Basically I focused on Soil and its various properties and importance and so on.

1. Short Presentation
on Soil
Presented by,
Md. Galib Ishraq Emran.
Department of Environmental Sciences.
2015-16 Sessions.
Registration No: 41778.
Class Roll: 219.
Jahangirnagar University,
Savar, Dhaka-1342.
Email: mdgalibishraqemran@gmail.com

59. Water Table

60. Soil Matrix

62. Soil Aeration
Soil aeration is phenomenon of rapid exchange of
oxygen and carbon dioxide between the soil pore
space and the atmosphere, in order to prevent
the deficiency of oxygen and/or toxicity of carbon
dioxide in the soil air. The well aerated soil
contains enough oxygen for respiration of roots
and aerobic microbes and for oxidation reaction
to proceed at optimum rate.

63. Factors Affecting Soil Aeration
(i) Soil organic matter:
When organic matter is added to the soil, it is readily
decomposed by the soil micro-organisms to liberate the
carbon dioxide content of the soil air.
(ii) Since the top soil contains much more macrospore space
than the subsoil, the opportunity for gaseous exchange is
more in top soil than in the sub soil. Hence the oxygen
content of the top soil is greater than that of the sub soil.
(iii) Soil moisture:
The macrospores are filled up with water immediately after
heavy rain when the oxygen content falls to near zero.
When the soil is artificially drained again, the macrospores
are filled up with air and the oxygen content of the soil
increases.

65. Importance of Soil Aeration
• Soil aeration affects the availability of some nutrients elements to plant roots. Manganese and iron occurs in the well aerated soil
in their higher valent forms (Mn++++, Mn+++, Fe+++) and in poorly aerated soils in their lower valent forms (Mn++, Fe++). They are
available to plants only in their lower valent forms.
• Crops suffer from manganese toxicity if an excessive amount of manganese occurs in the soil in the soluble form. Manganese
toxicity to plant roots, under this circumstance, may be corrected either by making the soil more aerated by tilling the soil and
improving drainage of the soil or by increasing the soil pH by applying lime to the soil.
• When iron and manganese are in short supply to the soil, then the soil may be subjected to anaerobic condition by applying
readily decomposable organic matter to it.
• Carbon dioxide would be produced from the decomposition of organic matter to make the soil relatively more anaerobic when
manganese and iron will be reduced from their respective higher Volant (Mn++++, Mn+++, Fe+++) forms to their respective lower
valent form (Mn++, Fe++) i.e. divalent forms and would be available to plant roots.
• Ferric phosphate would be reduced to ferrous phosphate. Carbon dioxide produced from the decomposition of organic matter
reacts with water to form carbonic acid which slowly dissolves insoluble phosphate. So the availability of phosphates (would be
increased to the plant roots.
• Sulphur occurs as sulphate in well aerated soil. Plant roots assimilate sulphate. Sulphate is reduced to sulphide in poorly aerated
(water logged) soils. Hydrogen sulphide is toxic to plant a root which suffers from it in water logged soil.
• Organic matter is decomposed by aerobic bacteria in well aerated soil when complex organic nitrogen and phosphorus
compounds are decomposed to their respective simple inorganic compounds which plant roots readily assimilate symbiotic and
non-symbiotic nitrogen fixation takes place only in well aerated soils.
• Nitrates are reduced to oxides of nitrogen and nitrogen gases in poorly aerated soils. These gases escape to the atmosphere, long
light coloured roots develop in well aerated soils. Root hairs develop best under well aerated condition.
• Roots get thicker, shorter and darker in anaerobic soils that also retard the development of root hairs. Poor aeration causes
abnormal development of roots, e.g. abnormal shaped sugar beet and carrot roots have been found in poorly aerated soils.
• Nutrient absorption is an energy consuming process. Energy is available from respiration is expended in absorbing nutrient ions
from the soil. Hence nutrient absorption is retarded in poorly aerated soils.
• If an excessive amount of readily decomposable organic matter has been added to the soil, then it would decompose to evolve
high amounts of carbon dioxide to the soil. Consequently root growth and germination of seeds would be adversely affected.
• Some crops become infested with pathogens in poorly aerated soils. The incidence of will disease caused by the fungus (Fusarium
sp) has been attributed to poor aeration. Citrus and suffers from die-back in poorly aerated soils have also reviewed the works of
some investigators who have observed that poorly aerated soils (waterlogged soils) has an effect on the pathogenicity of root
infesting fungi.