MSc

Rock phosphate sources collected from different locations were analysed
for both phosphorus content and heavy metals namely cadmium and lead. Those
sources which analysed relatively higher content of heavy metals were included for
conducting a pot culture experiment using chilli (Capsicum annuum L.) as test
crop. To derive meaningful comparison in the study, partially acidulated rock
phosphates as well as direct water soluble source of cadmium and lead were also
applied to assess their bioavailability to plants. The influence of organic matter
when applied alone or in conjunction with heavy doses of heavy metals was also
assessed in the study.
The pot culture experiment was conducted in the Vegetable Research
Farm, Department of Olericulture, Vellanikkara during the kharif season of 1996,
with chilli as the test crop. The entire fertilizer management was based on package
of practice (N, P and K at 70, 40 and 25 kg ha-1) recommendation. Five different
sources of P selected for the pot culture experiment were (1) Maton rock phosphate,
(2) Mussorie rock phosphate, (3) Gafsa rock phosphate, (4) Rajasthan rock
phosphate and (5) Single superphosphate.
The maximum content of cadmium (55 mg kg-1) was recorded in Gafsa
rock followed by 25 mg Cd kg-1 for the Maton rock and single superphosphate
analysed the least concentration of cadmium (15 mg kg-1 Highest lead content of
230.5 mg Pb kg-1 was analysed in Maton rock while lowest (38 mg kg-1) in
Musoorie rock. All the other sources maintained their heavy metal concentration in
between these extremes.


In general, the shoot portion of test crop chilli recorded highest cadmium
uptake while root portion noted the maximum lead uptake. The least uptake of
heavy metals was noted in the chilli fruit, which is the edible part of the plant. This
indicates that the heavy metal load in the fruit portion is much less when compared
to other plant parts, irrespective of the sources used. The same trend was evident
when either partially acidulated P sources or direct source of heavy metals (through
water soluble salts) were applied. However, the uptake of cadmium and lead from
those sources remained higher in plant parts.
Application of organic matter in conjunction with a heavy dose of heavy
metals to soil resulted in a significantly higher uptake of cadmium and lead in all
plant parts.
Analysis of the available cadmium and lead in the post-harvest soil
samples indicated negligible build-up of these metals in soils. However, direct
application of higher levels of heavy metals permitted higher cadmium and lead
extraction in the post-harvest soil samples. Application of partially acidulated rock
sources to soils, though could cause enhanced uptake of heavy metals, could not
show higher residual effects of heavy metals in post-harvest soil samples.