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Soil Doctors

By Soil Doctors 28 Nov, 2017

Water is the driving force of all nature.

“Hydrophobicity” ( Hydro  meaning “water”  phobic  meaning “fear”), is the physical property of a molecule that is repelled from water - a molecule known as a Hydrophobe . A classic example of a hydrophobe is oil - it will not mix with water. Hydrophobic soils contain hydrophobes and resist moisture penetration. Hydrophobes are organic molecules and are very common in our environment.
They are found in soils as the result of naturally decomposed plant tissues, microbial by-products, naturally occurring waxes and resins, and organic matter such as those found in mulches and potting mixes.

Hydrophobicity develops in soils when hydrophobes surround the soil particle forming a waxy coating, or intermix with minerals currently in the soil. Moisture migration through hydrophobic soil is irregular and non-uniform. The soil does not wet and water runs off or moves through fissures and cracks.

Water is the key to life on earth. Liquid H2O is at the heart of all ecosystems and access to water can determine the survival of an organism. Ensuring water reaches the roots of plants is essential and the primary process from which all others follow.

Movement of water is affected by three forces;

1. GRAVITY  - Constant downward pull

2. COHESION  - The attraction of water molecules to each other   (the force that holds a water droplet together)

3. ADHESION  - The force attracting water molecules to other   substances. (i.e. soil)

In hydrophobic soil, the hydrophobes disrupt adhesion and the cohesive force is stronger. Water molecules 'bead' together, resisting the soil and running off with the force of gravity - down gradients or through cracks. When soil is hydrophobic, action is required reduce the cohesive forces and allow water to 'stick' to the soil again .

Even minimal levels of water repellency can negatively impact water movement in soils, resulting in preferential flow/channeling patterns that encourage nutrient leaching and non-uniform distribution of applied water and input chemicals. This reduced effectiveness of water movement and poor distribution of fertilizer and chemical inputs can result in reductions in plant growth and vigour, as well as crop yield and quality.

By Soil Doctors 27 Nov, 2017

Plants take up the majority of their nutrient needs from the soil by utilizing different transport mechanisms. Different characteristics of soils affect their nutrient-holding capacity and which mechanisms work best. Some macronutrients, particularly nitrogen and phosphorus, cycle between residency in the soil, usage by plants, and air- and water-borne particles. These have important environmental effects, and the actions of these cycles influences management.

The soil solution is the liquid in the soil. Plant nutrients (solids and gases) dissolved in the soil solution can move into the plant as the water is taken up by the roots. This is the medium through which most nutrients are taken up by the plant. Cations are positively-charged ions (such as Ca2+, Mg2+, K+, and NH4+) which are held on anionic (negatively-charged) exchange sites in the soil. Cation Exchange Capacity (CEC) is a measure of the amount of cations that can be held by the soil and released into the soil solution. Soils with a greater cation exchange capacity are able to hold onto more nutrients. Soil organic matter refers to hydrocarbon compounds in various stages of decomposition. Humus is organic material resistant to further decomposition, and which does not supply many nutrients. It can cause a negative charge in the soil, increasing CEC.

Mineralization is the conversion of a nutrient from the organic (i.e. bound to carbon and hydrogen) form to the inorganic form. The process occurs when organic materials, such as soil organic matter, manure, plant residue, or biosolids, are decomposed by soil microorganisms. The nutrient is released, and is available for uptake by new plants. Immobilization is the reverse process of mineralization, wherein nutrients are converted from the inorganic to organic forms (i.e. taken by soil microbes and incorporated into their cells), making them unavailable to plants. Nutrient uptake antagonism refers to the competition between nutrients for uptake by plants. The two nutrients, often ions with the same charge, are said to be antagonistic with regard to the other. Some examples include


  • Phosphorus Excess Can Lead To Reduced Zinc Uptake
  • Calcium Excess Can Cause Boron Or Magnesium Deficiencies
  • Potassium Excess Has Been Found To Reduce Magnesium Uptake And Vice Versa

Mass flow is the movement of dissolved nutrients into a plant as the plant absorbs water for transpiration. The process is responsible for most transport of nitrate, sulfate, calcium and magnesium. Diffusion is the movement of nutrients to the root surface in response to a concentration gradient. When nutrients are found in higher concentrations in one area than another, there is a net movement to the low-concentration area so that equilibrium is reached. Thus, a high concentration in the soil solution and a low concentration at the root cause the nutrients to move to the root surface, where they can be taken up. This is important for the transport of phosphorus and potassium. Root interception occurs when growth of a root causes contact with soil colloids which contain nutrients. The root then absorbs the nutrients. It is an important mode of transport for calcium and magnesium, but in general is a minor pathway for nutrient transfer. The actual pathway of nutrients into the root itself may be passive (no energy required; the nutrient enters with water) or active (energy required; the nutrient is moved into the root by a "carrier" molecule or ion)


CEC is defined by measurement of the amount of positively-charged ions (cations) which can be bound by a given weight of soil. Cations bound on the soil surface can exchange places with cations in the soil solution, making them available to the plants and subjecting them to leaching. Examples of cations include: K+, Ca2+, Mg2+, NH4+, Cu2+, Fe2+ or Fe3+, Mn2+, Al3+, Zn2+ A larger CEC implies a greater capacity to retain K+, Ca2+, Mg2+, and NH4+. Soils with large CEC are typically high in clay minerals and soil organic matter (OM), which have a lot of negative charges. CEC increases with pH, due to variable charge on the organic matter; the CEC measured at the pH of the soil is called the effective CEC. The CEC is calculated from exchangeable cations, and is only seldom measured in a soil testing lab. Low CEC means that fewer nutrients can be held by the soil, implying a need for more frequent nutrient additions. As CEC increases, more nutrients are attached to soil particles, and fewer remain in the soil solution. Since the nutrients in soil solution are available to plants, this means that while there are plenty of nutrients in the soil, the plants may not be able to take advantage of them. At the same time, they are less likely to leach. Addition of cations to the soil, through precise fertilization, will release cations into the soil solution as the new cations swap places on the CEC.



    Soil Doctors

    By Soil Doctors 28 Nov, 2017

    Water is the driving force of all nature.

    “Hydrophobicity” ( Hydro  meaning “water”  phobic  meaning “fear”), is the physical property of a molecule that is repelled from water - a molecule known as a Hydrophobe . A classic example of a hydrophobe is oil - it will not mix with water. Hydrophobic soils contain hydrophobes and resist moisture penetration. Hydrophobes are organic molecules and are very common in our environment.
    They are found in soils as the result of naturally decomposed plant tissues, microbial by-products, naturally occurring waxes and resins, and organic matter such as those found in mulches and potting mixes.

    Hydrophobicity develops in soils when hydrophobes surround the soil particle forming a waxy coating, or intermix with minerals currently in the soil. Moisture migration through hydrophobic soil is irregular and non-uniform. The soil does not wet and water runs off or moves through fissures and cracks.

    Water is the key to life on earth. Liquid H2O is at the heart of all ecosystems and access to water can determine the survival of an organism. Ensuring water reaches the roots of plants is essential and the primary process from which all others follow.

    Movement of water is affected by three forces;

    1. GRAVITY  - Constant downward pull

    2. COHESION  - The attraction of water molecules to each other   (the force that holds a water droplet together)

    3. ADHESION  - The force attracting water molecules to other   substances. (i.e. soil)

    In hydrophobic soil, the hydrophobes disrupt adhesion and the cohesive force is stronger. Water molecules 'bead' together, resisting the soil and running off with the force of gravity - down gradients or through cracks. When soil is hydrophobic, action is required reduce the cohesive forces and allow water to 'stick' to the soil again .

    Even minimal levels of water repellency can negatively impact water movement in soils, resulting in preferential flow/channeling patterns that encourage nutrient leaching and non-uniform distribution of applied water and input chemicals. This reduced effectiveness of water movement and poor distribution of fertilizer and chemical inputs can result in reductions in plant growth and vigour, as well as crop yield and quality.

    By Soil Doctors 27 Nov, 2017

    Plants take up the majority of their nutrient needs from the soil by utilizing different transport mechanisms. Different characteristics of soils affect their nutrient-holding capacity and which mechanisms work best. Some macronutrients, particularly nitrogen and phosphorus, cycle between residency in the soil, usage by plants, and air- and water-borne particles. These have important environmental effects, and the actions of these cycles influences management.

    The soil solution is the liquid in the soil. Plant nutrients (solids and gases) dissolved in the soil solution can move into the plant as the water is taken up by the roots. This is the medium through which most nutrients are taken up by the plant. Cations are positively-charged ions (such as Ca2+, Mg2+, K+, and NH4+) which are held on anionic (negatively-charged) exchange sites in the soil. Cation Exchange Capacity (CEC) is a measure of the amount of cations that can be held by the soil and released into the soil solution. Soils with a greater cation exchange capacity are able to hold onto more nutrients. Soil organic matter refers to hydrocarbon compounds in various stages of decomposition. Humus is organic material resistant to further decomposition, and which does not supply many nutrients. It can cause a negative charge in the soil, increasing CEC.

    Mineralization is the conversion of a nutrient from the organic (i.e. bound to carbon and hydrogen) form to the inorganic form. The process occurs when organic materials, such as soil organic matter, manure, plant residue, or biosolids, are decomposed by soil microorganisms. The nutrient is released, and is available for uptake by new plants. Immobilization is the reverse process of mineralization, wherein nutrients are converted from the inorganic to organic forms (i.e. taken by soil microbes and incorporated into their cells), making them unavailable to plants. Nutrient uptake antagonism refers to the competition between nutrients for uptake by plants. The two nutrients, often ions with the same charge, are said to be antagonistic with regard to the other. Some examples include


    • Phosphorus Excess Can Lead To Reduced Zinc Uptake
    • Calcium Excess Can Cause Boron Or Magnesium Deficiencies
    • Potassium Excess Has Been Found To Reduce Magnesium Uptake And Vice Versa

    Mass flow is the movement of dissolved nutrients into a plant as the plant absorbs water for transpiration. The process is responsible for most transport of nitrate, sulfate, calcium and magnesium. Diffusion is the movement of nutrients to the root surface in response to a concentration gradient. When nutrients are found in higher concentrations in one area than another, there is a net movement to the low-concentration area so that equilibrium is reached. Thus, a high concentration in the soil solution and a low concentration at the root cause the nutrients to move to the root surface, where they can be taken up. This is important for the transport of phosphorus and potassium. Root interception occurs when growth of a root causes contact with soil colloids which contain nutrients. The root then absorbs the nutrients. It is an important mode of transport for calcium and magnesium, but in general is a minor pathway for nutrient transfer. The actual pathway of nutrients into the root itself may be passive (no energy required; the nutrient enters with water) or active (energy required; the nutrient is moved into the root by a "carrier" molecule or ion)


    CEC is defined by measurement of the amount of positively-charged ions (cations) which can be bound by a given weight of soil. Cations bound on the soil surface can exchange places with cations in the soil solution, making them available to the plants and subjecting them to leaching. Examples of cations include: K+, Ca2+, Mg2+, NH4+, Cu2+, Fe2+ or Fe3+, Mn2+, Al3+, Zn2+ A larger CEC implies a greater capacity to retain K+, Ca2+, Mg2+, and NH4+. Soils with large CEC are typically high in clay minerals and soil organic matter (OM), which have a lot of negative charges. CEC increases with pH, due to variable charge on the organic matter; the CEC measured at the pH of the soil is called the effective CEC. The CEC is calculated from exchangeable cations, and is only seldom measured in a soil testing lab. Low CEC means that fewer nutrients can be held by the soil, implying a need for more frequent nutrient additions. As CEC increases, more nutrients are attached to soil particles, and fewer remain in the soil solution. Since the nutrients in soil solution are available to plants, this means that while there are plenty of nutrients in the soil, the plants may not be able to take advantage of them. At the same time, they are less likely to leach. Addition of cations to the soil, through precise fertilization, will release cations into the soil solution as the new cations swap places on the CEC.



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