Agriculture Reference
In-Depth Information
conventional water-soluble agrochemical (fertilizer or pesticide) with an insoluble
or poorly soluble protective layer that controls water penetration and, thus, the
dissolution rate in order to synchronize the release and the consumption rates of the
medium (Trenkel
2010
). Among the most likely investigated systems are polymer
composites, where agrochemicals are embedded within the matrix that hinders the
diffusion of nutrients to the environment. In order to ensure the expected release
reduction, it is usually necessary to have a large amount of host matrix (about 40 %
or greater). However, formulations with only small amounts of active compounds
are possible (Trenkel
2010
). These limitations have motivated several studies on
improving the performance of slow- or controlled-release systems based on poly-
meric composites or nanocomposites.
Therefore, some of the main recent advances in research concerning the appli-
cation of nanocomposite materials in slow or controlled release of agrochemicals
are reviewed in this chapter, emphasizing their application and prospects.
11.2 Controlled- or Slow-Release Systems Applied
to Fertilizers
Plants require various nutrients for their growth and development, some in higher
amounts (classified as macronutrients) and others in lower amounts (classified as
micronutrients). The group of macronutrients is composed of nitrogen (N), phos-
phorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). Carbon
(C), hydrogen (H), and oxygen (O) are also considered macronutrients, but they are
available in large quantities in the environment and are directly assimilated by
plants. The group of micronutrients is composed of boron (B), chlorine (Cl), cobalt
(Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and
zinc (Zn) (Finck
1992
). All these nutrients, if not available in sufficient amounts in
soil, can be provided by fertilizers.
Fertilizer is any organic or inorganic material from natural or synthetic origin
(except limestone) that is added to soil to supply one or more essential nutrients for
normal growth and development of plants (Glossary of Soil Science Terms
2008
).
Nowadays, fertilizers are essential for obtaining high levels of agricultural produc-
tivity. Nitrogen stands out among the macronutrients that are mainly applied in soil
management for different crops. It is required and applied in large quantities in the
composition of various fertilizers. Data presented by the Brazilian Association for
Promotion of Fertilizers (ANDA) in 2013 show that from 1990 to 2011, the
consumption of nitrogen in Brazil increased nearly 275 %, from 0.8 to 3 million
tons.
Despite nitrogen presents as one of the most abundant structural elements in
living beings, it only ranks as the 17th element that composes the Earth
s crust. In
the diatomic molecular form (N
2
), it is the major component of the atmosphere, but
this state is a chemically inert compound that reacts only with great expenditure of
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