Soil Secrets: Humic Acids
Dr. Melendez, Soil Secrets, Courtesy Daved Yarrow December 2008
How Humic Acid is Created
Humus is the common name used by most of us and it’s a term that lumps the stable molecular acids called Humic acids together with the not fully decomposed soil organic residue that is broken down into parts too small to identify it’s origins. Together this conglomerate of Humic acids which are bio-chemicals and the polymorphic Soil Organic Matter define the presence and sustainability of a top soil. Soil Organic Matter has a calorie value and will rapidly decompose or cycle into Carbon dioxide while the Humic acids are not rapid cycling, have no calorie value and therefore will have a chemical half life measured in many decades if not centuries. The term ‘Humic substances’ is often used interchangeably with Humic acids which addresses the most essential and long lasting carbon bank of substances that has a true bio-chemical benefit to a Soil’s Terrestrial Biosphere. In nature the riches sources of these substances are found in a rich top soil, peat, lignite coal, and Leonardite and the Humate formations of NW New Mexico.
Leonardite, is a highly oxidized form of organic matter, and is technically a low rank coal between peat and sub-bituminous. It was formed during a time of ancient salt water inland seas while Humate was formed when that North Western region of New Mexico was thick in huge tropical carboniferous forests and fresh water inland swamps.
Humic acids have a definable molecular structure of which a fragment is illustrated below.
The Humic acids of soil are a product of soil chemistry of which the precursor to humus formation is protein. The Humic acids are not organic matter in the true since as they have a definable molecular structure and are no longer decomposing organic biomass such as rotting roots or compost. It can be said that the Humic acids are essential for a healthy and productive soil.
Part of the chemical structure of the Humic acids has been oxidized away providing broken bonds which create places on the molecules where micronutrient ions can be absorbed. The oxidized sites give the entire molecule a negative charge enabling it to absorb micronutrients. The organic structure of Humic acid is naturally oxidized, as shown by the asterisks, giving it a negative charge.
Positive ions, attracted to broken bonds at the site of the oxidation, create sites for micronutrients and micro-flora to attach.
How Humus (Humic Acids) Work
Clay Disaggregation: Clay particles normally lay together flat as shown, but having a negative charge will repelled each other. When Salt (Na+) is present in minor amounts, the clay platelets will collapse.
Soils clay content can become so dense and compact that they may resist plant rooting because they lack good porosity with aerobic conditions needed by plant roots. This may happen for one of two reasons:
First, the salt in the soil has neutralized the negative electrical charges which normally cause clay particles to repel each other.
Salt overload causes clay platelets to attract each other.
When an excessive amount of salt is present, it neutralizes the negative electrical charges that normally cause clay particles to repel each other. The platelets move closer together. This is called soil collapse, a condition seen in irrigated regions world wide, where soil salinity is a growing problem.
Clay compaction
The percentage of clay in the soil can be so high that the positive charge on the edge of a clay particle combines with the negative charge on the flat surface of another, forming a tight three-dimensional structure as shown in in this image.
When the percentage of clay in the soil is very high, and especially when an excessive amount of salt is present, the positive charge on the edge of a clay particle combines with the negative charge on the flat surface of another, forming a tight three dimensional structure.
Water Penetration is Enabled with the help of Humic acids (Humus)
Humic acid causes the clay particles to stand on end, allowing water penetration. It does this in two ways.
1. First, it segregates salts (positive ions) and removes them from the surface of the clay particle. This restores a negative charge to the clay platelets causing the clay platelets to repel each other, therefore loosening the soil structure.
2. Second, a carbon group on the Humic acid molecule (carboxyl group) bonds with the edge of the positively charged particles. This breaks the attractive force between the positive charge at the edge of a particle and the negative charge or the flat surface of another.
This action, called protective colloidal action, loosens soil, letting roots penetrate more easily.
Micronutrient exchange is improved with Humus (Humic acids) in the soil.
Humic acid is extremely important as a medium for transporting nutrients from the soil to the plant.
Humic acid picks up positive ions. Since the root's negative charge is greater than Humic acid's negative charge, scientists theorize that the micronutrients are taken up by a plant's root and absorbed by the plant's circulation system.
Since the root system is negatively charged, when the Humic acid moves close to the root, the root's negative charge exceeds the acid's negative charge. The micronutrients are released from the Humic acid molecule and enter the root membrane.
Water Sequestration
Positive ions are more easily absorbed by a plant's root.
Humic acid holds cations in a way they can be more easily absorbed by a plant's root, improving micronutrient transference to the plant's circulation system.
Humic acid slows water evaporation from soils. This is especially important in soils where clay is not present or in a low concentration, in arid areas, and in sandy soils without the capability to hold water.
In the presence of water, cations absorbed by Humic acid partially ionize and move a short distance away from the Humic acid oxidation sites. This restores part of the bonded ion's positive attractive force. Since water is a dipolar molecule and electrically neutral, the end of the molecule containing the oxygen atom loosely bonds to the ion. The hydrogen or negative end of the water molecule is partially neutralized, and as a result, increases the hydrogen end's positive attracting force. The oxygen (or negative) end of another water molecule bonds with the hydrogen end and this continues until the attractive force of the water molecule is dissipated. This is called surface tension!
Humic acids can save up to 30% on water
The polar nature of water molecules allows them to bond to each other in groups and is associated with the high surface tension of water. The polar nature of the water molecule has many implications. It causes water vapor at sufficient vapor pressure to depart from the ideal gas law because of dipole-dipole attractions. This can lead to condensation and phenomena like cloud formation, fog, the dew point, etc. It also has a great deal to do with the function of water as the solvent of life in biological systems.
This effect reduces the evaporation rate by about 30%. Humic acid can significantly reduce water evaporation and increase its use by plants in non-clay, arid, and sandy soils.
Note:
i have a large .pdf file with powerpoint slides of useful information about humus, humic acids & the soil food web by dr. michael melendrez of www.soilsecrets.com. very useful information to better understand how biochar affects soil structure and character.
the file is 3.4mb -- to large to send through yahoogroups. i will email the file to anyone interested.
pasted below is the text from 9 of the 25 slides.
unfortunately, dr. melendrez doesn't know much about biochar and its effects in soils, and has formed a negative preliminary judgment about biochar -- seeing it as competitive and redundant to the humic acids he knows and loves. i respect his work, since he has perfected humus-building methods and materials that work very well in the alkaline and saline soils of the american southwest.
dr. melendrez first used the descriptor "soil food web" in a research paper he prepared in 1976 -- long before dr. elaine ingham in oregon coined the phrase to describe her own theories and insights.
for a green & peaceful planet,
David Yarrow
Turtle EyeLand Sanctuary
44 Gilligan Rd, East Greenbush, NY 12061
cell: 518-881-6632
www.championtrees.org
www.OnondagaLakePeaceFestival.org
http://tech.groups.yahoo.com/group/carbon-negative
www.farmandfood.org
www.SeaAgri.com
