Geoscience Reference
In-Depth Information
waters of the rivers and lakes. As the algae die, they sink to the bottom where they
are decomposed, and the nutrients contained in organic matter are converted into
inorganic forms by bacteria. The decomposition process uses and depletes suffi cient
amounts of oxygen from the deeper waters to kill fi sh and other aerobic organisms.
The water becomes cloudy and murky having typical colors of a dark green, yellow,
brown, or red. Eutrophication also decreases the value of rivers, lakes, and estuaries
for recreation and fi shing. Health problems are especially critical when the contami-
nated water is used as drinking water for humans because adequate water treatment
is diffi cult to achieve. Up to now we described eutrophication as commonly caused
by human activities, but it can also be a natural process particularly in lakes and
reservoirs.
Potassium
, K, the third major plant and crop nutrient after nitrogen and phospho-
rus, has been used since antique times as a fertilizer applied to soils as water-soluble
salts containing potassium and called potash. The name derives from “potash,”
which refers to procedures known for obtaining soluble salts from plant ashes
soaked in a pot of water. Elemental potassium does not occur in nature due to its
violent reaction with water. Potash improves yield, nutrient value, taste, color, tex-
ture, and disease resistance of food crops. It has wide application for the production
of fruit, all grains, sugar, corn, soybeans, and cotton. General symptoms of potas-
sium defi ciency include chlorosis - the yellowing of leaves caused from a lack of
chlorophyll - followed by scorching that moves inward from the edges of the leaves.
Older leaves, affected fi rst, may crinkle and roll while shoots suffer shortened, zig-
zag growth. The excessive amounts could act harmfully in semiarid and arid zones
because of increased salinization.
The three remaining macronutrients are frequently called
secondary macronutri-
ents. Calcium
Ca is an essential part of plant cell walls. Their structure enables
transport and retention of all elements constituting the growth of the plant's body. If
calcium resides in soluble soil compounds, it acts against the accumulation of alkali
salts and balances the tendencies toward the acidifi cation of soils. Hence, its pres-
ence in a soil is highly benefi cial for the great majority of cultivated plants.
Accordingly, liming is a very effective tool against acidifi cation, especially after the
drainage of waterlogged soils. As we have shown in Sect.
11.1
,
Magnesium
Mg
forms the part of chlorophyll in green plants that is necessary for photosynthesis and
growth of plants. Consequently, whenever magnesium sources in soils are inade-
quate, dolomite liming or the application of fertilizers containing Mg is a common
agricultural practice.
Sulfur
S is essential for production of proteins in plants and for
enzyme activity as, e.g., related to photosynthesis. It improves the growth of roots
and seeds and enhances the resistance of plants against rapid changes of meteoro-
logical conditions.
Micronutrients act in individual processes and their role differs in relation to
individual types of plants. Their many special roles are described primarily in aca-
demic literature.
Bioenergy has to be mentioned when we deal with nutrients. Nowadays, a huge
advocacy and trend of industrial-scale harvesting of biomass for bioenergy
production exist owing to political, pseudoscientifi c, and short-term economic