Agriculture Reference
In-Depth Information
Keywords
: Environment, erosion, organic matter, plant growth, soil microbes,
topsoil properties.
I
NTRODUCTION
Soil is a medium with some interesting properties suitable for plant
growth and microbial activities. Soil is formed and developed with time as
affected by different soil factors including the preliminary material, climate,
time, topography and biological activities. The soil producing factors singly or
combined produce the surface layer of the earth, or soil which is subjected to
different parameters. For the production of just one centimeter of soil a few
hundred years is necessary. This is why soil is considered a valuable source
and adequate efforts must be made to maintain it (Soil Survey Staff, 1999).
The soil producing factors determine the type of soil and its related
properties. Because a soluble environment is necessary for chemical and
biochemical processes in soil, with increasing the soil moisture the rate of such
processes increase, soil becomes more developed and soil horizons are formed.
Soil horizons are characteristic to each area and are used to classify soils (Soil
Survey Staff, 1999). Climate is also a very important factor for soil
classification. Accordingly, soils in humid and temperate climates are more
developed related to the soils in the arid and semi arid areas.
Soils in temperate area are the most productive soils for plant growth and
microbial activities. They are almost high in organic matter (3-4%) with
adequate amount of rain. In such areas soil structure, which is the way by
which soil particles or aggregates are bound, is appropriate for plant growth,
positively affecting yield production. Under dry climates, because of rain
deficiency, soils are very young and are not developed. However, in humid
area with high amounts of precipitation, soils become very developed and less
fertile related to the soils in temperate area.
Top soil, which is the surface soil layer, is the most fertile layer of the soil
with numerous processes and interactions. It is because most of soil organic
matter is accumulated in top soil as a result of returning plant residue, and
hence more microbial activities and appropriate soil structure is resutled. After
seeding, seedlings absorb their necessary nutrients from this part of the soil
and grow. Soil organic matter (SOM) can significantly affect soil properties
and hence yield production. Soil properties influenced by SOM include
microbial activities, soil nutrients, soil structure and porosity, cation exchange
