The soil is the stomach of the plant [Schriefer, 1984].
As plants do not have an internal digestive system they depend on external digestion [by microbes] and
absorption of nutrients by the roots [or foliage] [Schriefer, 1984]. The soil house and its tenants
[microbes] act as a substitute for the stomach of the plant.
Plants take up soluble salts, but in a healthy soil, soil microbial digestion [similar to a cow's or
sheep's rumen] occurs with microbes predigesting organic matter in order for the plants to recycle it.
Plants can also cultivate different micro-organisms around their rhizosphere by regulating root exudates.
Plants feed in four "Official chemical" ways:
Root nutrient uptake methods:
- Foliar [Feeding through the leaves]
Root Mass flow = Movement of ions in solution
- Mass flow [Suck it] Day time[?]
- Diffusion [Concentrate it, causing an "updraft"]
- Root interception [Swap it] Night time[?]
The plant's root system takes up soil water and soluble nutrients as though the plant has a straw in the
soil medium and sucks it up. The plant creates a lower water pressure in the root and the water is sucked
towards the root. Calcium and magnesium and to a lesser extent nitrogen and sulfur are taken up by mass
flow. Hydroponics relies mostly on mass flow of dissolved nutrients.
Root Diffusion = Movement of ions from a high to low concentration of nutrients
As a plant's root absorbs nutrients from the soil it creates a "sink" or vacuum or as Schriefer 
suggests an up draft which nutrients move into. Nutrients [ions] in areas of high concentration in the
soil solution migrate to where the lower concentration of elements exist due to the plant root removing
them. Most of a plant's phosphorous and potassium uptake moves to the root by means of diffusion.
Root interception = Contact exchange of ions
As new roots grow they come in contact with "new" soil and intercept or seize nutrients by exchanging plant
exudates for ions on soil colloids i.e. humus and clay [both negatively charged]. Root interception is most
active when plants are actively growing because as plants come in contact with, and are exposed to, a
progressively larger soil surface area, the plant can swap or exchange ions / nutrients.
Ion exchange occurs when the root exudes for example hydrogen which leaves the root and is attached to a
soil colloid. As the hydrogen separates from the root it leaves a negative charge on the root surface.
Therefore, the positively charged cations like Calcium, Potassium, Zinc and Copper are electrically attracted
to the root. Similarly, plants roots can also release negatively charged anions which leave vacant positive
charges on the root's surface, which in turn attract anions like Boron and Phosphorous. As you can see
plants to a point select what elements they require but this does not happen as efficiently when water
soluble fertilisers are used as the plant by mass flow literally has to take them up as it "drinks"
up water [and the soluble nutrients].
The chemistry of the soil can be thought of as the service to the soil house and will dictate which
tenants live there.
We will now go further and start to explore our soils by looking at soil chemistry, which can also
greatly influence the physical and biological nature of the soil.
The subject of soil chemistry involves the investigation of identifying the different elements in a
soil and how they influence that soil.
Your soil is "full" of elements which can be divided into positive and negative elements:
The elements that have a positive [+] charge are collectively called cations ["cat irons"].
There are other elements that have a negative [-] charge and they are
collectively called anions ["an irons"]. For example:
Poor soils are full of the wrong balance of elements.
They have an excess of some elements and a deficiency of other.
For example in an acid soil there is an excess of Hydrogen. In an alkaline soil there is often an
excess of two of the three dominant cations being Calcium [Calcareous soil], Sodium [Saline soils]
and Magnesium [black or grey pug clay if high sodium].
Productive healthy soils are full of the correct balance of elements.
So to correct a poor soil and improve the health of the plants and animals we need to duplicate or
copy the soil element balance found in productive healthy soils. We can do this by adding or changing
the availability of the needed elements.
Dr William Albrecht together with other scientists found that a good soil should have over
95% of the available elements as cations on the Base Saturation Percentage! These cations were needed
within certain ranges. The Albrecht cation balance model can act as an international benchmark to assess
how close your soil is to a chemically balanced soil. So to correct a poor soil we need to duplicate or
copy the required soil element balance that nature requires for each group of plant species that we wish
Our challenge is to work in harmony with nature to provide the correct chemical balance for the
plants that we grow [without forgetting the biological and physical requirements of the soil].
The information contained in this publication has been formulated in good faith, the contents do
not take into account all the factors which need to be considered before putting that information
into practice. Accordingly, no person should rely on anything contained herein as a substitute for
specific professional advice.
S.O.S. Rev 9.2 All rights reserved.
Contact: www.healthyag.com © Gwyn Jones 2001
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