Agriculture Reference
In-Depth Information
11.2 Stresses Occurring in Soils
Soil can be defined as upper layer of earth where plant grows and have their roots
(Brady
1974
). Soil indeed is the habitat for both microscopic (millions of microor-
ganisms) and macroscopic (insects, animals, plants) life (Pelczar et al.
1993
; Saika
2013
). The plants along with soil inhabiting microbes affect the soil structure,
fertility, and porosity; prevent erosion; and serve as source of organic matter;
likewise, any alteration in soil influences these life-forms. Soil stress is one of the
abiotic factors and can be defined as environmental variables affecting soil, which
can induce potentially injurious effects on the growth and yield of plants. Stress in
plants is mainly measured in relation to survival, growth, crop yield, biomass, and
primary assimilation processes associated with growth (Oliveira et al.
2013
). These
abiotic stresses also reduce the number, activity, and diversity of soil microflora,
which in turn may limit the crop production (Sgroy et al.
2009
).
11.2.1 Types of Soil Stresses
Soil stresses involve drought stress (decreased water availability to plants), salt
stress (increase salts in soil solution), heavy metal stress (excessive toxic metals in
soil), nutrient stress (insufficient nutrients in soil), and temperature stress (extremes
of temperature both high and freezing). Of these, drought is one of the most
important stresses followed by salinity stress (Kinje
2006
; Carmen and Roberto
2011
). Extensive areas of land are affected by these two stresses and are reported to
have maximum deleterious effects on the agricultural productivities (Oliveira
et al.
2013
). The effects of drought and salt stress are highly interrelated and
influence practically almost every aspect of plant. The effects of stresses on plants
involve disrupted photosynthesis leading to leaf senescence, accumulation of
excessive reactive oxygen species (ROS), nutrient deficiency, and destruction of
cellular organelles and metabolism leading to decreased plant growth. The after-
effect includes both physiological and metabolically disturbed homeostasis of plant
(Carmen and Roberto
2011
; Oliveira et al.
2013
). Metal stress is another important
soil stress, which is becoming increasingly intensive due to numerous anthro-
pogenic factors (Glick
2010
). Unchecked increase in population and industrial
revolution is resulting in accumulation of toxic metals and organic wastes in soil
making it unsuitable for agricultural practices and also harmful to all life-forms
(Glick
2010
). Some of the effects of these stresses are briefly outlined in Fig.
11.1
.
11.2.1.1 Drought Stress
Water comprises 80-90 % of the plant biomass and plays central role in all major
physiological processes of the plants involving nutrient uptake and photosynthesis.
