CHEMICAL CHARACTERISTICS OF SOIL

 CHEMICAL CHARACTERISTICS OF SOIL

1. Macroelements in Soil

·       Macroelements are the most important nutrients for plants.

·       Macroelements occur naturally in the soil to some extent and can be supplemented with fertilizers, manure and compost.

·       Macroelements are Calcium (Ca), Magnesium (Mg), Potassium (K), Sulphur (S), Phosphate (P), Nitrogen (N) and Sodium (Na).

2. Microelements in Soil

·       Trace elements are nutrients that plants need in small doses.

·       The trace elements are Boron (B), Copper (Cu), Manganese (Mn), Cobalt (Co), Silicon (Si), Zinc (Zn), Iron (Fe) and Molybdenum (Mo).

·       Signs of shortage occur when the disappearance of trace elements through the crops is not compensated adequately with supplements by means of fertilizer, manure or compost, or when the availability of certain elements is limited by the pH or mineral imbalance in the soil.

·       Crop analyses can help to trace an acute shortage and to solve it at plant level.  

3. Soil Organic matters and Formation of Humus

·        Organic matter consists of dead plants, animal, microbes and fungi or their parts, as well as animal and microbial waste products in various stages of decomposition. Eventually, all of these break down into Humus, which is relatively stable in the soil. Humus is the organic component of soil, formed by the decomposition of leaves and other plant materials by Soil microorganisms.

·        Chemically, Humus contains following Organic molecules

a)     Amino acids - Glutamic acid, Alanine, Valine, Proline, Cystine and Phenyl alanine.

b)    Purines – Adenine and Guanine.

c)     Pyrimidines – Cytosine, Thymine and Uracil.

d)    Aromatic molecules

e)     Uronic acids - Glucuronic acid, Galacturonic acid and Lactic acid

f)      Aliphatic acids – Acetic acid, Formic acid and Succinic acid.

g)    Amino sugars – Glucosamine and N – Acetyl Glucosamine.

h)    Pentose sugars – Xylose, Arabinose and Ribose.

i)      Hexose sugars – Glucose, Galactose and Mannose.

j)      Sugar alcohols – Inositol and Mannitol

k)    Methyl sugars – Rhamnose, Fucose, 2-o-methyl D-xylose & 2-o-methyl D-arabinose.

l)      Other compounds - Fats, Oils, Waxes, Resins, Tannin, Lignin and Pigments.

·        In Soil, Organic matters are very important for

ü  Acts like glue that helps hold soil aggregates together.

ü  Helps to bind water with the soil and making it available to plants for uptake.

ü  Organic matter particles have a negative charge (Cation exchange capacity) and thus attract, hold, and release cations necessary for plant growth and reproduction.

ü  Organic molecules can bind up dome ions that are toxic to plants.

4. Soil Colloids

·       The word Colloid first coined by Grahm (1849) is derived from Greek words ‘kolla’ meaning glue and eoids meaning appearance, i.e., glue like in appearance. 

·       There are two types of Colloids in soil. They are

a)     Mineral colloids or Clay colloids

b)    Organic or Humus colloids

·       The Inorganic colloids occur as very fine particles and Organic colloids occur in the form of humus particles.

5. Soil Acidity

·       Acidity (pH) is a measure of the concentration of free Hydrogen ions (H+).

·       Soil acidity can be further divided into:

a)     Extremely acidic         -             pH less than 4.5

b)    Very strongly acidic  -             pH 4.5 to 5.0

c)     Strongly acidic             -             pH 5.1 to 5.5

d)    Moderately acidic       -             pH 5.6 to 6.0

e)     Slightly acidic               -             pH 6.1 to 6.5

f)      Neutral                             -             pH 6.6 to 7.5

6. Saline Soils

·       The salt level is the sum of all the mineral salts that are present in the soil.

·       Various salts can originate from the soil itself, fertilizer, organic manure and in coastal areas from salt marshes.

·       When the salt levels in the soil are higher than in the cells of the plant roots, the moisture is drawn from the roots and the fine hair roots die off. This results in the cause of reduced growth or death of the plant.

·       Crops vary in the extent to which they tolerate salt and the salt levels at which they can still provide a good yield.

·       Some crops grow well in salty soils.

7. Cation Exchange Capacity (CEC)

·       Cation Exchange Capacity (CEC) the amount of cations can be bound to the soil.

·       Soil particles have a net negative charge (anion), and so can attract positive ions (cations), hold them, and then release them to the soil water when its cations have been lost through leaching or plant uptake.

Cations such as Potassium (K⁺), Calcium (Ca⁺²), Magnesium (Mg⁺²), Iron (Fe⁺² and Fe⁺³), and Zinc (Zn⁺²) are essential plant nutrients, so the ability of soil to hold and release these ions later is important for plant growth and reproduction.