Bio-Organo-Mineral Complex
Contents
Introduction
Soil microbiologists originally viewed the soil as the environment in which soil microbes develop. As the science of soil microbiology advanced, it was revealed that a soil's environment is the result of the activities of the soil micro-organisms within it; that is to say, they create the soil environment.
Soil scientists have come to realize that without a basic understanding of a soil's microflora and microbial action, it is difficult to resolve either theoretical or practical soil problems such as:
Releasing nutrients from the soil to the growing crops.
Balancing or increasing a soil's natural fertility.
Recommending applications of materials or products to a soil.
It has become increasingly important to understand the characteristics, activities, and requirements of the soil micro-organisms as well as to grasp the existence of dynamic soil-life activity within a fertile soil.
Since soil microbes play such an important role in creating fertile soil, their role is essential in the Bio-Organo-Mineral Complex.
A soil is divided into:The active (living) portion.
The inert (static) portion.
Soil microbes live and function in a solution within the soil. This soil solution forms a coating around the soil particles and fills the spaces between them. The lower the nutrient level within the solution, the slower the development, reproduction, and activities of the microbes. An adequate supply of life sustaining oxygen is also a requirement for many useful soil microbes. Therefore, a favorable soil texture (tilth) greatly aids in the activity and reproduction of these microbes.
The Active Portion
The active portion of the soil is where the B-O-M Complex occurs. In simplest terms, it is comprises:
The soil microflora
The organic and inorganic colloidal substances
The soil solution
Soil gases
All of these components are in constant action and interaction.
This B-O-M Complex activity in a soil will determine the soil's qualities, characteristics and fertility. One measurement of the active portion's intensity is the presence of organic nitrogen; the inert portion does not contain nitrogen. The natural level of nitrogen in a soil is directly affected by the activity of living organisms.
Static-dynamic soils are divided as follows:
Acidic (podzol soils)
Mixed (black soils)
Alkaline (brown soils and gray desert soils)
The individual soil types differ one from another by:
The degree of saturation of absorptive capacity
The composition of nitrogen substances
The ratio of carbon to nitrogen, and
The biological properties.
The Bio-Organo-Mineral Complex must be understood as a "complex" system consisting of many "simpler" systems which are localized and jointly perform the mineralization processes and the synthesis of organic substances. The following four major systems occur within the total Bio-Organo-Mineral Complex:
This system forms active microzones around the residues of plant and animal proteins within the soil. It is best characterized by the "zymogenous" microflora.
System II
This system develops additional microzones in soils which contain other organic matter (non-protein) and is characterized by the "autochthonous microflora A" which consists mainly of cocci and fungi. The result of this activity is the formation of the alfa-humates. It is this system that delivers increased organic matter levels to the soil.
System III
This is the "Key" system that creates a fertile soil and is where the microbes perform their most important functions. It is characterized by a high level of "autochthonous microflora B" which is the most desirable for a naturally fertile soil. This system forms even more microzones that finalize the decomposition process and vigorously pursues the essential mineralization process. It is in this system that the following biological functions occur:
- The essential plant nutrients are converted and released to the growing crop.
- Microbes are fixing nitrogen from the atmosphere.
- Nitrification microbes oxidize nitrogen within the soil.
- Microbes decompose cellulose.
- Microbes decompose humates.
- Microbes mineralize organic compounds of phosphorus.
These are but the major biological functions occurring among many in this system.
System IV
This system forms other microzones with the stable calcium humates (beta-humates); however, the microbial activity is very weak in this system due to the lack of nitrogen.
The first system occurs in all types of soils.
Acidic soils have a strongly developed second system, a very weak third system, and no fourth system. Liming and good cultivation practices with acidic soils will produce a favorable improvement in their Bio-Organo-Mineral-Complex that results in development of "autochthonous microflora B" and ß-Humates (systems III and IV).
It is the second and third systems that provide a continuous supply of nutrients to growing crops and truly represent a soil's natural fertility. When these systems are weak or non-functioning, the soil is "sick" and will not produce top quality or high yielding crops.
These four individual systems of the Bio-Organo-Mineral Complex are stages of mineralization and humification of organic substances. These systems must be understood as a "dynamic process" which is gradually ever changing.
The Inert Portion
From the inert portion of the soil, the sorbents affect the Bio-Organo-Mineral Complex. Among the inorganic sorbents, clay minerals are the most important as they contribute to the germination and the activities of the soil microbes by enlarging the active surface of the substratum. They are the source of cation exchange capacity and also improve soil structure.
When all the essential nutrients are present in the soil, clay minerals can affect the development of soil microorganisms; the smaller or finer these clay particles, the more they increase this activity.
Although the earth's crust is a tremendous mass approximately seven miles thick, only an extremely thin layer is fertile topsoil. All survival of life on earth depends on this comparatively thin layer of topsoil, teeming with its legions of essential microbes.
Topsoil, the skin on the earth's crust is a product of weathering, an aging process associated with physical, chemical and biological activity. The original sediments and soil features are continuously being modified by this process, resulting in a complex of mineral types.
The dominant substances subjected to weathering are sand, silt and clay. Of these, clay is perhaps the most difficult to visualize because its aluminosilicate particles are the smallest, being of microscopic size (less than 2µm diameter).
The most useful classification of soil is based on its content of sand, silt, and clay. At one extreme we have pure sand and at the other, pure clay. Most soils are mixtures that fall between these extremes.
The amount of clay in a soil is most important in determining its degree of fertility. Clay appears in the form of minute crystals which have a markedly cracked surface. Clumps of these crystals are held together with humus and extracellular polysaccharides produced by certain micro-organisms (mostly fungi) forming granules or aggregates. This clumping together is responsible for good tilth, the granular structure of fertile soil, which is so sought after by perceptive farmers.
Soil particle distribution according to international norm considers clay to be <0.002 mm (79 millionth of an inch), silt as 0.002-0.02, fine sand as 0.02-0.2 mm, coarse sand as 0.2-2.0 mm and particles >2.0 mm are considered gravel. There are other systems for classification, such as the USDA system, but they commonly agree on the clay size as being <0.002 mm. While not all particles <2µm exhibit clay properties as defined in mineralogy, but most of them do.
The formation of clay begins as weathering of rocks. Temperatures, rain, chemical, and biological degradations of rock minerals are the starting processes of clay formation. In the presence of organic acids the formation of clay is significantly increased. Besides the formation of clay minerals these processes also lead to the formation of oxides and hydroxides of minerals.
Mostly crystals of feldspar (also olivine, augite, etc.) are the starting minerals for clay formation. They are broken up in the weathering process into oxides, hydroxides, alumina, and silica. Water leaches the hydroxides away and clay is formed by combining mostly alumina and silica to form clay mineral crystals. Clays also contain iron and magnesium in various amounts depending on the type (clays do contain a vast variety of elements in various quantities, not just the ones mentioned here). Clays are not the end product of weathering, rather they persist for long periods of time in soils due to their resistance to degradation. The formation is also a chain where one clay is formed in time from another (like kaolinite may be formed from montmorillonite).
Clays are predominantly aluminosilicates (contain mostly aluminum and silicon), but other clay structures are also known. Such are minerals with the properties of aluminosilicate clays which do not contain silicon (hematite, gibbsite). At this time we are mostly concerned with the aluminosilicate clays.
Four different clay types are differentiated based on their layering structure:
The amorphous clays (allophane) have no discernible crystalline structure. They are predominant in young volcanic soils. Allophane has high water holding capacity and will transform into crystalline clays in time.
The dimorphic clays (1:1 clays) are based on one silica and one aluminum sheet (Al is sometimes substituted partly or mostly by Mg and/or Fe); the sheets are held together by oxygen bonds. These two sheets act as one layer. Different clays in this group exist (kaolinite, nacrite, halloysite, and more), which are differentiated on the basis of their iron and magnesium content, or by water association (in halloysite).
The trimorphic clays (2:1 clays) have two sheets of silica and between them one sheet of alumina. Many trimorphic clays exist and differentiation may be done based on several factors (such as occupation of the centers of the octahedra, or on their properties). The trimorphic clays are the most important of all the types of clays for micro-organisms in the soils.
Here differentiation based on expandability of the layers is essential as it also separates the clays into the most useful (expanding clays like montmorillonite) and less useful (nonexpanding clays like illite) to micro life.
The tetramorphic clays (2:1:1 clays) are just like the trimorphic clays but a fourth sheet is attached to one of the outer silica sheets. The fourth sheet may be of aluminum, iron, or a magnesium hydroxide octahedral. These clays have typically a low expandability.
As mentioned, besides the aluminosilicate clays there are also oxide, and hydroxide clays. They are made of either silica, iron, aluminum, or manganese oxides and/or hydroxides hydrated or non-hydrated.
Both clay and humus are significant to the soil due to their large area per weight (in montmorillonite the internal area may reach 800m2/g) and due to their charges.
Humic compounds are negatively charged (pH dependent) due to carboxyl (COOH) and hydroxyl (OH) groupings; which provide pH buffer capacity and space for accepting other atoms (minerals) or molecules (organics) by accepting or giving up protons (H+).
Two main reasons for charges on AlSi-clays are that one ion may substitute another that is similar in size but different in charge thereby creating a charged part, or due to their hydroxyl grouping. AlSi-clays have negative and positive parts intermixed and are dependent on pH. Oxide and hydroxide clays are mostly positively charged in low pH, and negatively charged in high pH soils.
Yet humus (per weight) has several times more ion exchange capacity than clay, is more interacting with its surrounding, and minerals bound by humus are more easily released. In addition, humus contains micropores for soil gases (like oxygen), but clays have micropores that are significantly less supportive of microorganisms.
Both humus and clays are not the end products of decomposition; they resist and decompose slowly. Humus is the organic and clay is the mineral part of what is called stable humus.
