organic acids but do not include nitrogen or phosphorus"
-humus has no nutritive value. It's also impossible to get hold of since it can't be manufactured. It also can't be produced from decaying organic matter in a reasonably pure form on any sensible timescale. Lastly, we don't know exactly what humus is chemically
+Organic matter is decomposed by animals (for example earth worms) and microorganisms in the soil. Most of these soil microorganisms need oxygen and they always need water. They work faster in higher temperatures. This means that within regions of similar moisture conditions, the organic matter content of soil decreases from north to south.
-"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, micro-oragnisms would try harder to attack them, but since they don't, they aren't 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" gets 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.
+Tropical regions have very little or no humus in their soil. Along the Mississippi River, where soil moisture conditions remain rather similar from south to north, we might find 2 percent in Arkansas, 3 percent in Missouri and over 4 percent in Wisconsin. Hot desert soils have virtually no organic matter.<ref>[http://www.wilderness-survival.net/composting/maintaining-soil-humus Maintaining Soil Humus] Wilderness Survival</ref>
-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 (can't 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 can also be made by humans. An example are the [[Terra preta]] soils that were made by tribes and cultures that flourished in the Amazon before the Spaniards came.
-Humus or even soil organic matter in general isn't 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 to be synonymous with soil organic matter. This is the non-mineral portion of soil. So 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."
+== Definitions of humus ==
-"The definitional problem here is actually quite easy to resolve. It is the standard distinction between colloquial usage and scientific usage. Colloquially, if you add mature compost, or even immature compost, to soil, the resulting mix is humus. The same can be said of adding lemon juice to crushed sesame seeds, but that is a different story. When actually studying soil, however, it is important to make sure that everyone is on the same page with their definintions, and that those definitions offer enough destinctions with other terms to provide a useful purpose, or else why use them.
+[[File:Western Hemlock litter.JPG|200px|thumb|left|An environment where humus is formed]]
+"Humus is the excrement of soil animals, primarily earthworms, but including that of some other species that, like earthworms, are capable of combining partially decomposed organic matter and the excrement of other soil animals with clay to create stable soil crumbs resistant to further decomposition or consumption."<ref>[http://www.wilderness-survival.net/composting/making-humus Making Humus]</ref>
-To this end, soil scientists break up the components of soil into categories. The portion that is the stable organic component is then refered to as humus, the portion that it is sand, clay, and related particles is silicates, the OM that is still decaying is, surprisingly, decaying organic matter. A simple way to look at this from the scientists perspective is to think of potting mix made from 1/3 peat, 1/3 compost, 1/3 sand or perlite. Peat is pretty much in its final state. It may have been that way for thousands of years, and may continue to be. Peat is humus. The compost, even if mature, is still breaking down and supplying nutrients. It is the decaying OM. The sand is the silicates.
+"Humus is the stable, long lasting remnant of decaying organic material. It improves soil structure and increases water retention. It's nutritive qualities include trace elements and several important organic acids but do not include nitrogen or phosphorus."<ref name="GardenWeb">[http://faq.gardenweb.com/faq/lists/organic/2002121127011493.html What is the real difference between compost and humus?] GardenWeb</ref>
-Normal soil has these fractions mixed together to differing degrees, and to make up for local deficiencies in one or another based on the types of plants you are growing, you ammend your soil. The benefit of compost is thus two-fold. First, it has the immediate effect of adding nutrients and bacterial components that aid in soil conditioning. Second, as the seasons progress, it eventually converts to humus and increases your humus count. Thus compost, over several seasons, can often be used by itself for growing, but there are some exceptions. Cacti, for instance, will not appreciate a soil made exclusively from compost and its humic derivatives. Without significant silicates or their equivalent, they will die.
+"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, micro-organisms would try harder to attack them, but since they don't, they aren't 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" gets 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."<ref name="GardenWeb"/>
+[[File:Cumulus Clouds over Yellow Prairie2.jpg|200px|thumb|right|Prairies, or grassland in general, is an environment where much humus can be formed.]]
+"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 (can't 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."<ref name="GardenWeb"/><br clear="all"/>
-The distincion mentioned by Kelly between "organic" as used by science and "organic" as used by gardeners is another story, and a pet peeve of mine. The distinction stemmed from a long-ago disproven belief called vitalism that maintained that organic molecules, carbon compounded with other elements (just having carbon is NOT the sole criterion, else diamond would be considered organic and it is not, and so would CO2, which also isn't) HAD per se to be manufactured by living things, that organic molecules were somehow different from other chemicals by virtue of possessing a force vitae. This belief was utterly overthrown in 1828 when Friedrich Woehler published a brief paper describing the synthesis of the organic compound urea, formerly isolated from urine, from ammonium cyanate via: (NH4+)(-OHN) ---> O=C(NH2)2. This laid the ground work for the dismantling of the concept of vitalism in chemistry, but not in the popular mind, and the idea still permeates modern society and gardening lore. Chemisty then split into two branches, biochemistry, which studied the actual chemistry of life, and organic chemistry, which studied the properties and interactions of carbon compounds. When many people say "organic" they really mean "biologic". This sloppiness is important, as many highly toxic substances are "organic," and mistaken beliefs that organic compounds are safe, just because they are biological, is a natural by-product of clinging to vitalism.
+== Humic acid ==
+Humic acid<ref>[http://en.wikipedia.org/wiki/Humic_acid Humic acid - Wikipedia]</ref> is a principal component of humic substances. It is not a single acid but a complex mixture of many different acids. Humic acids can form complexes with ions that are commonly found in soils creating humic colloids.<ref>A colloid is a substance microscopically dispersed evenly throughout another substance. For example, milk is an emulsified colloid of liquid butterfat globules dispersed within a water-based solution.</ref>
-So, all that being said, here is a quick primer:
-Organic matter - stuff that came from biological sources (should be biological matter. Diamonds and graphite don't decompose!) This includes humus, mature compost, immature compost, freshly cut plants, live plants, etc.
-Humus - (soil science) that portion of the soil that has fully broken down and is thus stable. This stability is important because it allows you to remove it from consideration in a lot of investigations, and this is why soil sciences define it this way. This, incidentally, is also why its constituents have not been subjected to rigorous scientific investigation. It is not that it is somehow mysterious or has magical properties that elude investigation, it is just that it is only recently that anyone has really bothered to think about applying modern analytical techniques to this fraction of the soil. Contrary to common belief, a large number of its constituents ARE known. Their relative proportions vary from implementation to implementation, however, and thus no simple answer is really forthcoming as to "what humus is," as it is a dynamic mix of substances. humus - (colloquially) The organic portion of the soil (you can see how this definition has use for the gardener, but is too impercise for much usefulness in an investigation of soil properties.)
-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 orgainc 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, active generation of metabolic gasses. Primarily still in bacterial stage of decomposition.
-Mature Compost - compost that has decomposed to the point of maximal usefulness. Usually in the fungal/actinomycete stage.
-So all mature compost is organic matter, but not all organic matter is mature compost. If what you are after is soil conditinoing alone, then the terms humus and mature compost are all but interchangeable."
-FIELD:
-"One more important attribute of humus should be listed, in addition to improving soil structure (or texture) and water retention. 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."
-== Rain worms ==
 == See also ==
@@ Line 52: / Line 33: @@
 * [[Micro-organisms in the soil]]
 * [[Soil]]
+* [[Terra preta]]
 == References ==
@@ Line 57: / Line 39: @@
 == External links ==
+* [http://en.wikipedia.org/wiki/Humic_acid Humic acid] Wikipedia
 * [http://en.wikipedia.org/wiki/Humus Humus] Wikipedia
+* [http://www.wilderness-survival.net/composting/maintaining-soil-humus Maintaining soil humus]
+* [http://www.wilderness-survival.net/composting/making-humus Making Humus]
 * [http://agriinfo.in/default.aspx?page=topic&superid=5&topicid=137 Soil Humus] My Agriculture Information Bank
 * [http://faq.gardenweb.com/faq/lists/organic/2002121127011493.html What is the real difference between Compost and Humus?] GardenWeb
 === Videos ===
-		 		{{#ev:youtube|Y0M6dbOoewc|400|left| 		}}
+{{#widget:youtube|id=Y0M6dbOoewc}}
 <br clear="all" />