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The Soil

One of the wonders of nature that has given this planet of ours life! A fertile soil of the correct type is vital for a plant to grow to it’s full potential.

Soil is weathered Rock, the Minerals of which are called: Sand, Silt and Clay. The names sand, silt and clay refer to their particle size. Sand particles are larger than the very small clay particles, with silt particles in between the two. The varying amounts of these particles determine the Texture of soil. By and large - what we get is what we keep! We can not substantially alter Soil Texture.

We can however, improve the Structure of soil. Soil Structure refers to the cracks and air spaces between the soil particles. Air is the ingredient that ultimately determines the health of soil. The gaps between the soil particles fill with water after steady rain. Soil that has a good structure, e.g. has been improved by digging, allows this water to drain away. If drainage is insufficient this water fails to drain away. As the water has driven out the air the soil becomes waterlogged. A soil high in Organic Matter will be fertile, remaining moist and cool for longer. Organic matter consists of dead and decaying vegetation, animals, insects etc. Soil organisms, (worms, fungi, bacteria etc) break the organic matter down to produce Humus.

Humus is a dark, sticky substance that is vital for the general health of soil. If water is present in the soil the humus dissolves and the nutrients are released in a form that plants can absorb. Annual applications of organic matter, even to a well structured and rich soil will help keep it fertile and with a good structure. The aim of improving the structure of any type of soil is to create what is referred to as Crumb Structure. This is where the soil particles bond together in small, clumps that break apart easily. The ideal soil has a balanced proportion of sand, silt, clay and Humus and is given the final expression used to describe soil - Loam.

The hand test determines Soil Texture. Squeeze a small amount of moist soil in the palm. Now roll a small lump between finger and thumb. If the soil feels...

Gritty and crumbles easily:
The soil is sandy

Gritty but does not crumble:
It’s a sandy loam

If the soil binds together and feels…
Silky or like soap:
The Soil is classed as Silt

Silky and breaks easily:
Indicates a Silty Loam

Sticky, shines when rubbed by the thumb:
Classes the Soil as Clay

Moist and breaks into smaller pieces as rubbed between thumb and finger:
This indicates the soil is a Clay loam

Clay Soils;
Wet, heavy, cold, hard to work but high in nutrients.

Sandy Soils;
Dry, light, warm, easy to work but leach nutrients, i.e. 'hungry'.

Silty Soils;
In between the two extremes.

If room allows, a compost bin or heap will be of great benefit to the garden. By composting down our own waste such as raw vegetable kitchen scraps, grass clippings, in fact any ‘green’ plant matter, we can produce the humified matter that can then be added to the soil.

There are about a hundred Chemical Elements on Earth, and at least seventeen of these are the Nutrients essential to plants. These essential elements can be divided into two groups:

Group One - Organic Elements
C – Carbon O – Oxygen H - Hydrogen
Derived from the atmosphere.

Group Two - Mineral Elements
Derived from rocks (See Below).

The Mineral Elements are divded into two nutrient sub-groups:

Major Nutrients:
N - Nitrogen
P - Phosphorous
K - Potassium
Ca - Calcium
Mg - Magnesium
S - Sulphur

Trace Elements:
Fe - Iron
Cl - Chlorine
Mn - Manganese
Zn - Zinc
Cu - Copper
Mo - Molybdenum
B - Boron

Major Nutrients: N, P, K are needed in large amounts by the plant. They are often supplemented by the use of fertilizers to improve growth and replace loss by harvest. Ca, Mg, S are needed in moderate amounts, sometimes deficient or unavailable to plants and then have to be added.

  Trace Elements: As essential to the growth and health of the plant as major elements, but needed in minute quantities. Most medium to heavy soils contain sufficient supply. As with all elements they are easily leached from sandy soils, so may need to be supplemented.  

The affects of the three major nutrients N. P. K. on plant growth:  

Nitrogen (N) aides stem and leaf growth. A deficiency shows as pale green or yellow foliage, small leaves and stunted growth.
Phophorous (P) aids root growth. A deficiency shows as dull bluish-green leaves with tints of bronze and purple, and poor root growth. Availability to plants easily affected by pH, especially a low pH.
Potassium (K) improves hardiness and quality of flowers and fruit. A deficiency is first seen in older leaves which turn bluish-green with a marginal leaf scorch.

There is a little Limerick to help remember the parts of a plant that benefit from N.P.K.
Shoots, Roots, Flowers & Fruits.

Before we finish this brief summary of the soil beneath our feet there is one more thing we need to look at - Ph.

Soil pH:
The pH stands for Puissance Hydrogen or Power of Hydrogen
Depending primarily on the bedrock, soils vary in;

• Acidity - soils over sandstone.
• Alkalinity - soils over limestone.

It is the pH of soil that influences the availability of nutrients to a plant, particularly with trace elements. The effect on plant growth of a chalk or alkaline soil can be very noticeable and even catastrophic on plants that need the opposite type of soil. Azaleas for example are well known advocates of an Acidic soil. They and others like them will suffer nutrient deficiencies, especially iron and manganese. The first signs are a yellowing of the leaves and growth will be very slow and stunted. It may take several years but in most cases the plant will succumb to growing in the wrong type of soil and die.

Acid soils are characteristic of moor-land and peat, on the other hand, when soil has pieces of chalk visible, and then it will be very alkaline.
A logarithmic pH scale has been devised to help establish a soils acidity. The units range from 0 to 14, with neutral being 7.0. Readings below this indicate increasing acidity and above pH 7.0, increasing alkalinity.
Pure water for example has a pH reading of 7.0 which is neutral. Below neutral is acid and above pH 7.0 - alkaline. Moderately acid soils for example have a reading of 6.0 and moderately alkaline soils, a reading of 7.5.

The normal range for British soils is between pH 4.0 and 8.5. At the very extremes of the range, plants have to be specially adapted to survive. Rhododendrons and heather for example require an acid soil of pH 4.5 to 5.5, whilst Clematis and yew prefer alkaline conditions of pH 7.5 to 8.0.
It is well worth if not essential, knowing the soils pH in a garden. Testing kits are readily available and are quick and easy to use. When using them, take random soil samples from around the garden and mix them together. Use this as your sample.

pH testing tube Testing kits are cheap, quick and simple to use, just follow the instructions supplied and try to use distilled water. The water will change colour once the soil has settled which determines your soil’s pH. A soil pH of 6.5 is ideal, as it suits the majority of plants.

 

 

 

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