Geoscience Reference
In-Depth Information
Fig. 11.3
Liebig's barrel
demonstrates his Law of
Minimum that declares the
element in minimal supply
decides the crop growth
defi cit
not enhance desired growth if non-nutrient growth-limiting factors are active. From
nutritional aspects, the primary difference between manufactured and organic soil
fertilizers is the speed at which nutrients become available for plant use. The release
of nutrients from manufactured fertilizer usually takes a few days to weeks. Nutrients
released from organic fertilizer become available over a period of months or years.
Recognition of this difference is critical when farmers use commercial fertilizers.
If the application of commercial fertilizers is high, a lot of fertilizer is washed out
by rain or by irrigation water especially with fl ood or furrow irrigation systems.
These excessively leached fertilizers subsequently appearing in rivers, lakes, and
sea gulfs support the rapid growth of both microorganisms and macroorganisms like
algae. When they die, their bodies are attacked and decomposed by bacteria. As
bacteria consume all of the oxygen dissolved in these waters for their activity, a lot
of half-decomposed or non-decomposed bodies remain that provide an opportunity
for the development of microorganisms adapted to the absence of oxygen. However,
the products of their reduction action are toxic for fi sh and not acceptable for
humans. Acidic conditions evolve, the pH decreases, and the acidity of the soil
increases. It is understandable that overloading surface waters with fertilizers is
ecologically harmful. We are going to describe it in more details in the next chapter
at the end of the paragraph dealing with phosphorus. Pollution of groundwaters by
fertilizers is less frequent, but if detected, it is a defi nite signal that the groundwater
could be polluted by microorganisms and should not be pumped and used in water
supplies.
