Abstract
A series of experiments were carried out at Bangladesh
Agricultural University, Mymensingh to study the growth pattern,
production and postharvest behaviour of sweet potato cv. Tripti
during the period from 1992 to 1994.
Sweet potato plants followed a sigmoid type of growth curve
with 3 distinct phases of growth. First phase (within 45-60 days
after planting) was marked by profuse development of fibrous
roots and initiation of tuberous roots, while the second phase
(45-60 days up to 105 days) was characterized by the highest rate
of shoot growth and maximum number of leaf production. The third
phase (105 dap onward) on the other hand showed yellowing and
senescence of older leaves, decrease in leaf area index (LAI) and
maximum bulking of tuberous roots. Maximum LAI (9.1) was noticed
at 105 dap. Net assimilation rate (NAR) was higher during initial
plant establishment, at 105 and 135 dap. Total crop growth rate
(CGR) exhibited two peaks at 105 and 135 dap which coincided with
the maximum growth rate of shoot and roots respectively. Relative
growth rate (RGR) was highest during initial stage and declined
continuously with increase in bio-mass production. A positive
correlation was noticed between LAI and CGR, and NAR and CGR, but
not between LAI and NAR.
Application of plant growth regulators such as NAA (10, 20,
30, ppm), сусосel (1000, 2000, 3000, ppm), ethrel (100, 250, 400,
ppm), maleic hydrazide i.e. MH (100, 250, 400, ppm) at 30 and 60
dap had less effect on the production of sweet potatoes. Ethrel
and MH treated plants produced slightly smaller leaves, but MH
treated leaves were narrow and distorted. Average size of the
tubers was slightly increased by ethrel treatment. Application
of 10000 ppm cycocel and 1000 ppm ethrel at 30 and 60 dap
respectively was found effective to increase both number and yield of the tubers. Treatments of plant by paclobutrazol (10,
100 and 1000 ppm) produced increased size and yield of the
tubers, but showed compact and reduced shoot. The effect was more
pronounced at higher concentration. None of these plant growth
regulators applied during growing period in either experiments
affected the postharvest behaviour. On the other hand,
postharvest treatment of tubers in NAA, сусосel, ethrel and МH
at 1000, 2000 and 3000 ppm solution revealed that only NAA was
effective to inhibit or delay sprouting. MH treated tubers
produced more number of distorted sprouts. Ethrel enhanced the
rotting and sprouting. Cycocel had no effect at all.
When five levels of nitrogen (0, 60, 80, 100 and 120 kg
N/ha) and potash (0, 100, 120, 140 and 160 kg K₂O/ha) were
applied with or without cowdung (10 t/ha) and Dhaincha green
manuring, it was evident that application of both nitrogen and
potash increased the yield, but the variations among different
levels were not significant. Tuber number was slightly reduced
by heavy application of nitrogen. Dry matter content of the tuber
was increased by nitrogen and decreased by the application of
potash. The number of sprouts during storage were significantly
affected by both nitrogen and potash. The number was found to
increase gradually with the increasing dose of nitrogen, while
reverse trend was noticed with potash. The effect of these
fertilizers was more pronounced when sweet potatoes were grown
without green manuring and cowdung application.
Experiments with different stages of maturity (3, 4, 5 and
6 months) and storage conditions (light and dark) suggested
economic yield by harvesting the crop at 5 months after planting.
Weight loss during storage was higher in immature tubers compared
to matured ones, however tubers from 6 months crop showed
comparatively higher weight loss than those from 5 months crop.
Irrespective of the maturity stage, weight loss and sprouting
were delayed in dark stored sweet potatoes. In ordinary light
storage greening was the serious problem. The intensity of the greenness was higher in immature tubers. On the other hand,
matured tubers were more prone to weevil infestation.
Removal of the vine before few days (4 and 8) of harvest
increased the dry matter content and free sugar of the tubers.
Conversely, a loss of starch on dry weight basis was noticed.
Tubers from these treatments sprouted earlier during storage and
thus could not be stored for longer period.
Various methods of aboveground, semi-underground and
underground storage were utilized to store sweet potatoes. Among
different aboveground storage methods storage of sweet potatoes
in dry sand was found to be the best exhibiting reduced rate of
weight loss, lesser change in dry matter and starch and no weevil
infestation. Curing before storagë reduced the rate of weight
loss and rotting during storage. Provision of ventilator had no
benefit in cured sweet potatoes. Sweet potatoes in underground
and semi-underground storage showed reduced rate of.weight loss
and lesser change in dry matter, starch and sugar.
Weevil infestation was found to be delayed but not
controlled when the leaves of Neem (Azadirachta indica), Pitraj
(Amoora rohituka), Nishinda (Vitex negundo L.), Bishkatali
(Polygonum longifolia), Bael (Aegle marmelos), Debdaru
(Polyalthia longifolia) and Lantana (Lantana camera) were used in
storage.