PhD

Three field experiments were conducted in the wet lands and garden
lands of Instructional farm of College of Agriculture, Vellayani to work
out cultural, manurial and water requirements for sweet potato. The
treatments in the first experiment – Nutritional requirements of sweet
potato – consisted of three level of nitrogen (50, 70 and 100kg N/ha), three
levels of phosphorus (25, 50 and 75kg P2O5/ha) and three levels of
potassium (50, 75 and 100kg K2O/ha). The experiment was laid out in a 33
partially confounded factorial design with two replications. The second
experiment – spacing cum depth of application of fertilizers – consisted of
three spacing (40cm x 20cm, 60cm x 20cm and 80cm x 20cm) and three
depths of application of fertilizers (10cm, 20cm and 30cm).
The
experiment was laid out in a 32 factorial design in RBD with four
replications. The third experiment – Irrigation requirement – consisted
of four levels of irrigation (IW/CPE ratios 0.25, 0.50, 0.75 and 1.00) and
four levels of fertilizers (50:25:50, 75:50:75, 100:75:100 and 125:100:125
kg N,P and k/ha). The experiment was laid out in a split plot design with
five replications.
In the experiment to study the nutritional requirement of sweet potato
growth attributes like length of vine, number of branches and leaf area
index were maximum at higher
levels of nitrogen and potassium. The highest values of tuber number,
tuber weight, length of tuber and girth of tuber were obtained by the
application of 75kg N, 50kg P2O5 and 100kg K2O/ha. Application of
nitrogen, phosphorus and potassium at the rate of 75:50:100 kg/ha was
found to be optimum for higher tuber yield. While nitrogen nutrition
increased the protein content of tuber, potassium application enhanced
the starch content. Highest levels of nitrogen, phosphorus and potassium
increased the leaf, stem and tuber dry matter production and tuber
bulking rate.
Potassium only did influence the net assimilation rate.
Crop growth rate was maximum at higher levels of nitrogen, phosphorus
and potassium.
The plant uptake of nitrogen, phosphorus and potassium was maximum
at the highest level of these nutrients. The NPK combination of 75kg N,
50kg P2O5 and 100kg K2O/ha resulted in the maximum net return.
Experiment on spacing cum depth of application of fertilizers revealed
that wider spacing of 80cm x 20cm enhanced the growth characters such
as length of vine, number of branches and LAI. Depth of application was
not influential on this aspect. Yield attributes like tuber number, tuber
weight and girth of tuber were higher at the spacing of 40cm x 20cm but
length of tuber was maximum under wider spacing.
Application of
fertilizers at 20cm depth recorded maximum values for the aforesaid
characters.
Closer spacing of 40cm x 20cm and 20cm deep placement of fertilizers
recorded higher tuber yield.
Among the quality attributes protein
content alone was influenced by wiser spacing, but protein and starch
contents were increased when fertilizers were applied at 20cm depth.
Wider spacing increased leaf and stem dry matter and CGR while closer
spacing recorded higher tuber dry matter, tuber bulking rate and net
assimilation rate. Depth of application of fertilizers did not influence the
dry matter production.
Plant uptake of nitrogen, phosphorus and
potassium was increased by wider spacing and by the application of
fertilizers at a depth of 20cm. A combination of 40cm x 20cm spacing
and 20cm deep fertilizer placement resulted in maximum net return.
Experiment on irrigation requirements divulged that highest IW/CPE
ratio and higher fertilizer combinations recorded maximum length of
vine and LAI, but number of branches was not influenced by them.
Number of tubers, weight of tubers, length of tubers and girth of tubers
were not influenced by irrigation, while levels of fertilizers increased the
length of tubers.
Tuber yield was higher at IW/CPE ratio of 0.75.
Fertilizer combination of 100:75:100 kg of N, P and k/ha produced the
maximum yield. Starch and protein contents were increased at higher
levels of irrigation and fertilizer application. Total dry matter
production and bulking rate increased upto an IW/CPE ratio of 0.75 and
upto a fertilizer lever of 100:75:100 kg N, P and k/ha. Plant uptake of
nitrogen, phosphorus and potassium at harvest was maximum at higher
levels of irrigation and fertilizer application. Irrigating the field when the
IW/CPE ratio becomes 0.75 and application of fertilizers at a ratio of
100:75:100 kg N, P and k/ha recorded maximum net returns.