Agriculture Reference
In-Depth Information
new-generation fertilizers have applications to crop production on long-duration
human missions to space exploration (Lal
2008
). Recently, Subramanian and
Sharmila Rahale (
2013
) have monitored the nutrient release pattern of nano-
fertilizer formulations carrying fertilizer nitrogen. The data have shown that the
nano-clay-based fertilizer formulations (zeolite and montmorillonite with a dimen-
sion of 30-40 nm) are capable of releasing the nutrients particularly N for a longer
period of time (
500 h). Subramanian and
Tarafdar (
2009
) suggested that clay particles are adsorptive sites carrying reservoir
of nutrient ions. Major portion of nutrient fixation occurs in the broken edges of the
clay particles. Zero valence nanoparticles adsorb onto the clay lattice, thereby
preventing fixation of nutrient ions. Further, nanoparticles prevent the freely mobile
nutrient ions to get precipitated. These two processes assist in promoting the labile
pool of nutrients that can be readily utilized by plants. Fertilizer particles can be
coated with nano-membranes that facilitate in slow and steady release of nutrients.
This process helps to reduce loss of nutrients while improving fertilizer use
efficiency of crops.
>
1,000 h) than conventional fertilizers (
<
3.2 Synthesis of Nano-fertilizers
Nano-fertilizers are synthesized by top-down (physical) or bottom-up (chemical)
approaches. Top-down approach is a commonly used method. In top-down
approach, the adsorbent or substrate used for synthesis of nano-fertilizers such as
zeolite or any other carrier is ball milled for several hours to achieve nano-
dimension. Usually, natural zeolite measures a range of 1,000-3,000 nm, and
grinding using high-energy ball mill reduced the size of the particles. Manikandan
and Subramanian (
2014
) reported that the ball milling of zeolite at 1, 2, 4, and 6 h
had reduced the dimension 1,078, 475, 398, 357, and 203, respectively. The size
reduction closely coincided with the increase in the surface area of 41, 55, 72, 83,
and 110 m
2
g
1
. Such phenomenal increase in the surface area provides extensive
surface area for nutrient adsorption and desorption. Despite the physical method of
nanoparticle synthesis is very simple, the product is heterogeneous and particles
often get agglomerated. To prevent agglomeration, stabilizing agents such as poly-
mers or surfactants are used.
The studies on slow-release fertilizers (SRFs) based on zeolites are limited to
nutrients, which can be loaded in cationic forms such as NH
4
+
and K
+
. However, if
the nutrients are in anionic forms such as SO
4
2
,NO
3
, and PO
4
3
, the loading is
negligible on unmodified zeolites. Therefore, it is imperative that the material
should have adequate affinity for anions so that the anionic nutrients can be
efficiently loaded for its use as SRFs. Anionic properties can easily be imparted
on the zeolitic surface using the concept of surface modification using surfactant.
Surface modification facilitates the loading of anion into the zeolite
s surface by the
anion exchange process. Haggerty and Bowman (
1994
) reported that surfactant-
modified zeolite (SMZ), a type of inexpensive anion exchanger has been shown to
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