MSc

An investigation was carried out at College of Agriculture. Vellayani, to
study the feasibility of using phosphogypsum as an ameliorant for correcting soil
acidity in laterite soil with cowpea as the test crop. The experiment comprises of
an incubation study and a micro plot field experiment.
The incubat{on study was carried out to understand the kinetics of
dissolution of phosphogypsum and the nutrient release pattern in laterite soils
after its application with the following seven treatments T I (absolute control) T2
(Lime @ full LR), T3 (PG @ full LR) T4 (Lime @ half LR), r, (PG @ half LR)
T6 (Lime and PG each @ half LR) T7 (Lime as per POP). The study was
conducted for a period of 60 days and the chemical parameters were analysed at
an interval of 12 days as per standard procedures.
The results revealed the enhanced solubility of phosphogypsum which was
evident from the higher EC values in the treatments with phosphogypsum through
out the study period. Most of the plant available nutrients were solubilised by the
24 th day of incubation.
A reduction in exchangeable acidity was noticed by the application of
phosphogypsum after a peri,od of 24 days, which is mainly due to reduction in
exchangeable aluminium. But this was not efficient as lime in decreasing the
exchangeable H+ and hence the pH, remained unaltered.
The micro plot field experiment was laid in RBD with a main crop and a
residue crop of cowpea var. Kanakamoni. The treatments include TI (POP), T2
(Lime @ full LR), T 3 (PG @ full LR), T 4 (Lime @ half LR), T s (PG @ half LR),
T 6 (Lime and PG each @ half LR), T 7 (Lime and PG each @ 14 LR) and T 8
(absolute control). Fertilizers and amendments were applied on the basis of soil
test data except in T I where, they were applied on the basis of POP of Kerala
Agricultural University. In the residue crop, the amendments were not added and
was taken immediately after the main crop.

The available nutrients in soil like, P, Ca and S were increased by the
application of phosphogypsum. However, considerable leaching was noticed in
the case of Mg and K.
The growth characteristics of cowpea were improved by the application of
phosphogypsum. The highest grain yield was recorded with phosphogypsum
applied at full LR and was on par with the combination treatment which received
the amendments at one fourth LR. But considering the cost factor treatment with
phosphogypsum at full LR is the best. Its B: C ratio was also the highest among
other treatments. The yield attributes were also improved by the treatment with
phosphogypsum at full LR.
The concentration and uptake of N, P, K, Ca, and S in bhusa were
favourably influenced by the application of phosphogypsum either at full LR or at
halfLR.
The residual effect of phosphogypsum was visualized in the crop, taken
after the main crop. The application of phosphogypsum increased the organic
carbon content, P, and S. The leaching of calcium, Mg and K beyond the root
zone was much pronounced in the residue crop.
The yield attributes of cowpea were also positively related with
phosphogypsum treatment. But by the time of residue crop, the bhusa yield was
more for lime treated plots'.
The concentration of N, Ca and Mg were more in lime treated plots, but
the uptake of nutrients was more for treatment with phosphogypsum. This also
emphasizes the mobility and downward leaching property of phosphogypsum.
The micronutrient content and uptake were also influenced by the application of
phosphogypsum.
Phosphogypsum is hence highly beneficial in increasing the yield and
yield attributes of cowpea, by mitigating the adverse effects of soil acidity, such
as aluminium toxicity, which in effect is the major reason for acidity in laterite
soils. Further, utilization of an industrial by product, which otherwise remain
unutilized is also facilitated.