Along with most of the information needed to turn dirt into really good soil.
These are excerpts from a book I am working on, presented in "raw" form since the project is not yet ready for publication.
If you find this information helpful, I give permission (by virtue of it being put up on this site) to copy it for your own use.
all I ask is the respect of not putting my work up on any other site.
What we need to know about Soil
Consider a handful of soil. How does it appear to you, as dirt (a collection of minerals), or soil? At first glance it may appear very ordinary, something you routinely take for granted, it’s all the same isn’t it? However, once we make a closer inspection, we find that soil is far from ordinary, and certainly not dirt. It is the home of innumerable numbers of organisms, both easily visible and microscopic. Soil acts as Earth’s recycler, filter, purifier, and storehouse. The soil ecosystem recycles dead organisms into the building blocks of new life, it transforms toxic substances into simple compounds, it renders pathogenic organisms harmless, and it purifies and stores water as it passes through. Soil is a dynamic living system that functions as the interface between land and sky, the living and the dead. Soil is the repository of fertility and life on this planet. Even though the nature and properties of soil vary greatly by location, its role in the ecosystems and the ways in which it functions are basically constant from one place to another worldwide.
Soils perform five key functions in the global ecosystem. Soil serves as a:
1. medium for plant growth,
2. regulator of water supplies,
3. recycler of raw materials,
4. habitat for soil organisms, and
5. landscaping and engineering medium
The first important function: As an anchor for plant roots and as a water holding tank for needed moisture, soil provides a hospitable place for a plant to take root. Some of the soil properties affecting plant growth include: soil texture (coarse of fine), aggregate size, porosity, aeration (permeability), and water holding capacity. This is paramount for any of us that want to grow our own food(s). A soil that is fine in texture, has good permeability, containing a good amount of humus will hold a vast amount of water. Another important function of soil is to store and supply nutrients to plants. The ability to perform this function is referred to as soil fertility. The clay and organic matter (OM) content of a soil directly influence its fertility. Greater clay and OM content will generally lead to greater soil fertility.
The second important function: As rain or snow falls upon the land, the soil is there to absorb and store the moisture for later use. This creates a subsurface pool of available water for plants and soil organisms to live on between precipitation or irrigation events. When soils are very wet, near saturation, water moves downward through the soil profile unless it is drawn back towards the surface by evaporation and plant transpiration. The amount of water a soil can retain against the pull of gravity is called its water holding capacity (WHC). This property is close related to the number of very small micro-pores present in a soil due to the effects of capillarity action. The rate of water movement into the soil (infiltration) is influenced by; texture, physical condition (structure and tilth), along with the amount of vegetative cover on the soil surface. Coarse (sandy) soils allow rapid infiltration, but have less water storage ability, due to their generally large pore sizes. Fine textured soils have an abundance of micropores, allow them to retain a lot of water, but also causing a slow rate of water infiltration. Organic matter tends to increase the ability of all soils to retain water, and also increases infiltration rates of fine textured soils.
The third important function: Soil performs one of its greatest functions; Decomposition of dead plants, animals, and organisms by soil flora and fauna (e.g., bacteria, fungi, and insects) transforming their remains into simpler mineral forms, which are then utilized by other living plants, animals, and microorganisms in their creation of new living tissues and soil humus. Many factors influence the rate of decomposition of organic materials in soil. Major determinants of the rate of decomposition include the soil physical environment, and the chemical make-up of the decomposing materials. The activity levels of decomposing organisms are greatly impacted by the amount of water and oxygen present, and by the soil temperature. The chemical makeup of a material, especially the amount of the element nitrogen present in it, has a major impact on the ‘digestibility’ of any material by soil organisms. More nitrogen in the material will usually result in a faster rate of decomposition.
Through the processes of decomposition and humus formation, soils have the capacity to store great quantities of atmospheric carbon and essential plant nutrients. This biologically active carbon can remain in soil organic matter for decades or even centuries. This temporary storage of carbon in the organic matter of soils and biomass is termed carbon sequestration. Soil organic carbon has been identified as one of the major factors in maintaining the balance of the global carbon cycle. Land management practices that influence soil organic matter levels have been extensively studied, and are often cited as having the potential to impact the occurrence of global climate change.
The fourth important function: Soil is teeming with living organisms of varied size. Ranging from large, easily visible plant roots and animals, to very small mites and insects, to microorganisms (e.g. bacteria and fungi.) Microorganisms are the primary decomposers of the soil, they perform much of the work of transforming and recycling old, dead materials into the raw materials needed for growth of new plants and organisms. For instance; an earthworm in its burrow excretes its waste (middens) on the soil surface, once deposited there it is further broken down by bacteria and other soil organisms. Organic materials in soil are consumed and digested repeatedly by different organisms on their path to becoming humus.
Most living things on Earth require a few basic elements: air, food, water, and a place to live. The decomposers in soil have need of a suitable physical environment or ‘habitat’ to do their work. Water is necessary for the activities of all soil organisms, but they can exist in a dormant state for long periods when water is absent. Most living organisms are “aerobic” (requiring oxygen), including plant roots and microorganisms, however some have evolved to thrive when oxygen is absent (anaerobes). Greater soil porosity and a wide range of pore sizes (diameter) in the soil allows these organisms to “breathe” easier. Soil texture has a great influence on the available habitat for soil organisms. Finer soils have a greater number of small ’micro-pores’ that provide habitat for microorganisms like bacteria and fungi. In addition to the need for suitable habitat, all soil organisms require some type of organic material to use as an energy and carbon source, which is what they require as food. An abundant supply of fresh organic materials will ensure a robust population of soil organisms.
The fifth important function: Soils are the base material for roads, homes, buildings, and other structures set upon them, however, the physical properties of different soil types vary greatly. The properties of concern in engineering and construction applications include: bearing strength, compressibility, consistency, shear strength, and shrink-swell potential. These engineering variables are influenced by the most basic soil physical properties such as texture, structure, clay mineral type, and water content. Landscaping applications range in scale from bridge and roadway construction around highway interchanges to courtyards and greenspaces around commercial sites to the grading and lawns of residential housing developments. In all these instances, both the physical and ecological functions of soils must be considered. Exposure of soil at a construction site creates potential for soil erosion by water, wind, or both. Eroded soil pollutes waterways and causes sedimentation of ponds and reservoirs.
Much More will follow.
*edited to separate things for easier reading*
And a question. I have heard two people say recently that you can have too much organic matter. I have always thought the opposite. If you have time, could you expound on this?
Most compost is not "ideal" which allows for misshapen balances, causing collapse of soil building blocks.
If you are creating ideal compost, that is well balanced then it is nearly impossible to incorporate too much.
However, if the compost is out of balance (meaning acidic or basic with little of the good biosphere) then you can indeed have too much of a bad thing.
The other mistake is to use anaerobic compost as the main component, this tends to harbor far more "bad" microbes and their complment critters than "good" microbes and their complement critters resulting in an imbalanced soil system.
Ideal soil is in balance, poor soil is out of balance both chemically and biologically.
There is even a soil class, Histosol, that is primarily composed of organic materials, this soil class comprises a meager 1% of the total earth land surface area.
As I go along with this thread, each soil class will be explained.
I will be going over soil and what makes it first, then we will delve into the microbiology and macrobiology and end with what is needed to turn dirt into good soil.
Thanks for your replies James and Todd.
i have ascertained that bringing together the minerals
with the microbes is a big key to soil health.
(obviously, PH, structure, moisture are all very important)
but microbes transform minerals into a usable form.
iv e noticed this when i had some worm castings
VERY high in microbal life.
and i added diatomaceous earth to it.
DE is like a powder. the particles are very small
small enough to be directly transformed by the microbes.
adding these 2 together created a super mineral product
that made my plants take off.
perhaps they were hungry for silica ?
i dont know, but, i do know i had results
and thats the best answer i could come up with.
i also started adding red compost worms to my guilds.
i have several inches of compost, yard waste, leaves, coffee grounds
under my fruit trees.
i was giving them worm castings, and decided i had so many worms
i would just set some free
so, for a year, i added castings only removing %40 to %50 of the worms back to the bin
sometimes i got lazy, and didnt remove any, they all went under the fruit trees.
Now i have stable productive colonies of red compost worms
we had 1 night below freezing this winter (28F), but it didnt seem to bother them a bit.
i still have loads of them all over my yard.
they work 24x7 for me, and have yet to charge me once
I will be getting into the microbiology once I have finished with the basic soils.
Worm castings (middens) are indeed rich in bacteria but once deposited on the soil surface they are further broken down by other bacteria, protozoa, and others.
DE, food grade or otherwise is a source of calcium by virtue of the amorphous silicon dioxide exterior and small calcite interior, and that is one of the nutrients the microbiome of soil requires for food. (1 diatom skeleton is equal to around 100 bacteria in physical size).
Interestingly enough amorphous silicon dioxide is one of the components of human bone and is also needed by every living thing for life to occur. the silica also is one of the needed items for calcium uptake and use by every living thing.
Great trials and observations!
Thanks for your post.
*edited to clarify the DE and Calcium interaction*
2. This soil book, covering soil A to Z, hopefully to make it all understandable by anyone who might pickup the book and read it.
Thank you for bringing this up. I want to say this now that a few have brought items up. If you want me to delve into any part deeper, just say so here and I will cover all questions to the best of my ability.
step 1 - clear the area - see chapter one for various methods
step 2 - plant your cover crop - see chapter two for cover plants by season
step 3 - turn the cover crop into soil - chapter x for methods
Rather than read a 300 page book and trying to figure out what to do, I can look at a list that tells me how to get started, look over the information that pertains to that, and get out on my property and get started with SOMETHING, without worrying about what to do next, or whatever. I find it extremely motivating if I know exactly how to start, there is no confusion as to the order of things, and I have subsequent steps laid out for me.
Soil Quality, as a general concept, can be thought of as the ability of a soil to function, in either natural or managed ecosystems, to sustain plant and animal life, and maintain or enhance air and water quality.
For agricultural ecosystems, we may consider Soil Quality as the ability of a soil to produce safe and nutritious crops in a sustained manner over the long-term, without impairing the resource base or harming the environment.
Notice that this premise seems to be contrary to the currently accepted commercial agricultural model in the developed countries as well as those currently becoming developed countries.
Machinery use is one of the catch 22’s of the modern agricultural model.
Another is the relatively new “package” where seed is matched to herbicides and sold with discounts to entice farmers to purchase these products.
Soil Quality has the potential for many different interpretations.
Quality is dependent upon factors such as land use, soil management practices, ecosystem and environmental interactions, and the priorities of human societies.
When considering Soil Quality in any specific case, it is necessary to identify the major issues of concern with respect to that soil’s function.
Soil that is great for holding up buildings is not particularly good for raising any crops.
Whatever definition of the term Soil Quality is deemed appropriate for a specific use, it should relate to the capacity of the soil to function effectively with regard to productivity; environmental quality; and plant, animal, and human health now and in the future.
Since the majority of food and fiber needs of the human population are met by crops grown in managed agricultural ecosystems, the focus of government agencies is on those systems.
However, the basic principles presented should be applicable to soils in other ecosystems, both natural and managed.
Some soil properties can be relatively easy to observe, measure, and monitor over time:
Soil properties used as indicators of soil quality.
Texture and aggregation
Aeration and infiltration
Organic matter content
Acidity - alkalinity (pH)
Soil Respiration (CO2)
Major factors which lead to reductions in soil quality, land degradation, and soil erosion:
• Mismanagement: Lands that are improperly managed (e.g., improper tillage) lose their topsoil.
Either in large chunks during extreme erosive events, or little by little over an extended period of time, the soil disappears from the land resulting in reduced productivity and a degraded condition.
• Salinization: Results from the accumulation of salts in improperly irrigated soils, most frequently in arid regions.
• Overharvesting: Occurs on cultivated soils when repeated harvests are made from land without returning organic residues and mineral nutrients to the soil.
• Contamination: Exposure of soil to toxic substances, as a result of industrial processes or chemical spills, can severely damage the ability of a soil to perform its ecosystem function.
Cultural and environmental factors which enhance or degrade soil quality:
Soil Quality Enhancing
organic material additions
cool, humid climate
fibrous root systems of plants
minimal tillage operations
Soil Quality Degrading
hot, arid climate
For plant growth, the topsoil is the richest and most valuable part of the soil.
Topsoil formation is a very slow process (in nature, (we are developing methods that enhance the speed of natural topsoil production)), which makes it a non-renewable (within the current standard thinking), (but re-usable) resource in terms of human lifespans.
Keeping the soil in place while it is used for construction or crops is one of the greatest challenges faced by engineers and land managers.
Unfortunately the current engineering manifest does not take soil condition (other than what is best for their use) into account.
Soil erosion losses are greatest when the soil surface is exposed to intense rainfall, resulting in gulley formation.
Natural soil fertility is largely contained in the remains of formerly living things, also known as organic matter.
Continuous removal of plant material for food or forage leads to gradual depletion of natural soil fertility.
Soil properties can vary greatly from one location to the next, even within distances of a few meters.
These same soil properties can also exhibit similar characteristics over broad regional areas of like climate and vegetation.
The most general level of classification in the USDA system of Soil Taxonomy is the Soil Order.
All of the soils in the world can be assigned to one of 12 orders.
By surveying soil properties of color, texture, and structure; thickness of horizons; parent materials; drainage characteristics; and landscape position, soil scientists have mapped and classified nearly the entire contiguous United States and much of the rest of the world.
Soil Orders and General Descriptions
Entisols Little, if any horizon development
Inceptisols Beginning of horizon development
Aridisols Soils located in arid climates
Mollisols Soft, grassland soils
Alfisols Deciduous forest soils
Spodosols Acidic, coniferous forest soils
Ultisols Extensively weathered soils
Oxisols Extremely weathered, tropical soils
Gelisols Soils containing permafrost
Histosols Soils formed in organic material
Andisols Soil formed in volcanic material
Vertisols Shrinking and swelling clay soils
Descriptions of the 12 soil orders
Entisols are a very diverse group of soils with one thing in common, little profile (horizon) development.
Includes the soils of unstable environments, such as floodplains, sand dunes, or those found on steep slopes.
Entisols are commonly found at the site of recently deposited materials (e.g., alluvium), or in parent materials resistant to weathering (e.g. sand).
Entisol soils also occur in areas where a very dry or cold climate limits soil profile development.
Productivity potential of entisols varies widely, from very productive alluvial soils found on floodplains, to low fertility/productivity soils found on steep slopes or in sandy areas.
Aridisols are dry soils with CaCO3 (lime) accumulations, common in desert regions.
The extent of aridisol occurrence throughout the world is widespread, second in total ice-free land area only to the entisols.
Extensive areas of aridisols occur in the major deserts of the world, as well as in southwestern north america , Australia , and many Middle Eastern locations.
Aridisols are commonly light in color, and low in organic matter content. Lime and salt accumulations are common in the subsurface horizons.
Some Aridisols have an argillic (clay accumulation) B horizon, likely formed during a period with a wetter climate.
Water deficiency is the dominant characteristic of Aridisols with adequate moisture for plant growth present for no more than 90 days at a time.
Crops cannot be grown in these soils without irrigation. Productivity of Aridisols is generally low, and there is potential for land degradation due to overgrazing by livestock.
If irrigation water is available, Aridisols can be made productive through use of fertilizers and proper management.
Alfisols are found in cool to hot humid areas, and in the semiarid tropics; they are formed mostly under forest vegetation, but also under grass savanna.
Extensive areas of alfisols are found in the Mississippi and Ohio River valleys in the USA, through Central and Northern Europe into Russia, and in the South-central region of South America.
Alfisols generally show extensive profile development, with distinct argillic (clay) accumulations in the subsoil.
Extensive leaching often produces a light-colored E horizon below the topsoil.
Generally fertile and productive, these soils typically have a high concentration of nutrient cations (Ca, Mg, K, and Na) and form in regions with sufficient moisture for plants for at least part of the year.
Natural fertility and productive capacity of alfisols is considered to be greater than that of ultisols, but less than that of mollisols.
Ultisols are intensely weathered soils of warm and humid climates.
They are typically formed on older geologic locations in parent material that is already extensively weathered.
Ultisols have accumulated clay minerals in the B horizon.
While generally low in natural fertility (basic cations, Ca2+, Mg2+, and K+) and high in soil acidity (H+, Al3+) the clay content of ultisols gives them a nutrient retention capacity greater than that of oxisols, but less than alfisols or mollisols.
Large areas of ultisol are found in the southeastern USA, China, Indonesia, South America, and equatorial regions of Africa.
Gelisols are soils with permafrost within 2 meters of the surface.
These soils generally have limited profile development.
Most of the soil forming processes in these soils occur near the surface, sometimes resulting in significant accumulation of organic matter.
Large areas of this soil occur in the Northern regions of Russia, Canada, and Alaska.
These areas become boggy wetlands in the summer, and support large numbers of migratory birds and grazing mammals.
The permafrost of gelisols tends to become unstable (melt) if disturbed, leading to a waterlogged soil condition that poses problems for engineering uses.
Andisols soils form in volcanic ash and cinders near or downwind from volcanic activity.
Generally lacking in development, they are not extensively weathered, forming in deposits from geologically recent events.
Usually of high natural fertility, they tend to accumulate organic matter readily and are of a ‘light’ nature (low bulk density) that is easily tilled.
These soils generally have a high productivity potential.
Inceptisols are soils in the beginning stages of soil profile development.
The differences between horizons (layers) are just beginning to appear.
Some color changes may be evident between the emerging horizons, and the beginnings of a B horizon may be seen with the accumulation of small amounts of clay, salts, and organic material.
These soils show more profile development than entisols, but have not developed the horizons or properties that characterize other soil orders.
Inceptisols are commonly found throughout the world, and are prominent in mountainous regions.
The natural productivity of these soils varies widely, and is dependent upon clay and organic matter content, and other edaphic (plant-related) factors.
Mollisols take their name from the Latin word mollis, meaning soft.
These mineral soils have developed on grasslands, vegetation that has extensive fibrous root systems.
The topsoil of mollisols is characteristically dark and rich with organic matter, giving it a lot of natural fertility.
These soils are typically well saturated with basic cations (Ca2+, Mg2+, Na+, and K+) that are essential plant nutrients.
These characteristics of mollisols place them among the most fertile soils found on Earth. Found in North America from Texas up to Saskatchewan, Canada.
Spodosols commonly form in sandy parent materials under coniferous forest vegetation.
As a consequence of their coarse texture, they have a high leaching potential.
Spodosols are characterized by high acidity, and have a subsoil accumulation of organic matter, along with aluminum and iron oxides, called a spodic horizon.
Typically low in natural fertility (basic cations, Ca2+, Mg2+, and K+) and high in soil acidity (H+, Al3+), these soils require extensive inputs of lime and fertilizers to be agriculturally productive.
Spodosols are most commonly associated with a cool and wet climate, but also occur in warmer climes such as in Florida, USA. Large areas of spodosol are found in northern Europe, Russia, and northeastern North America.
Oxisols are the most weathered of the 12 soil orders in the USDA soil classification system.
They are composed of the most highly weathered tropical and subtropical soils, and are formed in hot, humid climates that receive a lot of rainfall.
Oxisols are located primarily in equatorial regions.
These soils are extensively leached, and the clay size particles are dominated by oxides of iron and aluminum, which are low in natural fertility (Ca2+, Mg2+, K+) and high in soil acidity (H+, Al3+).
While oxisols are typically physically stable, with low shrink-swell properties and good erosion resistance, these soils require extensive inputs of lime and fertilizers to be agriculturally productive.
Histosols are soils without permafrost that are predominately composed of organic materials in various stages of decomposition.
They generally consist of at least half organic materials (by volume).
They are usually saturated with water which creates anaerobic conditions and causes organic matter accumulation at rates faster than that of decomposition.
Little soil profile development is present, due to their saturated and anaerobic condition, however layering of organic materials is common.
Histosols can form in wetland areas of any climate where plants can grow such as bogs, marshes, and swamps, but are most commonly formed in cool climates.
Vertisols are soils with a high content of clay minerals that shrink and swell as they change water content.
The clay minerals adsorb water and increase in volume (swell) when wet and then shrink as they dry, forming large, deep cracks.
Surface materials fall into these cracks and are incorporated into the lower horizons when the soil becomes wet again.
As this process is repeated, the soil experiences a mixing of surface materials into the subsoil that promotes a more uniform soil profile.
Vertisols are usually very dark in color, with widely variable organic matter content (1 – 6%).
They typically form in Ca and Mg rich materials such as limestone, basalt, or in areas of topographic depressions that collect these elements leached from uplands.
Vertisols are most commonly formed in warm, sub-humid or semi-arid climates, where the natural vegetation is predominantly grass, savanna, open forest, or desert shrub.
Large areas of vertisols are found in Northeastern Africa, India, and Australia, with smaller areas scattered worldwide.
There are color maps available online to see the Soil Orders by continent, just do a search for "Soil Orders by Continent"
I'll get more of this posted as I have time.
You’ve started a good thread, Redhawk. Thanks.
I’ve been organic gardening on one scale or another for most of my life, so it’s over 25 years now. I use cover/green-manure cropping, compost, mulching, etc. Our basic soil, on an uphill bench, not bottom land, is not really considered “good” by ordinary standards. The mineral portion under the topsoil is sand in most areas, or sand and silt (virtual absence of clay-size particles) in a few.
Even though we've been building up topsoil for years, it’s exhilerating to see the difference that spreading a layer (say, inch-and-a-half thick) of well rotted cattle manure can make in a vegetable patch. We’ve also identified situations where there’s been a deficiency of one or more essential plant nutrients – for instance, magnesium or potassium – and when corrected, this has made an unmistakable improvement.
So in your opening post I thought you probably avoided specifically going into the subsoil mineral content for a good reason, as possibly you wanted to avoid the simple and disastrously incomplete understanding of “soil” that prevails in conventional modern farming. Which is “dirt” with selected chemicals added into it.
But I thought I’d bring the element topic up. Besides the well-known concern with “N P K” (which, granted, can be a misguided obsession) there are other elements such as calcium, sulphur, zinc, copper, iron, boron, manganese, molybdenum and more that play roles in plant development, disease resistance, animal and/or human nutrition, etc. I strongly believe in the amazing conditions and ‘natural provision’ of healthy soil life, as you’ve outlined. Yet totally closed ag systems are very challenging to achieve. Cropping for food, fiber, etc does tend to remove nutrients (molecules) from the soil.
Other discussions here on Permies.com have mentioned plant guilding or intercropping to help supply one type of plant with nutrients stored or exuded in the soil by one or more other plants. I’m sure there is practical worth in that. Another idea has been put forward that seems less proven to me, on the basis of my experience: at least one person has suggested plants can obtain from soil, or even foliar-feed themselves, nutrient elements suspended in the air. I’m sure I’m leaving out mention of other ideas.
But anyhow, since we know the texture and content of the mineral soil on different acreages can vary, what are your basic thoughts on this, from a practical standpoint? In terms of what a given soil can offer the plants we intend to grow. Am I jumping the gun here? (You may have intended to provide background before getting into what I've asked about. And probably the books you’re writing will go into depth on this, but since you've started this thread to discuss generalities, I thought I’d ask a general question.)
Todd Parr wrote:Redhawk, I can tell you one thing I would like to see in any book I read that pertains to vast, complex subjects like this. Somewhere at the end, have a summary that is a step-by-step overview to accomplishing the task so the information isn't overwhelming. I would love to see it broken down into simple broad steps, like:
step 1 - clear the area - see chapter one for various methods
step 2 - plant your cover crop - see chapter two for cover plants by season
step 3 - turn the cover crop into soil - chapter x for methods
Rather than read a 300 page book and trying to figure out what to do, I can look at a list that tells me how to get started, look over the information that pertains to that, and get out on my property and get started with SOMETHING, without worrying about what to do next, or whatever. I find it extremely motivating if I know exactly how to start, there is no confusion as to the order of things, and I have subsequent steps laid out for me.
I am impressed Todd, you must be channeling or connected to the spirits since you have had the premonition of where we will end this thread.
Right now is the base knowledge needed for understanding your land, then we will go step by step to the end goal of making what you have to work with the best it can be.
If one has the monetary means, any plot of land can become nearly perfect soil, the question is not can you but are you willing to. I've spent a lot of the last 40 years helping or trying to help commercial farmers do what is best for all concerned.
As I go along in this thread we will get to the stage of discussing methods that work, why they work and how long they work.
I will also answer questions and probably raise some questions.
Bryant RedHawk wrote:hau Joel, this thread should have some missing links for your knowledge, it just will take me some time to get everything posted. I am going in hopefully a logical order, if you don't know what you are starting with how are you going to improve it correctly?
Yes, good point. I realize now how you planned to develop this thread... and I did jump the gun, there. Sorry.
By the way, my forester friends long ago tole me we have a spodosol here (called a "podzol" in Canadian terminology).
If you want to slow the migration of water through the spodosol then you will be making additions of clays and other finer particles, these will change the structure which will allow for more water holding capability.
Of course this is just the first step, since there are biological needs for the best and highest amount of water retention abilities. We will be going over that in the second section of this thread.
Soil Science is a chemical study of dirt, it is not about soil but rather about the base components needed for dirt to be ready to become soil.
There is a problem with the way most people use soil science.
Most people that want to start gardens or farms or any type of growing of plants will be advised “get a soil test” it will tell you what you need to add to grow great plants.
When you take your samples of your land to the lab and they give you your analysis report.
There is no mention of the biology that sample contained, only the mineral components, perhaps the particle size break down will be included in a “complete” soil analysis you will also get “micronutrient” lists.
The report will also tell you what to do to get that point we call “normal” but it will again only be mineral additions, pH adjustment amendments and perhaps particle size amendment, all based on what is considered to be “normal, friable, land”.
Nothing about anything biological that needs to be added will be mentioned. Why is this?
It is because then we would not be soil scientist we would be biologist or microbiologist.
See the problem here?
Soil is Living, Dirt is Inert.
In this thread we are going to gain knowledge about the mineral parts of land.
Then we are going to gain knowledge about the living part and how these parts go together to create the medium that all life is dependent on for life, that we call soil.
Then we are going to learn some methods for getting that hunk of land we call our own to become the best soil it can be for what we want to grow.
Given that land usually contains decent amounts of the right minerals, fair pH range, good enough particle size distribution, enough organic matter to hold good amounts of water.
The real issue becomes how to get those minerals into a form that the plants can actually use.
This is not the focus of Soil Science, even though the name indicates otherwise.
This is the goal of this thread, to get all the information needed to arrive at the perfect or as perfect as possible soil condition and health for optimal plant growth.
While having good soil can seem to be complicated, (it can be very much so) it can also be very manageable with the right knowledge.
Perhaps the most important things in this thread will be ways you can determine, on site, what you need to do and how to best accomplish this yourself.
Sure you can use your plants to tell you, but that means that by the time they are showing you something is wrong, it is too late for that crop.
I consider the most important tool for people doing what we are doing to be a microscope, without one you will never know what life your soil contains nor how much of that life your soil contains.
Interestingly enough, that soil life will tell you more than all the comprehensive soil tests you ever have done can tell you. Why is this?
Because most likely your land already has the quantities of minerals (at least for the most part) that what you want to grow need to be there.
Without the right soil biota present we are not being the good steward for those plants we want to thrive, nor are we making the best use of most of the water we manage to store in the land.
The goal here is to disperse that knowledge needed to have gardens that even in draught periods of a year or more will produce at least a decent amount of food.
I will end this thread with some step by step methods, along with tests for making sure you are heading to that wonderful place called great soil.
This thread is a generous gift of your time and expertise. Thank you.
I am certainly following along.
So now we know there are 12 classes of soil we call the soil order and how they differ.
Obviously we need to know how much of the earth each of these classes occupy.
Entisols = 16% of the world land area or 21 million km squared.
Aridisols = 12% or 15.7 million km sq.
Alfisols = 10% or 13.1 million km sq.
Ultisols = 8 % or 10.5 million km sq.
Gelisols = 9% or 11.8 million km sq.
Andisols = 1% or 1.3 million km sq.
Inceptisols = 17% or 22.3 million km sq.
Mollisols = 7% or 7 million km sq.
Spodosols = 9.2% or 4 million km sq.
Oxisols = 8% or 8 million km sq.
Histosols = 1% or 1.3 million km sq.
Vertisols = 2% or 2.6 million km sq.
Others = 5% or 6.6 million km sq.
Total = 100 % or 131 million km sq.
Much of the land mass of earth, according to the soil orders is not suitable for agriculture use.
As Permaculture practitioners we know that much more land can be utilized for agriculture use, even if in smaller patches than one thousand acres (mean size of current commercial agriculture farms).
You see, soil science only takes into account the perameters deemed significant by chemistry, it does not take into account the Biology factors in any way, shape or form.
It also doesn't take into account that soil types can be improved to the point of becoming very fertile, water holding, nutrient rich soils.
Biome is a term used to classify the Earth’s major ecosystems.
A biome is defined primarily by the climate and predominant vegetation of a region.
The flora and fauna present within a specific Biome reflects the adaptations of those organisms to that particular environment.
The Major World Biomes map is based upon the underlying properties of soil moisture and temperature regimes - which are largely determined by latitude, climate, topography, and the native vegetation that has adapted to these local conditions.
The nature and extent of soil formation and development is closely associated with these local and regional conditions.
Inferences about the active soil forming processes, the type and extent of rock and mineral weathering occurring at a particular location may be drawn from the knowledge of the biome location.
Influence of native vegetation on the quantity, type, and distribution of organic materials in the soil, and of the organisms that live in the soil can be drawn from the Biome classification.
Basic Characteristics of World Biomes
• Tundra – Cold soil temperatures, with permafrost. Occurs at high latitudes (>60 degrees) and altitudes (alpine).
• Boreal – a climate of short summers and harsh winters. Mainly coniferous vegetation.
• Temperate – mid-latitude zones ranging from ~ 40 to 65 degrees, deciduous forest vegetation where precipitation is sufficient (>750 mm).
• Mediterranean – occur in latitudes from 30 to 45 degrees. Mild, wet winters, warm-hot dry summers.
• Desert – arid climate with low precipitation (< 250 mm/year) and high evaporation.
• Tropical – refers to latitudes from ~ 5 to 35 degrees. Warm temperatures year-round, with distinct wet and dry seasons (e.g. Monsoons).
• Humid – a climate where average annual precipitation exceeds the amount of evaporation.
• Semi-Arid – Average precipitation of 250 to 500 mm annually.
• Permafrost – a layer of soil that remains frozen year-round.
Interestingly, there are currently permaculture sites, growing good food in all but the Tundra and Permafrost Biome zones.
So, this too is a subjective set of perameters that don't apply absolutely as soil science dictates.
The ability of the land to perform its function of sustainable agriculture production and enable it to respond to sustainable land management. This is true, but if you rely on artificial amendments how is that sustainable?
Class 1 is the class with the most desirable quality and class 9 is the class with the poorest quality.
The ability of the land to revert to a near original production level after it is degraded, as by mismanagement. (The end result of mismanagement is erosion, so how does land that has gone missing revert?)
Land with low soil resilience is permanently damaged by degradation.
The ability of the land to produce (measured by yield of grain, or biomass) under moderate levels of inputs in the form of conservation technology, fertilizers, pest and disease control.
Land with low soil performance is generally not suitable for agriculture.
Note here that Soil Science considers "moderate" use of Fertilizers, pesticides and herbicides (disease control) Ok.
The problem with this thinking is that it has been shown, in many studies, that application of chemical (synthetic) fertilizers, pesticides and herbicides poison the soil and are fatal to all the microbiome that makes dirt soil.
What they are saying is that it's ok to turn good soil into dirt, then give it chemically measureable fertility that completely wipes out everything that was soil producing.
This is the precise reason I left the USDA.
There can be no food security under these premises and it certainly can't be sustainable agriculture.
What we need is to find the "Happy Median", that magic place where we install any missing mineral components in the correct amounts, build up the microbiome so that all those good minerals can be made available to the things we want to plant.
In other words, we need to build Soil, not re-enforce Dirt.
The last few years I performed soil tests, I included a microbiology battery and included everything in the results report.
I was written up on at least ten occasions because I was not following protocols set by Washington. When I recommended mineral supplementation the quantities were far smaller than called for. That is because there is no need to use mass quantities of any minerals nor of Nitrogen, Phosphorus or Potassium, too much and you are actually doing far more harm than not making any amendments in the first place. What most soil tests tell us to do is drown our plants and kill off the microbiome, substituting artificial, chemicals for real soil nutrition.
This is one of the main reasons that foods you buy in the grocery store have very little tastes, it is also one of the big reasons we are becoming a sick people with diseases on the rise ever since the end of the Dust Bowl era.
In the next installment we will begin our biological journey and start learning just exactly what "Soil" is and more importantly, how to make sure we are building the best soil we can.
I'm planning some soil surveys later for my property to determine how well ponds would hold water in different areas.
I have also found well logs to be very useful to get an overall picture of what a sites soil profile is. It is just a snapshot but it can still be very useful.
Thank you for touching on the mineral piece of this. I'll keep coming back to learn more. I'm curious about application rates of minerals and your thoughts on fostering the soil life to get good results in the garden. I've been working toward this goal in my garden for a long time. I've had mixed results in the past, but things keep getting better every year.
I, too, would express my appreciation for your good efforts. Threads like this can and do achieve a certain epic status in the archival honeycomb of the internet, so be prepared when strangers want to take selfies with you.
I hope to learn more how soil or its components handle mineralizing toxic elements or heavy metals. Being elemental, I would not expect metals to be destroyed. Perhaps "transmuted" might be a real expectation of mine, and understanding the implications surrounding biosolids and my ultisol world would be a real interest. I developed the surely unoriginal idea that mercury remains in coal precisely because of biodrome activity after reading Dr Inghams works and watching videos that represented her points, as well as Jeff Lowenfels talks. The bug has bitten me, so please, carry on.
Why we should all eat a little DE for a complete, nutritional diet.
In 1939, the Nobel Prize winner for chemistry, Professor Adolf Butenant, demonstrated that existence is not possible without the presence of Silica.
Based on his research carried out at Columbia College in 1972, silica is a vital nutrient that should be provided continuously from food sources.
Silica plays a huge role in lots of body functions and it has an immediate relationship with mineral absorption.
The typical human body holds roughly seven grams of silica, a sum far exceeding the figures for other important minerals, for example iron.
Both iron and silica are essential for the human body, meaning they're required for undertaking ongoing metabolic work that's vital to existence.
Both elements should be continuously provided.
Many studies prove the favorable influence of vegetal silica taking place on the development of animals and humans.
Silica is important to the skeleton and mineralization. Hence, silica’s absence leads to skeletal and penile deformation.
Hormonal disturbances within the human organism are frequently because of a calcium- magnesium discrepancy.
Several researches have proven that silica can restore this delicate balance.
Silica also benefits the assimilation of phosphorous.
As a result it may be described as a catalyst in using additional factors.
Brittle bones are really a characteristic of aging.
As calcium within our body leaches, the bones become brittle and weak.
Taking merely calcium mineral cannot correct or stop this threatening and crippling disease since the human body cannot assimilate and take advantage from the calcium, without the existence of silica.
Evidence indicates that, rather than affecting healing, supplemental mineral calcium, on the other hand, speeds up the draining away of bone calcium and thus hastens the degenerative procedure for brittle bones and other alike illnesses affecting the encouraging and connective tissue in the body.
For brittle bones, silica can help stop the discomfort, as well as restore your body’s self-repair process.
Calcium and Silica
Brittle bones’ signs and symptoms attack women mainly after menopause, however the degenerative process begins much earlier within their more youthful days.
More women are dying of fractures triggered by brittle bones than of breast cancers, cervix, and uterus combined.
In brittle bones, loss from the bones happens because of inadequate manufacture of the encompassing protein medium in which calcium salts first deposit.
Deficiencies in calcium within the bone matrix result in enlargement of waterways and spaces within the bones, giving these a porous, thinned appearance.
The destabilized bone becomes fragile and might be damaged at any kind of minor injury.
The bones might even fracture from normal pressure or stress.
To intent to re-mineralize broken bones, it's suggested that the silica supplement is taken daily.
Bones comprise mainly phosphorus, magnesium and calcium they also contain silica.
Silica accounts for the adding of minerals in to the bones, especially calcium.
It boosts the healing of fractures as well as reduces skin damage to begin of the fracture.
Increasingly more research evidence implies that via a transmutation process, silica is converted into calcium when it's needed.
That's why some researchers make reference to silica like a precursor of calcium. Even if calcium is inadequate, the body can change silica into calcium if the bones need it.
These same interrelations exist in plants and other animals, so it is a needed mineral for a complete biological nutrient regime.
The easiest way for us to get silica into the soil for our plants is to use DE, it is also an easy way to get silica into our bodies.
When we make compost, we can easily add DE to the mix as we create our heaps, we can also simply spread it over the garden area prior to planting and at anytime during the growing season.
Hans, I also appreciate the answers you give in the threads I read here on permies. I was interested in having a plant source rich in silica and so internet-searched your suggestion of Horsetail rush. What I discovered was while it definitely is a good silica source, it had some potential toxin problems, including nicotine and thiaminase, see Plants for a Future at PFAF and also check the work of herbal formulator James Sloane regarding Horsetail Grass. A couple of my medical conditions precluded using Horsetail rush for me.
While Horsetail rush will be a plant I put on my wish list as a fiber plant (scouring pans, etc.); silica-rich edible bamboo shoots could also be a potential choice for eating...although, according to guaduabamboo.com, bamboo has heavy-duty toxins as well. Even when boiled, apparently pregnant women should not eat bamboo shoots, see Homeremedieslog.com.
Obviously, I am no expert on any of these plants, but I thought you and others might appreciate what an internet search came up with. And, of course, each of us has a unique body with differing levels of tolerance to the foods we ingest...figure out what is best for you before you bite.
Thank you again. Much respect to you.
We just added a second buried wood bed. We dug down about 18 or so inches, put in rotten and rotting boards (layed in with their edges down, like a loaf of sliced bread). The extracted dirt was sifted through 1/4" hardware cloth, returned and smoothed over perfectly, like the top of a cake. It is void of anything that could hold water, feed microbes, earthworms, nothing to create air space and water easily rolls off the top. I protested, but the H insisted it be done this way. We also sifted some of the remaining dirt onto the older bed and removed some of its chunky top mulch. It had been doing pretty well until now.
We planted spinach seeds in the newly added dirt on the older bed and in 3 other locations (including my BTE bed and another spot I recently amended). The birds found the spinach and still attached seeds in the buried wood bed and plucked out a good number of plants. The plants that remain are tiny, weak and far behind those in the other locations. The H thinks it has only to do with the cold snap we had.
I can't get the H to understand the difference between dirt and soil! I have been using our evening walks to nonchalantly talk about soil in general. Last evening he said, "Again with the microbes? Do you have to keep mentioning the microbes?"
Yesterday I asked him if I could add some composted wood chips to the bed. He said, "I just sifted all that out and you want to put it back? It has rotten wood underneath." And that's helping the spinach how?!
We plan on replanting the bed with something else, but when he asks what would I like there I just feel like crying. He'd never care to read anything on a forum, so... I can't wait til you have your book published Bryant!
Another enlightening episode from you and I would like add myself to the list of people thanking you.
Thanks. That all sounds reasonable, but I am dealing with an unreasonable soul here.
I tried again this evening with my soil sermon. It was met with great opposition as we planted onions into the "dead bed".
I took him by the hand over to the pile of well decomposed wood chips (on the other side of the yard). I broke a chunk open to show him what looks like vanilla pudding inside the chunk and told him how happy the microbes would be to have that. How moist it was. Fuel for fungal friends. Blah, blah, blah.
He patronizes by saying, "What you say makes sense, but..." Or "It's all about experimenting with what may work." I believe that there are some things that I am SURE of. I've experimented enough already. I see what doesn't work.
Might I ask what brought him to his conclusions about how to best grow plants?
If he were to read just about anything about growing plants he would find that almost all published literature mentions compost being a good amendment and that mulch at the least helps to retain water where you want it.
From what you have said, I am very confused about where he came up with his notions about gardening.
If he feels he must read books to learn, then I highly recommend Elaine Ingham's book "Building Soil Health". She also has great articles located on the USDA web site. If you mate recognizes the USDA as a good source of knowledge, then those articles will enlighten him.
The book is coming along fairly well, last week was full of other commitments but I should be available here for the rest of this week. Feel free to pm.
I really don't know what leads to his thinking here. I give him every permaculture book I own to read and every issue of MEN and Organic Life. I don't yet own a book that covers only soil building, structure and health. I know yours will be a good one. I wish you much luck on its compilation. Now I'm going back to reread everything you've written here. Thank you.
Plants obtain nutrients from two natural sources: organic matter and minerals, the plants use exudates (phyto to call out to the microorganisms and primary beneficial predator organisms for what they need at that time in the way of nutrients.
Organic matter includes any plant or animal material that returns to the soil and goes through the decomposition process.
Decomposition is actually microorganisms eating the organic materials and minerals, these then become food for larger organisms, so the microorganisms are the bottom of the food chain.
In addition to providing nutrients and habitat to organisms living in the soil, organic matter also binds soil particles into aggregates and improves the water holding capacity of soil.
Most soils contain 2–10 percent organic matter. However, even in small amounts, organic matter is very important, without organic materials there can be no soil.
Soil is a living, dynamic ecosystem. Healthy soil is teeming with microscopic and larger organisms that perform many vital functions including converting dead and decaying matter as well as minerals to plant nutrients.
Different soil organisms feed on different organic substrates. Their biological activity depends on the organic matter supply.
Nutrient exchanges between organic matter, water and soil are essential to soil fertility and need to be maintained for sustainable production purposes.
Where the soil is exploited for crop production without restoring the organic matter and nutrient contents and maintaining a good structure, the nutrient cycles are broken, soil fertility declines and the balance in the agro-ecosystem is destroyed.
Soil microorganisms are the most abundant of all the biota in soil and responsible for driving nutrient and organic matter cycling, soil fertility, soil restoration, plant health and ecosystem primary production.
Beneficial microorganisms include those that create symbiotic associations with plant roots (rhizobia, mycorrhizal fungi, actinomycetes and diazotrophic bacteria),
promote nutrient mineralization and availability (protozoa, nematodes and flagellates), produce plant growth hormones, and are antagonists of plant pests, parasites or diseases (biocontrol agents).
Many of these organisms are naturally present in the soil, although in many situations it may be beneficial to increase their populations by inoculation or by applying various management techniques that enhance their abundance and activity.
Mycorrhizae: We now know that more than 90% of the world’s plants are mycorrhizal, with varying degrees of dependence and benefits derived from this association.
The best known and perhaps the most common mycorrhizal symbioses involve arbuscular mycorrhizae (many crop species), ectomycorrhizae and endomycorrhizae (only woody species; mostly tree and shrub species), although several other types (e.g., Ericaceous, Orchidaceous, Ectendo-mycorrhizae) also exist.
The positive role of mycorrhizae in plant production is well documented, with many cases of growth and yield enhancement, particularly in highly dependent, susceptible plants.
The plant response can be due to various reasons, although in most cases it is due to an increase in effective root area for water and nutrient extraction, since the mycorrhizal hyphal network works as a natural extension of the plant root system.
The plant donates carbon to the mycorrhizae in exchange for a greater ability to use native soil resources.
Other benefits of the mycorrhizal association are an enhanced protection against pathogens, improved tolerance of pollutants and greater resistence to water stress, high soil temperature, adverse soil pH and transplant “shock.”
The wide-spread use of mycorrhizal inoculants in agroecosystems has been hampered by the difficulties of cultivating arbuscular mycorrhizae.
This hampers our ability to produce quantities that are sufficient for broad application of the inoculate at affodable prices.
This cost per quantity problem makes the most practical current use of mycorrhizae to be in land restoration and reclamation efforts, along with arbuscular and ecto-mycorrhizal inoculation of tree and crop seedlings in nurseries.
Even with production economics being what they are, enhancement of naturally occurring mycorrhizal populations in agricultural fields (and their potential benefits to the growing crops) is feasible and important benefits can be realized through the adoption of management practices that enhance mycorrhizal populations and activities such as reduced tillage, crop rotations and lower N and P applications.
Rhizobia. (The Nitrogen Fixers):
The role of the six genera of the Rhizobiaceae bacterial family in agricultural production has also been well documented.
Rhizobia infect plant roots, once in place they get busy creating nodules where N2 is fixed, providing the plant with most of the Nitrogen it needs for its development.
Well nodulated plants can form an efficient symbiosis allowing them to fix up to 250 lbs. of Nitrogen yearly.
Some of this N is added to the soil during plant growth by ‘leaky’ roots, though most remains in plant tissues and is released during decomposition, to the benefit of the following crops or the intercrop.
It should be noted that nitrogen fixing bacteria are adversely affected by large additions of Nitrogen Fertilizers, it will even shut them down or kill the bacteria.
Since nitrogen fixing plants only get their N from the soil and mostly through the active nodules, it is advisable to not fertilize or to fertilize at a low rate (no more than 10 lbs. per acre).
It has also been found that the presence of silica is needed for proper utilization of several nutrients including nitrogen in the plant preferred form of NH3.
Previous colonization of the legume roots by mycorrhizae may greatly enhance nodulation by rhizobia, ultimately increasing the potential growth benefits.
Despite the obvious benefits of rhizobial inoculation or management, several factors continue to limit the wide-spread use of this technique to enhance legume yields.
Current practices that are actually working against better yields include: Use of Nitrogen rich fertilizers, Lack of incentives to grow legumes, Environmental constraints (particularly edaphic; e.g., low P-status), Difficulty in producing inoculate and its consequent low availability, Low genetic compatibility of the host legume with the bacteria (low effectiveness), and lack of appropriate political and economic incentives and infra-structure.
There are several methods available to enhance nitrogen fixation:
1. host plant selection (breeding legumes for enhanced nitrogen fixation)
2. selection of effective, compatable strains able to fix more nitrogen
3. use of agronomic methods that improve soil conditions for plant and microbial symbiont
4. methods of inoculation application
It is best to utilize several of these methods to insure best results, no one is particularly better than another so combining techniques is a good hedge for success.
Some legumes are better at fixing nitrogen than others.
Common beans are poor fixers (less than 50 lbs. per acre) and fix less than their nitrogen needs.
Maximum economic yield for beans in New Mexico requires an additional 30-50 lbs. of fertilizer nitrogen per acre.
However, if beans are not nodulated, yields often remain low, regardless of the amount of nitrogen applied.
Nodules apparently (in this particular case) help the plant use fertilizer nitrogen efficiently.
Other grain legumes such as peanuts, cowpeas, soybeans, and broad beans are good nitrogen fixers, and will fix all of their nitrogen needs other than that absorbed from the soil.
These legumes may fix up to 250 lbs. of nitrogen per acre and are not usually fertilized.
In fact, they usually don't respond to nitrogen fertilizer as long as they are capable of fixing nitrogen.
Nitrogen fertilizer is applied at planting to these legumes when grown on sandy or low organic matter soils to supply nitrogen to the plant before nitrogen fixation starts.
If nitrogen is applied, the rate is low, 10 lbs. per acre being the norm.
When large amounts of nitrogen are applied, the plant literally slows or shuts down the nitrogen fixation process.
It is easier and less energy consuming for the plant to absorb nitrogen from the soil than to fix it from the air.
Perennial and forage legumes such as alfalfa, sweetclover, true clovers, and vetches may fix 250-500 lbs. of nitrogen per acre.
Like the grain legumes previously discussed, they are not normally fertilized with nitrogen.
They occasionally respond to nitrogen fertilizer at planting or immediately after a cutting when the photosynthate supply is too low for adequate nitrogen fixation.
In all cases, the more the plants can utilize the nodules the better for the plant.
Nodules that are working well will be pink or red in color, inactive nodules will be green, gray or white.
Plants may even drop inactive nodules.
When we harvest the crop we are removing much of the nitrogen, but by turning under the plant leaves, stems and roots and allowing these to rot, incorporating the matter back into the soil, we can return all the nitrogen left in the plants.
Another benefit is that the active bacteria present in that crops nodules is returned to be available for the next crop planted for sustainability.
Additional symbiotic N2 fixing relationships of plants with microbes include actinomycete (Frankia) relationships with mostly trees and shrubs (and some standard crops such as sorghum), and symbiosis between endophytic, diazotrophic bacteria (e.g., Azotobacter, Azospirillum, Acetobacter, Azoarcus, Burkholderia, Herbaspirillum) and grasses. The Frankia symbiosis is generally exploited in land reclamation and restoration efforts using principally Casuarinas trees to hold soil (e.g., sand dunes) in place but its potential is still underutilized.
On the other hand, research on and use of endophytic bacteria have been well developed in tropical regions, particularly Brazil and Mexico.
These bacteria not only fix N2 but also modify the shape and increase the number of root hairs, helping the plants to acquire more nutrients.
The application of these organisms in inoculants continues to be performed on a wide-scale (mostly in maize, some in rice, wheat, sugar-cane and rice), and yield increases ranging from negligible up to almost 100% have resulted, depending on the crop and bacteria used.
Various other beneficial rhizosphere organisms titled as plant growth promoting bacteria (PGPB) have been used primarily as seed inoculants.
PGPB affect plant growth through direct growth promotion (hormonal effects), induced systemic resistance to diseases, mineralization, substrate competition, niche exclusion, detoxification of surrounding soil and production of antibiotics, chitinases (filamentous fungi helper biopolymer), cyanide and siderophores (Iron chelating compounds).
Several bacterial species and genera have been used as plant growth promoters, including pseudomonads (e.g., Pseudomonas fluorescens, P. putida, P. gladioli), bacili (e.g., Bacilus subtilis, B. cereus, B. circulans) and others (e.g., Serratia marcescens, Flavobacterium spp., Alcaligenes sp., Agrobacterium radiobacter). Probably the most successful have been Agrobacterium radiobacter, used to control crown gall on several plant families.
Bacilus subtilus to suppress Rhizoctonia solani (cereal root rots) infection, and various inoculants (mostly Bacilus-based) termed YIB (yield improving bacteria), used widely throughout China on vegetable crops.
The main limitation to greater use of these techniques is the poor understanding of the interactions between PGPB and the host plant and interactions with the indigenous soil microflora.
Improved understanding of these phenomena will permit a more accurate prediction of the effects of inoculation and its potential benefits.
Even though this is a small part of what goes on in soil, it is important to have an understanding of just how each of the component parts works so we can then understand what they do for us, the grower of plants.
When a plant needs a particular nutrient it puts off a particular exudate that signals the bacteria and other microorganisms that handle that particular nutrient to make it available to the plant.
So this brings us to the question “what is an exudate?” Plant roots are the gatherers and bacteria, fungi hyphae are the providers, waiting for the plant to tell them what the current need(s) are.
Root exudates are a complex mix of organic acid anions, sugars, phytosiderophores, purines, nucleosides, vitamins, gases (CO2 and H2), enzymes, inorganic ions such as HCO3-, OH- and H+ and root border cells.
This concoction is to bacteria and fungal hyphae what cookies, cakes, pie and ice cream, and chocolate are to humans.
These exudates have major direct or indirect effects on the acquisition of mineral nutrients, vitamins and all the other building blocks plants need to grow strong, healthy and large.
Phenolic and aldonic acids exuded directly by roots of N2-fixing legumes serve as major signals to Rhizobiaceae bacteria which form root nodules where N2 is reduced to ammonia.
Some of the same compounds affect development of mycorrhizal fungi that are crucial for phosphate uptake.
Plants growing in low-nutrient environments also employ root exudates in ways other than as symbiotic signals to soil microbes involved in nutrient procurement.
Extracellular enzymes release P from organic compounds, and several types of molecules increase iron availability through chelation.
Organic acids from root exudates can solubilize unavailable soil Ca, Fe and Al phosphates.
Plants growing on nitrate generally maintain electronic neutrality by releasing an excess of anions, including hydroxyl ions.
Legumes, which can grow well without nitrate through the benefits of N2 reduction in the root nodules, must release a net excess of protons.
These protons can markedly lower rhizosphere pH and decrease the availability of some mineral nutrients as well as the effective functioning of some soil bacteria, such as the rhizobial bacteria themselves.
Thus, environments which are naturally very acidic can pose a challenge to nutrient acquisition by plant roots, and threaten the survival of many beneficial microbes including the roots themselves.
To be continued.
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