Soil Information Thread

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The physical properties of a soil influence its ability to support plant growth, cycle nutrients, hold water, act as an environmental filter or even support a building. Soil physical properties are dictated by the type and arrangement of soil particles. Lets discuss some of the basic physical properties of soil....

Composition of the Soil

A soil is a three-dimensional natural body comprised of solids, liquid, and gas that occurs on the land surface. In general, soil consists of approximately 45% mineral material, 5% (or less) organic matter and 50% pore space (which is occupied by air and/or water). The proportion of air and water that comprise a soil changes based on variations in rainfall, temperature, and other aspects of the climate.

The mineral fraction of the soil is made up of particles that fall into three different size classes: sand (0.05 – 2.0 mm diameter), silt (0.002 – 0.05 mm), and clay (<0.002 mm). The terms sand, silt, and clay only describe the absolute size of the soil particles, not what minerals make up the soil particles. As the size of the particles decrease, their influence on nutrient and water holding capacity increases. Smaller particles have more surface area available for interaction with nutrients and water molecules.

To illustrate the concept of surface area, picture a Rubik's Cube® game. When assembled, the cube has six faces, each of which is 3 inches wide x 3 inches long. Therefore, each face has a surface area of 9 square inches, for a total surface area of 54 square inches. The total outside surface area of the Rubik's Cube® would be analogous to the surface area of a large sand particle.

Because very few people ever solve the puzzle, it inevitably gets disassembled into 27 cubes that each have six faces, each of which is 1 inch wide x 1 inch long. Therefore, each face has a surface area of 1 square inch for a total surface area of 6 square inches. Since there are 27 of these small cubes in each Rubik's Cube®, there is a total of 162 square inches of surface area. This would be analogous to the surface area provided by 27 single clay particles (small cubes), which in this case would be the same size as one sand particle (large assembled cube).



Soil Texture and Textural Classes

Soil texture is the relative proportion of sand, silt and clay particles in the soil. In general, soils dominated by sand-sized particles are coarse-textured or sandy soils, soils dominated by silt-sized particles are moderate-textured or loamy soils, and soils dominated by clay-sized particles are fine-textured or clayey soils.

Soils can be further grouped into twelve soil textural classes based on the proportion of sand, silt and clay as defined by use of the soil textural triangle (Figure 1). Soil textural class can be determined in the laboratory or estimated by a trained soil scientist using a "feel" method in the field.

Knowledge of the soil texture can provide clues about other important soil properties, such as water holding capacity and fertility. For example, sandy soils are often well drained with low fertility, organic matter and water holding capacity.


Figure 1. The soil textural triangle is used to categorize soils based on the proportion of sand, silt, and clay sized particles.

Loam

is soil composed of sand, silt, and clay in relatively even concentration (about 40-40-20% concentration respectively). These proportions can vary to a degree however, and result in different types of loam soils: sandy loam, silty loam, clay loam, sandy clay loam, silty clay loam, and loam. Loam soils generally contain more nutrients, moisture and humus than sandy soils, have better drainage and infiltration of water and air than silty soils, and are easier to till than clay soils. The different types of loam soils each have slightly different characteristics, with some draining liquids more efficiently than others.
Loam is considered ideal for gardening and agricultural uses because it retains nutrients well and retains water while still allowing excess water to drain away. A soil dominated by one or two of the three particle size groups can behave like loam if it has a strong granular structure, promoted by a high content of organic matter. However, a soil that meets the textural definition of loam can lose its characteristic desirable qualities when it is compacted, depleted of organic matter, or has clay dispersed throughout its fine-earth fraction.

http://edis.ifas.ufl.edu/mg451

 

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Soil Structure

In the soil, particles can be held together in groups called aggregates (also called peds). These soil aggregates, and how they occur in the soil profile, determine the soil structure. Soil structure impacts the ability of a soil to transmit and store air, water and nutrients. Soil aggregates form in the soil as a result of physical and chemical processes. Soil organic matter acts as a binding agent for soil particles, which promotes particle aggregation and hence, good soil structure.

The types of soil aggregates are granular, platy, blocky, prismatic and columnar. Some soils do not have visible soil structure and are considered to be structureless. There are two types of structureless soils, single-grain and massive. Soil aggregates rarely form in these soils, even when there is adequate soil organic matter.




Soil Density

The solid (mineral and organic) particles that make up a soil have specific particle density, which is defined as the mass of solid particles in a unit volume. The particle density of a soil is not affected by particle size or arrangement; rather it depends on the type of solid particles present in the soils. Mineral soil particles have a higher particle density than organic matter because mineral particles are much heavier on a unit volume basis. The average particle density of a mineral surface soil is about 2.65 grams per cm3 (which is equivalent to 165 pounds per cubic foot!).

Soil bulk density is the mass of dry soil per unit volume. Unlike the measurement of particle density, the bulk density measurement accounts for the spaces between the soil particles (pore space) as well as the soil solids. Soils with a high proportion of pore space have low bulk densities and vice versa. Sandy soils with low organic matter tend to have higher bulk density than clayey or loamy soils. Soil bulk density is usually higher in subsurface soils than in surface horizons, in part due to compaction by the weight of the surface soil.

Soil management can impact soil bulk density. For example, driving heavy equipment over the soil during construction or agricultural production can compact the soil and increase the bulk density. When soils reach high bulk densities, root penetration and water infiltration can be reduced. Trying to grow plants in soils with high bulk density is essentially the same as trying to grow them in a brick or rock.

 

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Soil Pores and Water

As mentioned earlier, the portion of the soil volume occupied by air and water is called pore space. The amount of pore space is determined by the arrangement of the soil particles. The amount of pore space is low when soil particles are very close together, such as in compacted soils. The amount of pore space is higher when soils have high organic matter and the soil particles are arranged into soil aggregates (i.e., good soil structure).

Sandy soils normally have 35-50% pore space, while medium to fine-textured soils have 40-60% pore space, or more in cases of high organic matter and granulated structure. Pore space decreases with soil depth.
The ability of the soil to hold and transmit water and air is impacted by the amount of pore space in the soil and by the size (diameter) of those soil pores. Soil pores can be classified into two main groups depending on the diameter of the individual pore. Macropores are large diameter pores (≥ 0.1 mm) and micropores are small diameter pores (< 0.1 mm). Coarse-textured soils contain a large proportion of macropores, while fine-textured soils tend to have a high proportion of micropores.

Under normal conditions, soil micropores are usually filled with water, while macropores are filled with air. However the amount of air or water in the pore spaces will be impacted by several factors. For example, precipitation and irrigation events add water to soil pores, while drainage, evaporation or plant uptake remove water from soil pores. Because water is removed easiest from macropores, they will be the first to empty. Therefore, coarse-textured soils are drought sensitive because they do not have the ability to hold a sufficient amount of water for optimum plant growth. In contrast, the movement of water and air through micropores is very slow. Therefore, it is important for fine-textured soils to have good soil structure, otherwise the amount of air (oxygen in particular) in the pores may not be sufficient to support root growth.

Summary

Natural surface soils consist of approximately 45% mineral material, 5% (or less) organic matter, 50% air or water filled pore space. The proportion of sand, silt, and clay particles in the soil determines soil texture. When soil particles are held together in soil aggregates, the soil has structure. Soils with no visible aggregates are structureless.

The type of particles that comprise the soil dictate the particle density, which is relatively constant for mineral soils. Bulk density of soils accounts for the soil particles and pore space per unit volume. Soils have a combination of large macropores that transmit air and water easily, and micropores that tend to be filled with water. These soil physical properties influence water, air, and nutrient movement, which impact plant growth.

 

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Potting Mixes for Certified Organic Production

Potting Mixes for Certified Organic Production

Organic production of seedlings, transplants, and potted plants requires the use of media that meet the requirements of the National Organic Standard. This publication lists commercial sources and provides formulas and guidance for on-farm preparation of approved media... https://attra.ncat.org/attra-pub/viewhtml.php?id=47


Farms and nurseries use various seedling and potting media in the production of field transplants, container plants, and greenhouse crops. Such media may contain a wide range of natural and synthetic materials. In certified organic production, there are limitations on the materials that may be used, either as base substrates or for supplemental fertilization. This publication will help organic producers find commercial sources of organic potting media — or make their own...

Commercial Blends

Organic producers who choose not to mix their own growing media either purchase pre-packaged mixes or arrange with manufacturers to have a mix custom-blended for them. The latter option is occasionally chosen by large growers and by groups of growers who pool their orders to save money. Some enterprising growers order more than they need and sell potting media as a sideline.

For those who buy off-the-shelf, finding appropriate growing media can be a challenge. Until recently, the market for organic seedling and potting media has been small, and few commercial blends have been readily available. Also, due to occasional changes in requirements of the national Organic Standard, acceptability of products may change somewhat over time. The Washington State Department of Agriculture’s organic program also reviews and lists allowed products. Their product listing can be viewed on the Organic Food Program website.

One good indication that a commercial product is acceptable in organic production is a label stating that the product is "OMRI Listed." OMRI — the Organic Materials Review Institute (1) — is a nonprofit entity that evaluates products and processes for the organic industry. OMRI Listed products have been thoroughly reviewed and are consistent with the requirements of the National Organic Standard.
However, to be absolutely certain that a product is acceptable for organic use, read the label to learn the ingredients. If any components of the mix are questionable, check with your certification agent before buying it. This publication discusses many of the ingredients allowed in organic production, as well as those that are prohibited — or at least suspect.

To help you locate commercial sources of growing media and some of the main ingredients, there is a list of commercial sources in Appendix 1. This list was assembled in the spring of 2001 and updated in 2010. Since company ownership, media formulations, and available products can change with time, you should ask questions to make sure you are getting an organically approved product...


Making Your Own

All good potting media should meet the needs of plant roots for air, water, nutrients, and support. These needs will vary, however, depending on the plant and its stage of growth. The technical details are beyond the scope of this publication and can be found in standard horticultural literature and publications distributed by the Cooperative Extension Service. A list of several information resources about growing media is in Appendix 2. Some of these focus on organic systems; others address conventional production but contain basic and/or relevant information. Anyone who wants to produce consistent, high-quality growing media should study and do detailed research.

Working from tried-and-true recipes is a good idea, especially at the beginning. Appendix 3 features several recipes for organic media blends. Some of these recipes are found in published literature; others are from conference and workshop handouts or notes with uncertain authorship. Experimentation is the only sure way of knowing which blend or blends will work best for a particular farm or crop.
When experimenting, begin by making small batches and give them a thorough evaluation. The next step is largely logistical: assembling the components and equipment and finding space and labor for the mixing and storage. Storage can present its own challenges, especially preventing contamination by weed seeds.

Contrary to what some critics say, organic growers are permitted to use a wide array of materials in growing media. The challenge is more a matter of ensuring consistent quality of ingredients than in finding enough of them. The section that follows features a brief description of some of the materials commonly used in organic growing media and discusses some of the issues that surround them.

 

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Ingredients Allowed in Organic Potting Media

Ingredients Allowed in Organic Potting Media

Soil. For many years, the trend in conventional growing has been toward soilless media. A major reason for this is concern about soil-borne plant diseases and the excessive density of mixes where soil is a dominant ingredient. However, soil is still used in some organic blends.
Clean commercial topsoil is an acceptable natural ingredient, but you have to be certain that it has not been treated with prohibited ingredients to kill microbes and weed seeds.
Check the label or ask the supplier to be sure. If you are using soil from a farm or garden, use only the best. Consider solarizing, steam pasteurization, or oven heating if the soil has any history of soil-borne diseases. Microwaving is effective for pasteurization, but some certifiers might not allow it. Soil contaminated with pesticides, prohibited fertilizers, or environmental pollutants may not be used. Certifiers might require that any soil used must come from land in certified organic production.
Sand. Sand in a growing mix can make a difference. Coarse sand — called builder's sand — is best. It adds air spaces to the potting mix. Avoid plaster sand and other fine sands. They tend to settle into the spaces between the other ingredients and make a dense mix. Clean, washed sand has a near-neutral pH and little if any food value for plants. Sand is much heavier than any other ingredient used in potting mixes. The added weight is good for tall, top-heavy plants that might blow or tip over, but it is not the best choice for plants that will be shipped or moved a lot. Sand is the least expensive and most readily available larger-particle material.
Compost. Compost is perhaps the most common potting-mix ingredient among organic producers. Cheaper than traditional components such as peat moss, compost holds water well, provides nutrients, and can be made right on the farm.
The quality of compost depends in part on how it is made, but especially on what it is made from. The variability of commercial compost is one of the main reasons it is less common in commercial organic media. Lack of availability is also a common problem.
Experienced compost makers know that compost quality is directly affected by the raw ingredients. If the feedstocks are low in nutrients, the resulting compost will also be nutrient-poor. To produce a high-quality, media-grade compost, it is a good idea to make it according to a recipe — using a specific blend of balanced ingredients — rather than simply using whatever feedstocks come to hand. The end product will be more consistent and better-suited for blending with peat and other components.
According to one source (2), premium compost for nursery mixes should have:

• pH of 6.5 to 8.0
• no (or only a trace of) sulfides
• <0.05 ppm (parts per million) ammonia
• 0.2 to 3.0 ppm ammonium
• <1 ppm nitrites
• <300 ppm nitrates
• <1% CO2
• moisture content of 30 to 35%
• >25% organic matter
• <3 mmhos/cm soluble salts

When making compost for media, plan at least six months in advance of when it will be needed. For spring transplants, compost should be made the previous summer and allowed to age through the fall and winter. Composting is not difficult, but it does require some experience and a variety of clean, organically acceptable components. Animal manures and bedding, farm and garden waste, grass and alfalfa hay, and other materials can be combined to make a high-quality, reasonably consistent compost. Organic amendments such as greensand and rock phosphate can be added during the composting process to increase nutrient content. Protein-rich sources such as alfalfa and seed meals can also be included, if additional nitrogen is needed. While most compost will provide adequate amounts of phosphate, potash, and the necessary micronutrients, nitrogen has proved to be the most variable element and the most important to manage.
Compost is rarely used alone as a potting medium. Most compost is too porous and the soluble salt levels are often high. Rynk (3) recommends 20 to 30% compost content in potting mixes. Growers may use up to 50% in mixes for larger vegetable transplants (4).
In many circumstances, compost can suppress plant disease. Israeli researchers discovered that vegetable and herb seedlings raised in a mix of 40% vermiculite, 30% peat moss, and 30% composted cow manure grew faster, with less incidence of disease, than those raised in a 40% vermiculite/60% peat moss mix (5). To understand how compost suppresses disease, it is helpful to know how plant substances are broken down during the composting process. Compost goes through three phases. During the first phase, temperatures rise to 104 to 122 degrees Fahrenheit and materials that degrade easily are broken down. In the second phase, temperatures are between 104 and 149 degrees Fahrenheit, and substances like cellulose are destroyed. Also destroyed in this phase are plant pathogens and weed seeds, and (unfortunately) some beneficial biological- control organisms are also suppressed. The third stage is the curing phase, when temperatures begin to fall. It is during this phase that humus content increases and some beneficial organisms — like Streptomyces, Gliocladium, and Trichoderma, which serve as biocontrol agents — re-colonize the compost (6). This re-colonization is somewhat random. For example, composts produced in the open near a forest are more consistently suppressive than those produced in enclosed facilities. The reason appears to be the abundance of microbial species found in the natural environment (7).

 

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Ingredients Allowed in Organic Potting Media

Ingredients Allowed in Organic Potting Media

Composted pine bark. Composted pine bark has a high lignin content, making it slow to degrade. Bark lightens the mix, increases air space, and decreases water-holding capacity. It may be substituted, in part, for peat moss. Rynk specifically recommends it as a component in blends for potted herbaceous and woody ornamentals (3). Composted pine bark appears to impart some disease resistance (10). Its pH is generally 5.0 to 6.5, and it is low in soluble salts. Mixes using composted pine bark will probably require more nitrogen supplementation.

Sphagnum peat moss and other forms of peat. Sphagnum peat moss is the most commonly used soilless medium, because it is widely available and relatively inexpensive. Peat moss is a very stable organic material that holds a great deal of water and air and does not decompose quickly. Peat moss is quite acidic (pH 3.5 to 4.0); limestone is commonly added to the mix to balance the pH. Younger, lighter-colored peat moss does a better job of providing air space than older, darker peat that has few large pores.

Organic growers should be cautious when purchasing peat moss. A few commercial sources may be treated with wetting agents. Since all but a very few of the commercial wetting agents are prohibited in organic production, assume that any product with an unspecified wetting agent is prohibited. A few suppliers of untreated peat moss are listed in Appendix 2.

Other forms of peat can be used in growing media, though not all are readily found in the marketplace. Sphagnum peat moss — discussed here — is the most common peat and represents its least-decomposed form. Light, dark, and black peats typically describe the same substance in various stages of decomposition; darker peats are more advanced in decomposition than lighter ones. There are also some differences in the original vegetation that decomposed to make the peat. Besides the peat formed by decomposed sphagnum moss, other peats come from reeds, sedges, and grasses. Reed sedge peat is typically very dark or black and does not have visible peat fibers. It is very difficult to rewet when dried and readily "fixes" phosphate. While the darker grades are more commonly used for amending horticultural soils, some potting blends still use them. Any type of peat will work in mixes, but expect different results with each. Blending of different types of peat is done quite often.

Coir. Coir dust, a mixture of short and powder fibers, is a by-product of the coconut fiber industry. Most coir comes from India, Sri Lanka, the Philippines, Indonesia, and Central America (16). It looks like sphagnum peat but is more granular and does not contain twigs or sticks (17). Coir has a pH of 5.5 to 6.8 and usually contains higher levels of potassium, sodium, and chlorine than peat (18). Coir lasts two to four times longer than peat, but it is more expensive, mainly because of shipping costs (18). Coir is typically shipped in compressed bricks, which expand when wetted. It is easier to wet than peat because there is no waxy cutin to repel water (17). It also has a greater water-holding capacity than peat.

In a study performed in the mid-1990s at Iowa State University, researchers found that petunias and marigolds planted in a mix of 80% coir and 20% perlite grew both taller and heavier (19).
One distributor recommends a mix of three parts coir to one part compost (8). Another offers a product that contains 35 to 45% coir blended with peat moss, vermiculite, and pine bark (18).

There are a few cautions when using coir. Supplemental fertilization with potassium may need to be cut back and nitrogen increased. There is also the possibility of salt damage (20). Salt water is customarily used in the processing of some coir fiber and it is important to purchase only low-salt coir products. It is also wise to ask whether any prohibited wetting agents or binders have been added to any commercial product. Some coir suppliers are listed in Appendix 1.

Newspaper. Ground-up newspapers can be used as a substitute for peat moss in growing media. Newsprint should not be more than 25% by volume of the mix. Avoid the inclusion of glossy paper or paper with colored inks, as these are prohibited.

 

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Ingredients Allowed in Organic Potting Media

Ingredients Allowed in Organic Potting Media

Alfalfa. Alfalfa may be a good locally-available alternative to peat moss. Alfalfa provides nutrients — especially nitrogen — that are released slowly. Raw alfalfa must be processed before use in growing media. Dried alfalfa is ground and passed through a 2-cm screen. Water is added and the alfalfa is allowed to decompose for 20 days. It is then air-dried for another 20 days before use.

Kenaf. Kenaf (Hibiscus cannabinus) is a fibrous plant grown in warmer regions of the U.S. Portions of the plant are used to make paper, and the waste products can be used in growing media. Kenaf stalks contain two different fibers, bast and core. The core material is most suitable as a potting mix ingredient. Growers who have used kenaf have seen excellent results. Two greenhouse studies conducted in 1993 and 1995 showed that coarse-grade kenaf core in a 1:1 ratio with peat moss can be a suitable replacement for bark (21).

Sawdust. The quality of sawdust used as media depends on the wood. Cedar, walnut, and redwood sawdust can be toxic to plants. Oak, hickory, and maple are reputed to tie up soil nitrogen more readily than sawdust from evergreens. Sawdust from treated or painted lumber is not allowed in organic production.

Clay. Several Canadian studies have shown that adding marine glacial clay (a non-swelling mica clay) to sawdust significantly increases the size of greenhouse-grown cucumbers and increases the size and flowering of impatiens and geraniums (22). The researchers tested up to 42.8 grams of clay per liter of sawdust. At North Carolina State, investigators also found that adding arcillite — a calcined montmorillonite and illite clay — to pine bark increased the growth of cotoneaster (23).

Perlite. Perlite is a volcanic rock that is heated and expanded to become a lightweight white material. It is sterile and pH-neutral. When added to a soil mix, perlite can increase air space and improve water drainage. It is a hard material that does not break apart easily. Perlite pieces create tiny air tunnels that allow water and air to flow freely to the roots. Perlite will hold from three to four times its weight in water, yet will not become soggy. It is much lighter than — and can be used instead of — sand.

Vermiculite. Vermiculite is a micaceous mineral that is expanded in a furnace, forming a lightweight aggregate. Handled gently, vermiculite provides plenty of air space in a mix. Handled roughly, vermiculite compacts and loses its ability to hold air. Vermiculite holds water and fertilizer in the potting mix. It also contains calcium and magnesium and has a near-neutral pH. Vermiculite comes in different grades. Medium grade is usually used for starting seeds. A coarse grade can be used in soil mix for older plants.

Limestone. Calcium carbonate (CaCO3) and calcium magnesium carbonate (called dolomitic limestone) are natural forms of lime that are used to adjust pH and provide nutrients. Many other lime products — burned (CaO) and slaked limes (CaOH) — are prohibited. Lime should be well ground for use in growing media.

Alternative Fertilizers. Various organic fertilizers are often used in media. This is especially important in blends that contain little or no compost or soil, since the nutrient content of most other substrates is usually quite low. The base ingredients of the growing media may also influence the choice of fertilizers to be added. Fertilizers that are slowly available may be a poor choice in blends that lack the active microbial complex found in good compost or rich garden soil. Also, many organic fertilizers have a significant effect on pH, and adjustments may need to be made in that regard.

 

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Ingredients Allowed in Organic Potting Media

Ingredients Allowed in Organic Potting Media

Table 1 features a number of the more common organic fertilizers that can be added to growing media. Several characteristics are noted for some of these products, where that information is known.
For more information on these fertilizers and other alternatives, ask for ATTRA's Alternative Soil Amendments [HTML] [PDF/811K]. To locate sources, see the Sources of Organic Fertilizers and Amendments [HTML] resource list.


Table 1. A Selection of Organic Fertilizers for Use in Growing MediaaFertilizer MaterialEstimated N-P-KRate of Nutrient ReleaseSalt and pH Effects



Table 1. A Selection of Organic Fertilizers for Use in Growing Mediaa
Fertilizer MaterialEstimated N-P-KRate of Nutrient ReleaseSalt and pH Effects



Crab Meal10.0 – 0.3 – 0.1Slow
Feather Meal15.0 – 0.0 – 0.0Slow
Fish Meal10.0 – 5.0 – 0.0
Medium
Granite Meal0.0– 0.0 – 4.5Very Slow
Greensand0.0– 1.5 – 5.0Very Slow
Bat Guano5.5 – 8.6 – 1.5Medium
Seabird Guano12.3 – 11.0 – 2.5Medium
Kelp Meal1.0 – 0.5 – 8.0SlowPossibly high-saltDried ManureDepends on sourceMediumPossibly high-saltColloidal Phosphate0.0 – 16.0 – 0.0
Rock Phosphate0.0 – 18.0 – 0.0
Soybean Meal6.5 – 1.5 – 2.4Slow-Medium
Wood Ash0.0 – 1.5 – 5.0FastVery alkaline, saltsWorm Castings1.5 – 2.5 –1.3Medium




(a) Information in the table has been adapted primarily from Penhallegon, Ross. 1992. Organic fertilizer NPK values compiled. In Good Tilth. January. p. 6.; and Rodale Staff. 1973. Organic Fertilizers: Which Ones and How To Use Them. Rodale Press, Emmaus, PA. p. 50.

(b) Cottonseed meal from many sources may be too contaminated by routine pesticide use to be permitted in certified production. Since most cotton is now genetically engineered with Bt genes, it may also be prohibited for this reason. Growers should consult their certifiers before using.

(c) The availability of phosphorus in different forms of rock phosphate depends on the pH of the mix, biological activity, fineness of grind, and the chemical composition of the source rock. Precise performance is not easy to predict.

Mad Cows and Potting Mixes Bovine Spongiform Encephalopathy (BSE), or "Mad Cow Disease," is a fatal brain disorder that can infect humans, where it is recognized as Creutzfeldt-Jakob Disease (CJD) — a devastating illness. According to authorities, BSE is not a problem in the United States (26). However, the fear of BSE and CJD has prompted the Demeter Association — which certifies Biodynamic farms — to completely prohibit the use of bone meal and blood meal, since these could be avenues of infection for BSE (27).
Blood meal, bone meal, and other animal by-products are permitted in certified organic production as soil amendments, though they cannot be fed to organic livestock. As a precaution, dust masks and gloves should be worn when handling these materials.

 

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Recipes for Growing Media

Recipes for Growing Media

These recipes come from a variety of sources and present a wide range of options for working with organically acceptable materials. Because the sources are diverse, units of measurement are also different. When the origin of a recipe is known, or further details and recommendations are known, they have been provided.

The first recipe shown is a classic soil-based formula; the second is a soilless recipe based on the Cornell Mix concept.
Classic soil-based mix

• 1/3 mature compost or leaf mold, screened
• 1/3 garden topsoil
• 1/3 sharp sand

Note: This mix is heavier than modern peat mixes, but still has good drainage. Compost promotes a healthy soil mix that can reduce root diseases. Vermiculite or perlite can be used instead of sand. Organic fertilizer can be added to this base.
Organic substitute for Cornell Mix

• 1/2 cubic yard sphagnum peat
• 1/2 cubic yard vermiculite
• 10 pounds bone meal
• 5 pounds ground limestone
• 5 pounds blood meal

The following four recipes were found in the March–April 1989 issue of the Ozark Organic Growers Association Newsletter. The formulas are credited to the Farm and Garden Project at the University of California, Santa Cruz.
Seedling mix for Styrofoam seedling flats

• 2 parts compost
• 2 parts peat moss
• 1 part vermiculite, pre-wet

Sowing mix

• 5 parts compost
• 4 parts soil
• 1 to 2 parts sand
• 1 to 2 parts leaf mold, if available
• 1 part peat moss, pre-wet and sifted.

Note: All ingredients are sifted through a 1/4-inch screen. For every shovelful of peat, add two tablespoons of lime to offset the acidity.
Prick-out mix for growing seedlings to transplant size

• 6 parts compost
• 3 parts soil
• 1 to 2 parts sand
• 1 to 2 parts aged manure
• 1 part peat moss, pre-wet and sifted
• 1 to 2 parts leaf mold, if available
• 1 6-inch pot bone meal

Special potting mix

• 1 wheelbarrow-load sifted soil
• 1 wheelbarrow-load aged manure
• 1 wheelbarrow-load sifted old flat mix
• 5 shovelfuls sifted peat
• 2 4-inch pots bone meal
• 2 4-inch pots trace mineral powder
• 2 4-inch pots blood meal

The following recipes are taken from John Jeavons's How to Grow More Vegetables…, Ten Speed Press, Berkeley, CA.
Classic planting mix
One part each by weight:

• compost (sifted, if possible)
• sharp sand
• turf loam (made by composting sections of turf grass grown in good soil)

Note: the mixture should be placed in growing flats on top of a 1/8-inch layer of oak leaf mold to provide drainage. Crushed eggshells should be placed between the leaf mold and compost for calcium-loving plants like cabbages and carnations.
Simple soil flat mix
Equal parts by volume:

• compost
• bed soil (saved from a biointensive production bed during double-digging process)

The next three formulas are credited to the 1992 NOFA-NY Organic Farm Certification Standards.
Classic formula for horticultural potting mix

• 1/3 mature compost or leaf mold, sieved
• 1/3 fine garden loam
• 1/3 coarse sand (builder's sand)

Sterile peat-lite mix

• 1/2 cubic yards shredded sphagnum peat moss
• 1/2 cubic yards horticultural vermiculite
• 5 pounds dried blood (12% N)
• 10 pounds steamed bone meal
• 5 pounds ground limestone

Recipe for soil blocks

• 20 quarts black peat with 1/2 cup lime
• 20 quarts sand or calcined clay
• 20 quarts regular peat with 1 cup of greensand, 1 cup of colloidal phosphate, and 1 cup blood meal
• 10 quarts soil
• 10 quarts compost

Note: all bulk ingredients should be sifted through a 1/2-inch screen.

 

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Recipes for Growing Media

Recipes for Growing Media

The following four recipes are credited to Eliot Coleman. The first was published in the Winter 1994 issue of NOFA-NJ Organic News, in an article by Emily Brown-Rosen. The remaining three are adapted from Coleman's book The New Organic Grower (see Appendix 2).
Organic potting mix

• 1 part sphagnum peat
• 1 part peat humus (short fiber)
• 1 part compost
• 1 part sharp sand (builder's)

To every 80 quarts of this add:

• 1 cup greensand
• 1 cup colloidal phosphate
• 1 1/2 to 2 cups crab meal, or blood meal
• 1/2 cup lime

Blocking mix recipe

• 3 buckets (standard 10-quart bucket) brown peat
• 1/2 cup lime (mix well)
• 2 buckets coarse sand or perlite
• 3 cups base fertilizer (blood meal, colloidal phosphate, and greensand mixed together in equal parts)
• 1 bucket soil
• 2 buckets compost

Mix all ingredients together thoroughly. Coleman does not sterilize potting soils; he believes that damp-off and similar seedling problems are the result of overwatering, lack of air movement, not enough sun, over-fertilization, and other cultural mistakes.
Blocking mix recipe for larger quantities

• 30 units brown peat
• 1/8 unit lime
• 20 units coarse sand or perlite
• 3/4 unit base fertilizer (blood meal, colloidal phosphate, and greensand mixed together in equal parts)
• 10 units soil
• 20 units compost

Mini-block recipe

• 16 parts brown peat
• 1/4 part colloidal phosphate
• 1/4 part greensand
• 4 parts compost (well decomposed)

Note: If greensand is unavailable, leave it out. Do not substitute a dried seaweed product in this mix.
The next recipe and details come from John Greenier, of Stoughton, Wisconsin. They were published in the January 1996 issue of Growing for Market.
Seedling mix for soil blocks or seedling flats

• 2 3-gallon. buckets sphagnum peat moss
• 1/4 cup lime
• 1 1/2 cups fertility mix
• 2 cups colloidal (rock) phosphate
• 2 cups greensand
• 2 cups blood meal
• 1/2 cup bone meal
• 1/4 cup kelp meal
• 1 1/2 buckets vermiculite
• 1 1/2 buckets compost

Directions for mixing:

1. Add peat to cement mixer or mixing barrel.
2. Spread the lime and fertility mix over the peat.
3. Mix these ingredients thoroughly.
4. Add the compost and vermiculite and mix well again. When done, examine the distribution of vermiculite to ensure that it has been mixed in evenly.

Note that all bulk ingredients should be screened through 1/4-inch hardware cloth. Well matured, manure-based compost should be used (avoid poultry manure and wood-chip bedding).
The next two recipes were published in the September 1990 issue of Greenhouse Manager in an article entitled "Recipes for Success in Media Mixes," by Kathy Z. Peppler.
Growing mix for packs

• 40% topsoil
• 40% Canadian-type Michigan peat
• 20% perlite
• 5 pounds lime per cubic yard
• 3 pounds dolomitic lime per cubic yard

Note: The topsoil and peat are sterilized early in the fall, then brought indoors to be blended with the other ingredients and stored inside.
Growing mixes for pots and baskets

• 30% topsoil
• 60% peat
• 10% perlite
• 5 pounds lime per cubic yard
• 3 pounds dolomitic lime per cubic yard

Note: The handling of this pot mix is the same as for pack mix.
The following recipes and instructions are from a workshop entitled "Getting Started in Organic Market Gardening," which was offered as part of the March 2001 "Organic University" program sponsored by Midwest Organic and Sustainable Education Services (MOSES) in conjunction with its Upper Midwest Organic Conference. The first is credited to Tricia Bross Luna Circle Farm, Gays Mills, WI; the second is credited to Steve Pincus, Tipi Produce, Madison, WI.
Luna Circle recipe

• 2 buckets black peat (1 bucket = 8 quarts)
• 1/2 bucket compost
• Fertility mixture:
  • 1 cup greensand
  • 1 cup rock phosphate
  • 1 cup kelp meal
  • 2 buckets sphagnum peat moss
  • 1 bucket sand
  • 1 bucket vermiculite

Directions for mixing:

• Screen the peat and the compost and combine with the fertility mix.
• Mix well.
• Add the sphagnum, sand, and vermiculite.
• Mix well again.

Tipi Produce recipe

• 2 bales sphagnum peat moss (3.8 or 4.0 cubic foot bales)
• 1 bag coarse vermiculite (4.0 cubic foot bags)
• 1 bag coarse perlite (4.0 cubic foot bags)
• 6 quarts of a fertilizing mixture comprised of:
  • 15 parts steamed bone meal
  • 10 parts kelp meal
  • 10 parts blood meal
  • 5 to 10 parts dolomitic limestone (80 to 90 mesh)

Note: This mix works well in small and medium plug trays and 1020 flats for growing lettuce, onions, leeks, peppers, tomatoes, melons, squash, cucumbers, and many flowers. When repotting small plugs into larger cells, add about 1/3 by volume of old leaf mold or compost and more fertilizing mixture. Continue to fertilize twice per week with soluble fish and seaweed fertilizer.
The following three recipes are adapted from a subchapter entitled "Using compost for container crops and potting mixes" in On-Farm Composting Handbook, by Robert Rynk, (ed.). 1992. PublicationNRAES-54. Northeast Regional AgriculturalEngineering Service, Cornell Cooperative Extension,Ithaca, NY. 186 p.
Vegetable transplant recipe
Equal parts by volume of:

• compost
• peat moss
• perlite or vermiculite

Bedding plant recipe

• 25% compost
• 50% peat moss
• 25% perlite or vermiculite

Container mix for herbaceous and woody ornamentals
Equal parts by volume of:

• compost
• coarse sand
• peat moss or milled pine bark

The following two simple recipes came from Mark Feedman, a practitioner of the Biodynamic-French Intensive system. The first mix was used with great success while doing development work in the Dominican Republic; the second is an adaptation used later in New Mexico.
Dominican Republic mix
Equal parts:

• fine loam soil
• sharp horticultural sand
• well-finished leaf mold

New Mexico mix

• 2 parts well-finished compost
• 2 parts good topsoil
• 1 part leaf mold

 

[Coba]

Recipes for Growing Media

Recipes for Growing Media

The remaining recipes in this appendix are of uncertain origin, but were published in earlier versions of ATTRA's Organic Potting Mixes.
Recipe #1

• 50 to 75% sphagnum peat moss
• 25 to 50% vermiculite
• 5 pounds ground limestone per cubic yard of mix

Recipe #2

• 6 gallons sphagnum peat moss
• 1/4 cup lime
• 4 1/2 gallons vermiculite
• 4 1/2 gallons compost
• 1 1/2 cups fertility mix made of:
• 2 cups colloidal (rock) phosphate
• 2 cups greensand
• 1/2 cup bone meal
• 1/4 cup kelp meal

Recipe #3

• 10 gallons sifted two-year-old leaf mold
• 10 gallons sifted compost
• 5 to 10 gallons sphagnum peat moss
• 5 gallons perlite
• 5 gallons coarse river sand
• 2 cups blood meal
• 6 cups bone meal

Recipe #4

• 40 quarts sphagnum peat moss
• 20 quarts sharp sand
• 10 quarts topsoil
• 10 quarts mature compost
• 4 ounces ground limestone
• 8 ounces blood meal (contains 10% nitrogen)
• 8 ounces rock phosphate (contains 3% phosphorus)
• 8 ounces wood ashes (contains 10% potassium)

Recipe #5

• 9 quarts compost
• 1 cup greensand
• 3 quarts garden soil
• 1/2 cup blood meal
• 3 quarts sharp sand
• 1/2 cup bone meal
• 3 quarts vermiculite

Recipe #6

• 1 part peat
• 1 part bone meal
• 1 part perlite
• 1 part compost (or leaf mold)
• 1 part worm castings (optional)

Recipe #7

• 2 parts vermiculite
• 3 parts peat
• 2 parts perlite
• 2 parts cow manure
• 3 parts topsoil
• 1/2 part bone meal

Recipe #8

• 15 quarts screened black peat
• 15 quarts brown peat
• 17 quarts coarse sand
• 14 quarts screened leaf compost
• 3 ounces pulverized limestone
• 9 ounces greensand
• 3/4 cup dried blood
• 3 ounces alfalfa meal
• 3 ounces colloidal phosphate
• 9 ounces pulverized bone meal

Recipe #9

• 10 pounds compost
• 30 pounds sphagnum peat moss
• 60 pounds white sand
• 8 pounds calcium carbonate
• 4 pounds soft rock phosphate
• 2 pounds sawdust

Recipe #10

• 70 pounds white sand
• 25 pounds sphagnum peat moss
• 5 pounds chicken manure
• 8 pounds calcium carbonate
• 4 pounds soft rock phosphate

 

[Coba]

Cation Exchange Capacity (CEC)

Cation Exchange Capacity (CEC)

Cations are positively charged ions such as calcium (Ca2+), magnesium (Mg2+), and potassium (K+), sodium (Na+) hydrogen (H+), aluminum (Al3+), iron (Fe2+), manganese (Mn2+), zinc (Zn2+) and copper (Cu2+).

The capacity of the soil to hold on to these cations called the cation exchange capacity (CEC). These cations are held by the negatively charged clay and organic matter particles in the soil through electrostatic forces (negative soil particles attract the positive cations). The cations on the CEC of the soil particles are easily exchangeable with other cations and as a result, they are plant available. Thus, the CEC of a soil represents the total amount of exchangeable cations that the soil can adsorb.

CEC is highly dependent upon soil texture and organic matter content. In general, the more clay and organic matter in the soil, the higher the CEC. Clay content is important because these small particles have a high ration of surface area to volume. Different types of clays also vary in CEC. Smectites have the highest CEC (80-100 millequivalents 100 g-1), followed by illites (15-40 meq 100 g-1) and kaolinites (3-15 meq 100 g-1).

Examples of CEC values for different soil textures are as follows:

Soil texture CEC (meq/100g soi)Sands (light-colored)3-5Sands (dark-colored)10-20Loams10-15Silt loams15-25Clay and clay loams20-50Organic soils50-100



In general, the CEC of most soils increases with an increase in soil pH.


Two factors determine the relative proportions of the different cations adsorbed by clays. First, cations are not held equally tight by the soil colloids. When the cations are present in equivalent amounts, the order of strength of adsorption is Al3+ > Ca2+ > Mg2+ > K+ = NH4+ > Na+.

Second, the relative concentrations of the cations in soil solution helps determine the degree of adsorption. Very acid soils will have high concentrations of H+ and Al3+. In neutral to moderately alkaline soils, Ca2+ and Mg2+ dominate. Poorly drained arid soils may adsorb Na in very high quantities.

http://soils.tfrec.wsu.edu/webnutritiongood/soilprops/04CEC.htm
http://nmsp.cals.cornell.edu/publications/factsheets/factsheet22.pdf

 

[Coba]

Cation Exchange Capacity (CEC)

Cation Exchange Capacity (CEC)

Organic matter can have a 4 to 50 times higher CEC per given weight than clay. The source of negative charge in organic matter is different from that of clay minerals; the dissociation (separation into smaller units) of organic acids causes a net negative charge in soil organic matter, and again this negative charge is balanced by cations in the soil.

Because organic acid dissociation depends on the soil pH, the CEC associated with soil organic matter is called pH-dependent CEC. This means that the actual CEC of the soil will depend on the pH of the soil. Given the same amount and type of organic matter, a neutral soil (pH ~7) will have a higher CEC than a soil with e.g. pH 5, or in other words, the CEC of a soil with pH-dependent charge will increase with an increase in pH.

Base Saturation

The proportion of CEC satisfied by basic cations (Ca, Mg, K, and Na) is termed percentage base saturation (BS%). This property is inversely related to soil acidity. As the BS% increases, the pH increases. High base saturation is preferred but not essential for tree fruit production. The availability of nutrient cations such as Ca, Mg, and K to plants increases with increasing BS%. Base saturation is usually close to 100% in arid region soils. Base saturation below 100% indicates that part of the CEC is occupied by hydrogen and/or aluminum ions. Base saturation above 100% indicates that soluble salts or lime may be present, or that there is a procedural problem with the analysis.

​

CEC and Availability of Nutrients
Exchangeable cations, as mentioned above, may become available to plants. Plant roots also possess cation exchange capacity. Hydrogen ions from the root hairs and microorganisms may replace nutrient cations from the exchange complex on soil colloids. The nutrient cations are then released into the soil solution where they can be taken up by the adsorptive surfaces of roots and soil organisms. They may however, be lost from the system by drainage water.

Additionally, high levels of one nutrient may influence uptake of another (antagonistic relationship). For example, K uptake by plants is limited by high levels of Ca in some soils. High levels of K can in turn, limit Mg uptake even if Mg levels in soil are high.

Anion Exchange
In contrast to CEC, AEC is the degree to which a soil can adsorb and exchange anions. AEC increases as soil pH decreases. The pH of most productive soils in the US and Canada is usually too high (exceptions are for volcanic soils) for full development of AEC and thus it generally plays a minor role in supplying plants with anions.

Because the AEC of most agricultural soils is small compared to their CEC, mineral anions such as nitrate (NO3- and Cl-) are repelled by the negative charge on soil colloids. These ions remain mobile in the soil solution and thus are susceptible to leaching.

​

 

[TrichyTrichy]

Wow!!!

 

[RanchoDeluxe]

Nice thread Coba. Gonna have to sit down and read the entire thing soon. Be ready for some questions.

Nice work man.

 

[Coba]

I should add... post #4 through #11 are copyrighted from ATTRA by;
George Kuepper
NCAT Agriculture Specialist
and Kevin Everett, Program Intern
© NCAT September 2004
Reviewed October 2010
IP112

I don't mean to plagiarize. just inform.

I feel Topsoil is a vital part of organic living soil. like VerdantGreen and Gascanastan, i feel we need more emphasis on topsoil in our living soil recipes.

Thanks RD and TT!

 

[EclipseFour20]

A couple of documents that: confirmed my suspicions as well as proved me wrong--AND directed me to some interesting ideas/concepts of old ways--

From Rutgers--
Fundamentals of Container Media Management, Part 1: Physical Properties--
"The successful production and management
of high quality container-grown plants requires
an understanding of the unique environment
found in containers and how it is affected by the
physical and chemical properties of the growing
media."

http://njaes.rutgers.edu/pubs/publication.asp?pid=FS812

...and Part 2, Measuring Physical Properties--
"The physical properties of a growing medium
should be known before a crop is established. In cases
of problems due to inadequate physical properties, like
poor aeration or reduced water holding capacity, the
presence of a plant does not allow for adjustments of the
medium’s physical composition. It is therefore extremely
important to know the physical characteristics
of the medium beforehand to allow for appropriate
adjustments before planting the crop. Unfortunately, it
is common to find out that neither the physical nor the
chemical characteristics of media are evaluated routinely
by growers. Such analyses are most likely
conducted only after problems arise with the crop, and
very often too late to be resolved."

http://njaes.rutgers.edu/pubs/publication.asp?pid=FS881

From NCSU--
Greenhouse Substrates and Fertilization--
"Everyone seems to be searching for the ideal
plant mix. The criteria are simple: make a mix
with good aeration, that doesn’t dry out too quickly,
can be used in all cell sizes, contains all the nutrients necessary,
can be used for all species of and stores indefinitely. All
that is needed is a substrate that is not affected by other
forces in the greenhouse; a mix that does not change
with cultural practices."

http://www.ces.ncsu.edu/depts/hort/floriculture/plugs/ghsubfert.pdf

...and from FAO (don't laff)...a mini textbook on substrates--

http://www.fao.org/hortivar/scis/doc/publ/8.pdf

Soil porosity is one key for a "happy soil"!

Cheers!

 

[Coba]

Soil porosity is one key for a "happy soil"!

Cheers!

"[FONT=Arial, Helvetica, sans-serif]In general, soil consists of approximately 45% mineral material, 5% (or less) organic matter and 50% pore space (which is occupied by air and/or water)."
[/FONT][FONT=Arial, Helvetica, sans-serif]
[/FONT]

 

[EclipseFour20]

Coba...lots of rules of thumbs out there...the Rutgers "part II" article explains how to measure the soil medium characteristics: bulk volume, air porosity, water holding capacity, and plant available water. There really is more than 50/50 or 45/5/50 mix ratio.

Do the experiments then...adjust ratios, and repeat; when I did--I obtained really interesting and surprising results. After making the adjustments to my custom soil mix...and started pre-moistening the medium 24 hours prior to transplant (tip from the NCSU article)...I am more than happy with the results--and more than happy with the efficiency (soil requires about 25% less ferts...while providing me with nice bump in harvest...10-15%--depends on the strain).

 

[Neo 420]

Awesome information!! Would have like to have seen some fishbone/fish meal additions but great work!