SYNTHESIS, CHARACTERIZATION AND RELEASE OF NANO-ENABLED PHOSPHORUS FERTILIZER IN ACID SOILS OF ASSAM
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Date
2021
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Abstract
The study on “Synthesis, characterization and release of nano-enabled
phosphorus fertilizer in acid soils of Assam” was undertaken during 2019-21with the aim
to synthesize and characterize zeolite based nano P fertilizer and to study its release
pattern over 90 days of incubation in three different types of soil representing major soil
orders of Assam, taking recommended fertilizer dose applicable for maize. Surfactant
modification of the zeolite (SMZ) was done by using hexadecyltrimethylammonium
bromide (HDTMABr) as surfactant and subsequently, the slow-release fertilizer (SRF)
for phosphorus was synthesized by treating the SMZ with potassium dihydrogen
orthophosphate to prepare the P-loaded SRF. It was observed from the XRD pattern that
the zeolite framework had not undergone major structural change by the addition of
HDTMABr and the crystallinity of zeolite remained the same. The surface morphology
characterized by SEM, showed that the zeolite was of cubical geometry. The developed
zeolite based nano P fertilizer recorded an average particle size of < 100 nm. The specific
surface area of nano zeolite fertilizer (modified) was found to be less (90.07 m2/g) as
compared to unmodified zeolite (262.72 m2/g). The pore diameter was found to be in the
microporous (< 20 nm) range. Maximum adsorption of 7.4% added P was found in nanofertilizer
which was 60% higher as compared to unmodified zeolite. The incubation study
of P release in different treatments over the different types of soil witnessed marked
variations during the entire days of incubation. Although no definite trend was observed
in absolute control all throughout the incubation period, the lowest concentration of P
was found in 7 days of incubation in all the treatments. In treatment receiving
recommended dose of P through SSP, there was a gradual rise in available P
concentration, reaching the maximum peak at 32 days of incubation beyond which no
further increasing trend was observed. Relatively, the treatment receiving recommended
dose of P through nano-fertilizer had a gradual increase of P from 7 days upto 90 days of
incubation. A similar trend was also observed in nano treated P fertilizer receiving 2.5
times reduction, 5 times reduction, and 10 times reduction from the recommended dose.
However, the concentration of release was lower and found to be in decreasing order as
compared to recommended P level applied through nano P. Highest concentration of P at
90 days of incubation was found in recommended P applied through nano-fertilizer in the
silty clay loam soil (8.82 mg/kg), which was significantly higher than recommended P
applied through SSP (7.54 mg/kg). A significant difference was also noticed between
recommended dose of phosphorus applied through nano P (8.82 mg/kg) and treatment
receiving 2.5 times reduction of recommended P from nano P (6.38 mg/kg). The same
trend of P release was observed in the soil with clay loam and sandy clay loam texture.
The differences in clay content between the soils affected the P release pattern which
followed the order - Majuli (sandy clay loam) > Jorhat (silty clay loam) > Titabar (clay
loam).The first-order kinetic constant was found to increase from 0.096 μg/g/day in
recommended dose of P applied through SSP to 0.100 μg/g/day in treatment having a 10
times reduction of recommended P given through nano P in the silty clay loam soil. In the
case of second-order kinetics, there was a decrease in rate constant value (-0.015 to -
0.014 g/μg/day) which means an increase in the release of P. The rate constant of
parabolic diffusion equation was the highest in treatment receiving recommended dose of
P through nano-fertilizer (3.012 μg/g/day) in the silty clay loam soil. This increase in rate
constant was found in the clay loam and sandy clay loam soil also which indicated high
reactivity of the fertilizer. As observed from the R2 value, the parabolic diffusion
equation was found to be the best fit for describing the P release as compared to the other
two kinetic models.