M Sc

The study entitled “Sorption and movement of cyantraniliprole in sandy loam soils
with and without organic amendments” was conducted in the Department of Soil Science
and Agricultural Chemistry and the laboratory attached to the All India Network Project
(AINP) on Pesticide Residues, College of Agriculture, Vellayani, Thiruvananthapuram,
Kerala during 2019-21. The main objectives of the experiment were to study the
adsorption, desorption, persistence and leaching of cyantraniliprole in sandy loam soils
with and without addition of organic amendment at the rate of 0.5 per cent Farm Yard
Manure (FYM).
The
soil
was
collected
from
the
sandy
belts
of
Kazhakkoottam,
Thiruvananthapuram. The physical and chemical analysis of the soil revealed that the soil
was moderately acidic, with 0.84 per cent organic matter, 11.80 per cent clay, 22.30 per
cent silt and 65.90 per cent sand. Among the major nutrients, phosphorus content was found
to be high; potassium was medium while the other nutrients were low. The method for
estimation of cyantraniliprole residues in soil were validated by modified QuEChERS
method and was found ideal. Liquid- liquid partitioning using dichloromethane was found
suitable for cyantraniliprole residue estimation in water.
The adsorption-desorption studies were carried out at 5 different concentrations of
20, 40, 60, 80 and 100 μg levels each both in normal soil and 0.5 per cent FYM amended
soil in Completely Randomized Design (CRD) with ten treatments and three replications
and was repeated by direct spiking also. The adsorption- desorption data fitted well in
Freundlich adsorption isotherm. The distribution coefficient, K d (mean value) was found
high in amended soil (2.55) than normal soil (2.40) which indicated increased sorption in
relation to organic matter content. The K f values (adsorption coefficient) were 2.60 and
2.45 for amended and normal soil respectively, indicating a high sorption capacity for the
amended soil. The desorption was carried out in three cycles, the percentage desorption
was decreasing in each consecutive cycle. In all levels of concentration, desorption was
slower than adsorption indicating a hysteresis effect. In the soil samples directly spikedwith cyantraniliprole also, the desorption percentages were found lower and formed a still
higher hysteresis.
Mobility of cyantraniliprole was assessed in CRD with eighteen treatments and
three replications i.e., by loading 3 levels viz., 25, 50 and 75 μg concentrations of
cyantraniliprole, separately on top of 200 g soil columns loaded in PVC pipes and followed
by eluting with 40, 80 and 160 mL of water @ 0.4 ml min -1 . In all the treatments residues
were obtained in 0-25 cm packed columns and also in the leachate. In the normal soil,
cyantraniliprole moved down the soil column which resulted in residue levels ranging from
7.48-3.98, 19.27- 9.57 and 27.67- 13.41 μg at 25, 50 and 75 μg levels, respectively when
eluted with different volumes of water. In the soil amended with 0.5 per cent FYM, the
corresponding residues ranged from 10.41- 4.48, 21.08- 9.89 and 29.98- 14.19 μg at 25, 50
and 75 μg levels indicating a higher retention in soil.
The persistence of cyantraniliprole in normal soil and amended soil under three soil
moisture conditions (air dry, field capacity and saturated) were studied using the
formulation of cyantraniliprole added at the rate of 1, 2 and 4 mg kg -1 in CRD with eighteen
treatments and three replications. The half- life of cyantraniliprole was found highest in
amended soil spiked with 4 mg kg -1 cyantraniliprole under air dry soil condition i.e., 32.44
days followed by the same under normal soil condition i.e., 30.45 days. In the persistence
study, no metabolites of cyantraniliprole were detected.
The study concluded that the adsorption coefficient was higher in FYM amended
soil indicating stronger adsorption than normal soil and the desorption percentages were
reduced in the same. Hysteresis effect was noticed in all the treatments indicating slower
desorption than adsorption. The mobility of cyantraniliprole was found to be slightly higher
in normal soil compared to the 0.5 per cent FYM amended soil and also indicates its
moderate mobility behaviour. The dissipation was found to be the fastest under submerged
condition followed by field capacity and air dry conditions.