Agriculture Reference
In-Depth Information
(CEC). CEC is a very important soil property affecting many processes in the
soil. The exchange of nutrients between the phases of soluble and
exchangeable can control soil pH fluctuations, which is of great significance
for the activity of plant and soil microbes (Parfitt et al., 1995).
In case of increasing nutrients concentration in soil solution, for example
by fertilizing soil, and according to stochiometric balance a part of nutrients is
absorbed on the particles surface. As a result the balance between the solution
and exchangeable phases is maintained and soil pH remains unchanged. When
the concentration of nutrients is decreased, for example as a result of nutrient
absorption by plant roots or by soil microbes a part of soil nutrients is released
into the soil solution. Accordingly, a balance between the two sides of the
reaction is made keeping soil pH constant. This is called soil buffering
capacity or the ability of soil to resist versus pH fluctuations. This is the
property of soil colloids including soil organic matter and soil clay particles.
Hence, in a soil with higher rate of colloids, higher CEC and hence higher soil
bufferic capacity is resulted (Parfitt et al., 1995).
SOM can also significantly affect soil microbial activities. It is because
SOM is a source of food for soil microbes as it is high in nutrients. Soil
microbes as a very important component of ecosystem are able to decompose
organic matter and hence recycle it. Accordingly, by the mineralization of
SOM, energy recycling and the reuse of nutrients, by plants and soil microbes
(Nannipieri et al., 2003), becomes likely. For example, there are soil
ammonifying and nitrifying bacteria, turning organic N into ammonia (NH
4
+
)
nitrate (NO
3
-
), respectively. This mineral N is a very important source of N for
crop plants and soil microbes, especially in areas with high rate of organic
matter (Miransari and Mackenzie, 2010, 2011a,b).
The other important effect of soil organic matter is on climate resulting in
global warming. Atmospheric CO
2
, as a product of plant root and soil
microbial respiration, can significantly affect climate and hence the globe
(Fang et al., 2005b; Wutzler and Reichstein, 2008). It is because CO
2
like
other greenhouse gases including methane and N oxides can reflect the heat
energy emitted by the earth resulting in the warming of globe. Hence the,
sequestration of C in soil in form of organic compounds can be a major factor
affecting the atmospheric climate. In other words transformation of C between
soil and atmosphere is controlled by the presence of organic matter in soil
including the decomposing organic matter, plants and soil microbes (Lal,
2002; Post et al., 2004). The sourcs of CO
2
emission from soil are root, plant,
SOM, rhizosphere and soil microbes (Kuzyakov, 2006).
