Agriculture Reference
In-Depth Information
nanocomposite structures, improving the thermal stability and mechanical proper-
ties of a bulk material. In the case of these fertilizers, they are typically employed as
a medium for the adsorption of the nutrient product. Within the nanosized interlayer
space, fertilizers could be protected from decomposition by sunlight, heat, and
microbes, minimizing fertilizer loss. Furthermore, strong adsorption within the
clays would attenuate losses through leaching as well as allow for the slow release
of the fertilizer. For example, in a study by Park et al., the intercalation of a
magnesium-urea complex into the nanoscale interlayer space of montmorillonite
clay was found to protect the urea from rapid degradation in soil, which could serve
to improve nitrogen use efficiency (Park et al.
2004
). Numerous patents have been
filed exploiting the use of clays as nanoscale hosts for fertilizer products. Zeolites
alone (Guo
2007
;Yu
2005a
; Wu and Wu
2010
; Gai et al.
2011
) or doped with
nanoparticles (Vempati
2008
) have been loaded with plant nutrients and found to
increase fertilizer use efficiency. Similarly, the nanoscale pores and channels in
palygorskite (also known as attapulgite) (Cao et al.
2007a
,
b
,
c
,
d
), kaolin (Zhang
et al.
2005b
), and a Chinese clay known as Ximaxi (Li et al.
2002
) have all been
exploited for strong adsorption of fertilizers and the slow release of fertilizer from
the matrix.
Fertilizer could also be coated on nanoparticles or housed in nanotubes. Metal
nanoparticles, e.g., Ag, have been investigated as carriers for plant nutrients
(Nilanjan
2013
). Halloysite nanotubes deserve special mention separate from the
discussion on the other clay materials. Halloysite nanotubes are hollow clay tubes
formed by surface weathering of natural aluminosilicate minerals. The tubes have
diameters that are typically less than 100 nm and lengths that range from about
500 nm to over 1.2
m. They can be filled with any agent to allow for its extended
release. A recent patent held by the company NaturalNano, Inc., has utilized these
nanotubes as hosts for fertilizers (Price and Wagner
2008
;
http://www.naturalnano.
com
, accessed January 10, 2014). Hydroxyapatite (HA) nanoparticles have been
investigated in patents (Wei et al.
2011
); Kottegoda et al.
2011a
,
b
;
2013
) and
papers (Kottegoda et al.
2011c
) as a carrier for fertilizer (see Fig.
2.6
). Urea-
modified HA nanoparticles that were sequestered in the cavities of
Gliricidia
sepium
wood exhibited much slower release profiles in soils of three different pH
values (4.2, 5.2, 7) and were releasing
μ
10 mg a day even by day 60, unlike the
faster release that was noted for a conventional fertilizer. Control experiments with
the conventional fertilizer housed within the wood would help to parse out the
effect of the nanoparticle carriers on the release profile of the urea.
Nanotube fertilizer carriers have also been prepared using cochleate structures.
Cochleate delivery vehicles are stable, nanoscale phospholipid-cation nanotubes.
They have a multilayered structure consisting of a large, continuous, solid lipid
bilayer sheet rolled up into a spiral. These structures provide their contents with
improved solubility as well as protection from environmental conditions. When
used in drug delivery, they deliver their contents to target cells through the fusion of
the outer layer of the cochleate to the cell membrane (Gould-Fogerite et al.
2003
).
Small cochleate structures can possibly be taken in through the stomata of plants,
allowing for improved delivery of fertilizer, pesticides, etc. Nanoscale cochleate
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