Agriculture Reference
In-Depth Information
cm soil, as a valuable source, a few hundred years is necessary; the process of
erosion must be controlled (Evans, 2005; 2006). There are different methods
by which soil erosion can be controlled including the use of dams, growing
plant, adding organic matter to the soil, and using mulch.
T
OPSOIL AND
P
LANT
G
ROWTH
As previously mentioned, topsoil is a suitable environment for plant
growth and microbial activities. The previously mentioned unique properties
of soil make plant growth and yield production likely. The presence of plants
in soil can considerably affect soil properties. The extensive root network is
able to grow into soil pores and attach soil particles affecting soil structure
(Fan et al., 2001, Bais et al., 2006; Badri and Vivanco, 2009).
Soil structure can affect many soil properties including physical, chemical
and biological ones. Air and water movement in soil is affected by soil
structure. Soil structure can also affect soil chemical properties including the
oxidation of organic matter as well as soil CEC. In addition, soil microbial
activities are also influenced by soil structure.
Seeds are planted in the soil surface layer or top soil. The established plant
is continuously interactive with its surrounding soil environment by the growth
of its roots through soil particles and the production of different compounds.
Plant roots can affect soil structure as they are able to bind soil particles and
aggregates. In additions, plant roots can influence soil properties by production
of their exudates (Haichar et al., 2008; Metlen et al., 2009).
The root exudates contain different products including organic and
mineral acids as well as nutrients. Such products make the environment around
the plant roots (rhizosphere) biologically very active, because such products
can act as nutritional sources or secondary metabolites for soil microbes
(Ramos et al., 2000; Kuzyakov et al., Micallef et al., 2009). The effects of
plant species on the rhizosphere determine the related microbial combination
(Miethling et al., 2000; Sharma et al., 2005; Haichar et al., 2008; DeAngelis et
al., 2009).
Secondary metabolites are produced at much less amounts relative to the
nutritional sources such as organic acids and nutrients; however they can
profoundly affect the biological population of rhizosphere (Knee et al., 2001;
Fan et al, 2001; Weir et al., 2004). It is because secondary metabolites can act
as signal molecules affecting the interaction between soil microbes and plant.
For example, there are flavonoids and/or Myc factors in secondary
