MSc

An investigation entitled "Verrnicompost as a potential organic source
and partial substitute for inorganic fertilizers in sweet potato (Ipomoea batatus
(L) Lam)" was carried out at the Instructional Farm, College of Agriculture,
Vellayani during the period December 1995 to April 1996. The main
objectives of the study were to study the efficiency of vermicompost as an
organic manure, the extent to which inorganic fertilizers can be substituted
when vermicompost was used as an organic source and the feasibility of



reducing the dose of vermicompost.


The experiment was laid out III



randomised block design with seven treatments and four replications. The
treatments consists of package of practices recommendations of Kerala
Agricultural University for sweet potato (cattle manure + inorganic fertilizers)
and vermicompost as organic source with graded doses of inorganic fertilizers.
The growth parameters like vine length and number of branches did not
show any significant variation. However highest vine length and number of
branches are noticed in treatment which received vermicompost as a sole
source of nutrient. Significant difference was observed in vine yield and
highest vine yield was obtained when vermicompost was given as a sole source
of nutrients. Yield attributing characters like length and girth of tubers and
number of tubers did not show any significant variation. With respect to mean
tuber weight and tuber bulking rate, the treatment differed significantly and
maximum effect was observed when vermicompost was applied along with half
the recommended dose of inorganic fertilizers.

Significant treatment effect could be observed in total tuber yield and
marketable tuber yield. Vermicornpost with half or 3/4th NPK produced
highest yield. From this it could be deduced that by using vermicompost as
organic manure in sweet potato, it is possible to bring down the usage of
chemical fertilizers. Half or 3/4th dose of vermicompost along with
recommended dose of inorganic fertilizers was equally effective as that of
package of practices recommendations of Kerala Agricultural University (cattle
manure + recommended inorganic fertilizers) in yield and yield attributes of
sweet potato.
The nitrogen and phosphorus content in the leaves and vmes did not
show any significant difference by applying various treatments. But in tubers
the nitrogen content was maximum when 1/2 inorganic fertilizers + organic
manure as vermicompost was applied. The phosphorus accumulation in tuber
was maximum in the combination of full inorganic fertilizers + organic manure
as cattle manure was given. The treatment combination of full inorganic
fertilizers + organic manure as vermicompost resulted m maximum
accumulation of phosphorus in leaves, vines and tubers. Regarding calcium,
magnesium and iron contents of leaves, vines and tubers there was no
significant difference among various treatments. The application of full
inorganic fertilizers + organic manure as vermicompost produced maximum
manganese concentration in leaf and tuber.
The starch content of tubers showed a decreasing trend with the
reduction in the quantity of inorganic fertilizers. But by reducing inorganic
fertilizer levels, the reducing sugar percentage increased. The crude protein,

crude fibre and carotene contents showed the same trend as that of reducing
sugar.
The plant uptake of nitrogen, phosphorus and potassium was maximum
when 112 inorganic fertilizers + organic manure as vermicompost was applied.
The organic carbon level after the crop showed significant difference among
various treatments. The maximum organic carbon percentage was noticed
when nitrogen as vermicompost + organic manure as vermicompost was given.
The growth characters like vine yield, number of branches were
negatively correlated with yield. The yield components like number of tubers
per plant, tuber weight, uptake of nitrogen, phosphorus and potassium showed
positive correlations with yield.
The economics worked out show that the highest net profit was
obtained when 1/2 inorganic fertilizers + organic manure as vermicompost was
given. The cost of cultivation while applying this treatment was minimum and
it showed a B C ratio of 2.53.