Five Important Substrate Properties

Five Important Substrate Properties

There are really only 5 important substrate properties. total pore space, water holding capacity, air space, bulk density and particle size distribution Without these proper physical properties nutrients in the compost will not be effective. We all know a good substrate must drain well but not get too dry nor retain too much water. It should be always moist yet not hold too much water. The ideal potting mix should be able to be watered every day so as to bring water, nutrients and air to the plant roots. The water applied every day from the top of the pot drives old air containing carbon dioxide out from the bottom and suck fresh air in from the top. It can do all this via the above stated physical properties. I grew up in Florida. These were my formative years. Somehow I grew an affinity for plants, flowers in particular during this time. So when I came across this very well put together .pdf file from the University of Florida, it caught my eye. Check it out. It is all about substrate particle size properties....

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pH and Organic Substrate Nutrients

pH and Organic Substrate Nutrients

Nearly all of us are familiar with pH as a method to quantify fluids to ascertain if they are acidic or basic. It is common knowledge the scale goes from 1 to 14 with 1 to 6 being acidic, 7 neutral and 8 to 14 basic. The pH shows the concentration of hydrogen ions, H+, within the liquid. So why is the topic of pH so basic whenever we discus live organic soils? The reason is that pH impacts what kinds of microbes live in the soil. Different microbes promote or suppress nitrification along with other organic behavior which impact the way plants develop and grow. Bacteria will increase the pH while fungus lowers it. The soil pH is effected by microbes more than the microbe is affected by the soil. . Preferred pH levels of Different Plants As we all know, every plant has it’s preference for a certain pH level. But ideal pH for any plant, has more to do with its preference for a specific bacteria and/or fungus  than it does with the biochemistry of pH. This is not to say certain nutrient up-takes are not effected by pH. Refer to the chart on the right.(click to enlarge) It outlines which elements are available at what pH. This is standard biochemistry. So there are two points to consider here… plant microbe preference and elemental behavior at specific pH levels. In general, woody forest plants such as trees and bushes have fungal symbiosis. Fungus thrives in low, acidic pH. So you will find acidic soils in the forests. In contrast, soft vegetative plants, such as our precious herbs, have a symbiotic relationship with bacterias. Bacterias thrive in their low, basic pH environ. So would you say herbs prefer a low pH or would it be more descriptive to say veggies grow better in a highly bacterial soil? . Hydrogen is a Cation The hydrogen cation is used as an exchange currency for other cations in the exchange. When you have a great deal of hydrogen ions, the pH is minimal and the liquid is said to be acidic. In a similar fashion, when you have few hydrogen ions in the liquid, it is said to have a high pH, which is alkaline or basic. I have always wondered why a pH is LOW when it has HIGH amounts of Hydrogen. This is because when calculating the pH mathematically, a negative logarithm is used. (see formula below) We are herb growers and therefore really don’t need to be experts and learn that much more about pH. However we do need to know that each time an herb plant’s root tip interchanges a H+ cation for a nutrient cation, the amount of hydrogen ions within the liquid will increase. Because the concentration of H+ cations increases, the pH decreases, which makes the substrate progressively more acidic as nutrient up-take increases. But the pH many times,  balances out since roots (click on image right) also take up negatively charged anions. Just as plant roots use H+ as an exchange currency for cation exchanges, they use hydroxy, OH- for an anion exchange currency. More OH-, in your solution increases the pH since it reduces the percentage of H+ cations. Amazingly, fungi and bacteria are little enough to receive and shed cations and anions on their surface area, electrolytically retaining or expelling mineral nutrients from decomposition in the soil. This, also, has an influence on the pH. So with so many variables effecting the balance, being aware of the substrate’s pH is helpful in choosing what you need to add to the...

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Chelation and Live Organic Soils

Chelation and Live Organic Soils

The word chelate translated from the Greek word “chel”, means crab’s claw. It refers to the claw like manner in which a metal (usually iron) is loosely bound in a chelated molecule. Elements are more easily absorbed by plant roots in chelated form than elements that are not chelated. Chelates are organic molecules that can retain or release specific metal ions. These ions would include plant nutrients such as calcium, magnesium, cobalt, copper, zinc, iron and manganese. A chelate is a molecular compound forming a complex of cations with organic compounds forming a ring structure. Upon entering plant cells cationic nutrients will form chelates with organic and amino acids. Chelation enables the nutrients to move freely inside the plants. The chelation process increases the mobility and therefor availability of nutrients to plants. . Chelates And Cation Exchange Capacity Chelate’s end effect is much like a cation exchange in the sence that they hold elements until they are needed and then releases them for plant use, but the chemistry for doing this is different. Chelates work outside and inside of the plant. Outside the plant cell, in the soil, a chelated element is kept in reserve and can not form a compound with another element and participate out of the water medium. Once inside a plant cell some metals are prohibited from moving freely. But when they are in chelated form the needed metal is able to move readily inside the cell and from cell to cell. Chelation, Chlorophyll and Blood Chelation takes place not just in the soils and plants. It is an ongoing fundamental process in plants and animals. Us humans are dependent on the continual process of chelation as well… in our blood for example. You and I are more related to our herb plants than we think. Both of us rely on a chelating compound, fundamental to our structure. Within humans, it’s the deeply crimson heme which transports, via our blood, the much needed oxygen cycled by vegetation. Plants as well have a vital chelation substance, green chlorophyll. It is so related to heme that you only have to exchange an iron atom for a magnesium atom, to have the identical molecular structure. Examples of Chelated Elements Chelates are constructed from the complexing of cations with organic compounds resulting in a ring structure. If you click on the examples below you can see the central M (metal) in the chelate “claw”. The metal will will not participate out of solution and once inside the cell, will be released when needed. . Positive Aspects of the Chelation Process: 1. Increase in available nutrients. Chelating agents will bind insoluble iron in alkaline soils and substrates to make them available to plants. 2. Prevents nutrients from forming insoluble, unavailable compounds. Chelating agents of metal ions will protect the chelated ions from unwanted chemical reactions and therefor increase the availability of those ions for plant uptake. 3. Chelates reduce toxicity of some metal ions to plants. Chelation in substrates reduces the concentration of metal ions to a normal beneficial level. The process is done via humic acid and high molecular weight compounds found in organic matter. 4. Chelates prevent nutrients from wash out. Metal ions which form chelates are much more stable than free ions. 5. The chelation process increases the mobility and therefor availability of nutrients to plants. 6. Chelating agents reduces the growth of plant pathogens by reducing available iron....

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Colloids in Substrates | Clays vs Humus

Colloids in Substrates | Clays vs Humus

Soil colloids are the most dynamic part of all soils and substrates. It establishes their chemical and physical attributes. Two of the most important colloids in soils are clay and humus. However,  substrates for potting mixes humus  is king. So Heads Up! This is very important. In typical soil it is the inorganic colloids, mostly clays, that are the most abundant components. However, in a well made substrates for potting mixes it is the tiny organic humus, less than 0.001 mm across that will determine the availability of nutrients for the plant. Organic humus colloids are many times more active than inorganic clays because of their higher CEC. It is fairly easy to add enough humus in potting soil where as field soils are too extensive. For a good potting soil, what needs to be done is pack the substrate with the optimal quantity of humus. Younger plants need less nutrition. Too many colloids charged with nutrients will burn it. . Characteristics of a Colloid Humus is amorphous, meaning their physical and chemical characteristics are not very well defined. Clay particles are normally crystalline, making clay’s physical and chemical characteristics anamorphic. Both inorganic and organic colloids are  components of most soils and substrates. (When I speak of “soil” I am referring to soils in fields. When I us the term “substrate”, I am referring to potting mixes.) The majority of the substrate solids like coco fiber and peat moss, are inert leaving the organic humus to define the substrate’s physical and chemical properties. So, when looking for a well made, effective substrate, look toward the quantity and quality of the humus ingredients. The passive biochar humus and the active humus in the compost are chief concerns. Since organic humus does the same job as clay but better, don’t look for clay in a substrate. .   The most essential quality of a colloids is its capacity to adsorb, keep for a time, then discharge ions on its surface. Most colloids have an overall negative charge due to their chemical and physical make up. That negative charge will be balanced out through a large number of cations attracted to its outer surface. Therefore, colloids could be seen as large anions covered with a group of rather loosely stored cations. Typical water molecules can also be adsorbed onto colloid surfaces. They will be found in the hydrated arrangement on the cations. The volume of water around a specific cation is very important, since the effective radius of the cation goes up with more H2O or down with less. . The Size of Colloids Colloid’s characteristic of being very small, is important to the cation exchange. For example, take a clay particle, known for its high cation exchange capacity. The individual clay particles are so tiny, you can not distinguish one from the other under a microscope. These small particles, when mixed in water, do not dissolve but are suspended indefinitely. They do not settle as sediment at the bottom of the container nor are in solution. A substance with this suspension characteristic is called a colloid. As mentioned, the size of the particle is very important. If a substance is small enough, when there is a positive or negative charge close to them they are effected… attracted or repulsed. This would not happen to a larger particle because if its greater mass. All small partials are effected by electrostatic charges, even bacteria and fungus. Humus is a colloid, which, like all colloids, does not float to the top nor settle out to the bottom. Colloids because of their miniscule size have...

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Cation Exchange Capacity of Humus

Cation Exchange Capacity of Humus

The cation exchange capacity (CEC) of the soil is merely a way of measuring the amount of sites in soils or soil humus that have a negative charge. These hold on to positively charged particles (cations) by means of its electrostatic properties. The amount of such exchange sites measures the capacity in the soil to keep nutrients, or the cation exchange capacity (CEC). So a soil’s CEC is the sum of negatively charged nutrient exchange sites  per unit weight or volume. CEC is calculated in milligram equivalents per 100 grams (meq/100g). Adding the concentrations of each cation gives a figure of the overall  CEC. A figure above 10 (meq/100g) is preferred for normal plant growth . However substrates with high levels of humus can have a CEC of 30 (meq/100g) or more. The 5 most important cations in soils are calcium (Ca++ ), magnesium (Mg++), potassium (K+), sodium (Na+) and aluminium (Al+++). . Cations and Anions What we really need to understand is that the greater the CEC value, the more nourishment a substrate or soil can have ready for use. The higher the CEC value, the more effective it can be for improving plant growth, vigor and health. All very small particles, not just humus and clay, carry electrical charges. The part of the nutrient that carries the electrical charge are called ions. Ions with a positive charge are called cations and ions carrying a negatively charged are called anions. . Humus and Available Nutrients Depending on the soil or substrate, there are a few ingredients that have cation exchange capacity. The element having the highest CEC would be humus. Organic substrates all contain a good amount of this organic compound. Cations held by the electrostatic force of the soil’s humus can be easily exchanged for other cations within the soil making them readily available for plant uptake in the rhizosphere. Therefore, the CEC is crucial for knowing if there are sufficient amounts of AVAILABLE nutrients in the soil that have a positive charge. . Common Nutrient Cations And Anions Some important positively charged nutrients include,  Ca++, Mg++ and K+. You may note that a very important nutrient, Nitrate NO3-, is not listed. This is because it carries a negative charge. Humus has not only negatively charged ions ready for retaining positively charged minerals, some have positively charged ions as well which can hold on to negatively charged minerals such as our precious nitrates and nitrites. However the anion exchange is very low in relation to cation exchange sites and unfortunately doesn’t come into account when talking nitrate availability. Examples of Cations: NH4+, Ca++, Mg++, K+ Examples of Anions: NO3-,  Cl-, SO4-, PO4- . How Plants Eat The surface areas of a plant root hairs contain their own electrical charges. Any time a plant’s root hair penetrates the substrate, it may exchange its own cations for those mounted on humus or clay debris and then absorb the cation nutrient for intake as nourishment. Plant roots use a hydrogen cation (H+) for the exchange. They eject one hydrogen cation for every cation nutrient adsorbed. This keeps a charge balance. This is the way plant life eats. This is a basic function of all plant life. . If there is a larger concentration of one specific cation over the others in the soil water, that cation will force the other cations off the colloid and the abundant cation element take their place. . Absorbsion vs Adsorbsion Positively charged particles are electrostatically attracted to negatively charged particles. We all know this intuitively from our times spent playing with magnets as a...

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Humus | What It Is

Humus | What It Is

All organic matter, as it decomposes, forms smaller and smaller particles. When it breaks down as far as it can and yet still can be identified as organic matter, it is called humus. The process of “humification” takes place naturally in soil and substrates, or in the production of special compost, like the bakashi. While plants die-off and are broken down into simpler compounds by microbial fungi and bacteria they’re eventually transformed into humus. All humus is a carbon based, organic substance. It is made of extended, tough chains of carbon compounds with a sizable surface area. The surface areas hold electrical charges, that draw in and store nutrient particles called cations. Humates are notable for their humic acids, namely Humic, Fulvic, and Ulmic. Humus is known as a colloidal substance, and boosts the soil or substrates cation exchange capacity, CEC. Humus is the “life-force” of living organic potting soil. Humus | Decomposing Matter The difference between humus and compost is that decomposing compost matter is an inhomogeneous substance, with rough plant parts observable. An entirely humified organic substance, on the other hand, will be consistent in character, with specific shape and structure. Humus is the ultimate stage in the decomposition of organic matter. Humified organic matter, observed through an electron microscope, will show very small yet plainly recognizable plant remnants which can only be mechanically broken down once the decomposition has been completed. The image on the right is an electron microscope rendition of humus/brown, decaying compost/green, and mineral particles/purple.  Scientist and researchers have a very specific definition of humus but not so in our horticultural community. . Active and Passive Humus Rich compost, ready to apply is generally known as active humus. It is applied as a top dressing or as a substrate component with organic compounds that will release more nutrients when they are decomposed further. But in scientific circles, if the organic compound is not totally decomposed, it is not humus at all. Researchers define humus as a stable, passive molecule  which would not change structures in the soil unless it is a simple mechanical breakage into two or more pieces. But for horticulturalist, humus comes in active and passive forms. Active humus in compost is still abundant in plant remains unbroken into it’s simpler stable form. Passive humus composed of humic acids and humins, will be so very insoluble they can’t be divided further by microorganisms. Therefore passive humus is considerably immune to additional decomposition and provides very few readily accessible nutrition to soils and/or substrates themselves. . Benefits of Humus There are many benefits to plants which humus provides. Humus can hold up to 90% of its mass in water, and so enhances the soil’s ability to store water. The chemical composition of humus allows it to buffer abnormally high or low levels of pH in the soil. Harmful elements including heavy metals and even too much nutrients, will be chelated, which means bound to the organic compounds of humus and kept from moving into the system. Also, during the humification, fungi and bacteria always exude sticky gums that promote a beneficial assembly of the potting soil by maintaining particles together. This allows even better oxygenation of the soil substrate. Particle distribution size is a very important physical determinant to soil drainage and oxygen supply. Larger particles allow for more air and less saturation of water. The biggest benefit of humus however is its colloidal characteristics. Humus is THE number one ingredient that will maintain nutrients (cations) in substrates so they will not wash away when watered. At the same time the collation...

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