Agriculture Reference
In-Depth Information
observed that the use of materials (coated urea with resin or sulfur) provided better
results in all parameters than the commonly used fertilizers.
Gagnon et al. (
2012
), in a 3-year study (2008-2010) conducted in clay soil near
the city of Quebec, Canada, compared the effect of polymer-coated urea, urea with
nitrification inhibitor, dry urea, and urea/ammonium nitrate 32 %, on the yield of
corn cultivation, accumulated N in the plant, and NO
3
remaining at harvest soil.
The authors observed that the polymer-coated urea had superior behavior for two of
the three evaluated parameters, especially in wet years—suggesting that this mate-
rial can be an alternative for farmers in the fertilization of corn crops in eastern
Canada.
Li et al. (
2014
) investigated the benefits of slow-release fertilizer systems, in
potassium sources, by means of a material based on treated coal ash. In that study,
tests were made directly into the soil, where they observed that the slow-release
system contributed significantly to the development of crops.
Controlled- or slow-release systems can be prepared by (a) chemical modifica-
tion, usually organic nitrogen compounds, for example, condensed aldehydes with
urea, which are much less soluble in water than urea; (b) change in the physical size
of granular fertilizers, using much larger urea granules, usually called
supergranules (the combination of larger particle size with a deeper application of
fertilizer reduces loss by leaching and evaporation); (c) the use of inorganic
compounds with low solubility, such as metal ammonium phosphates (e.g., mag-
nesium ammonium phosphate (MgNH
4
PO
4
)), and partially acidified phosphate
rocks; (d) use of physical barriers, in which the fertilizer may be formatted as
tablets or coated granules (encapsulated) with hydrophobic polymers or minerals;
or (e) as matrixes in which the active soluble material is dispersed into a continuous
medium that restricts the nutrient dissolution.
Some products are already commercially available; for example, Basacote
®
and
Osmocote
®
refer to the surface coating of conventional granules, which provide a
solubilization barrier; however, when its rupture occurs, they lose their retention
efficiency. Thus, many studies have been conducted to develop new methods to
protect the agrochemicals, such as incorporation into a composite structure. Yang
et al. (
2013
) synthesized a bio-polyurethane from corn straw, isocyanate, and
diethylenetriamine, which was used to coat urea granules, in order to create a
controlled-release fertilizer. In the same study, a new superabsorbent compound
was also formulated from proteins of chicken feathers, acrylic acid, and
N
,
N
-
0
-methylenebisacrylamide and tested as outer granular coating for water retention.
The obtained materials were effective in reducing N losses by leaching and
increased retention capacity of water in soil when compared to the conventional
fertilizer tested. Figure
11.2
shows images of these new fertilizer materials and
cumulative nitrogen release rate of different coated fertilizers in water and soil.
Liang and Liu (
2006
) presented the preparation of a slow-release compound
fertilizer based on double-coated urea granules with poly(acrylic acid) (outer
coating) and polystyrene (inner coating). Tao et al. (
2011
) succeeded in preparing
a controlled-release nitrogen fertilizer which was able to retain water. However,
this was possible only with the triple-coated urea granule, being polyethylene as the
inner coating, superabsorbent poly(acrylamide-
co
-acrylic acid) as the medium
