PhD

The investigation entitled “Fertigation studies in papaya (Carica papaya L.)”
was carried out in Instructional Farm, College of Agriculture, Vellayani during the
period 2018 – 2020 with the objectives to standardize the nutrient level for yield
improvement through fertigation and foliar nutrition in papaya variety Surya and to
study the postharvest management practices for extending the shelf life of papaya
fruits.
The experiment was undertaken in two parts. In part I, standardization of
nutrient level for fertigation and foliar nutrition was carried out in RBD with 14
treatments replicated thrice. A combination of four fertigation doses of 75 %, 100 %,
125 % and 150 % RDF of N (304.89, 406.52, 508.15 and 609.78 g urea plant⁻¹ year⁻¹
respectively based on soil test data in 76 fertigation) and K (426.25, 568.33, 710.42
and 852.50 g MOP plant⁻¹ year⁻¹ respectively based on soil test data in 76 fertigation)
and three foliar sprays (1.0 % 19:19:19 at bimonthly interval starting from 4 MAP to
16 MAP, 0.5% ZnSO4 + 0.3% borax at 4
th, 8th, 12th and 16th MAP and water spray at
bimonthly interval starting from 4 MAP to 16 MAP) were compared with soil
application of recommended dose of NPK (187:170:341 g NPK plant-1
year-1
based
on soil test data) (control 1) and 187:170:341 g NPK plant-1
year-1
based on soil test
data as organic manures as combination of FYM, poultry manure and vermicompost
in the ratio of 2:1:1 (control 2). In control 2, additional requirement of P and K were
met through the application of rock phosphate and potassium sulphate respectively.
Organic manure (15 kg FYM plant-1
) was given uniformly to all treatments as basal.
Lime and rock phosphate (500g and 850g respectively based on soil test data) was
applied uniformly for all treatments as basal except controls. Urea and Muriate of
Potash (MOP) were used as fertilizer sources for fertigation and applied weekly from
1 MAP to 20 MAP.
Application of different levels of fertigation and different foliar sprays had
significant effect on growth, yield and quality of papaya. Growth parameters viz.,
plant height, stem girth and number of leaves were significantly higher in plants
receiving 100 % RD of N and K through fertigation and foliar sprays of 1.0 %
19:19:19 (T4) at bimonthly interval starting from 6 MAP to 16 MAP. T4 also recorded
highest leaf area index at 6, 12, 18 MAP and at final harvest, flowering at the shortest
height, highest number of female plants and highest fruit set (86.27 %). However,
application of 100 % RD of N and K through fertigation and foliar sprays of 0.5 %
ZnSO4 and 0.3 % borax at 4
th, 8th, 12th and 16th MAP (T5) initiated earliness in
flowering (142.67 days) and harvest (275.00 days).
Treatments T4 and T5 were on par in fruit length, fruit girth, fruit volume, pulp
percentage, flesh thickness and yield contributing characters like fruit weight, number
of fruits per plant and yield per plant (38.30 kg plant⁻1
and 37.60 kg plant⁻1
respectively). Fruit quality parameters viz., TSS, carotenoids, ascorbic acid, total
sugar, reducing sugar and non reducing sugar were found highest in T5. Fruits from
T5 also registered longest shelf life (5.78 days) and highest mean sensory score for all
parameters. Index leaf analysis at 6 MAP revealed highest nitrogen and potassium
content of leaf in T10 (150 % RD of N and K through fertigation and foliar sprays of
1.0 % 19:19:19). Calcium, magnesium and sulphur content of leaves were highest in
T5, whereas boron and zinc content were highest in T8 (125 % RD of N and K
through fertigation and foliar sprays of 0.5 % ZnSO4 and 0.3 % borax). Highest
nitrogen and potassium of fruits were observed in T12 (150 % RD of N and K through
fertigation with water spray). Highest nitrogen content in soil was noticed in T11 (150
% RD of N and K through fertigation and foliar sprays of 0.5 % ZnSO4 and 0.3 %
borax) and T10 witnessed highest potassium content. T4 and T5 were at par regarding
B : C ratio (2.58 and 2.54 respectively).
In part II of the investigation, postharvest management for extending shelf life
of papaya was carried out with nine treatments replicated thrice. Different postharvest
treatments given were precooling - hydro cooling (S1), surface sanitization with 150
ppm sodium hypochlorite (S2), external coating with 1% chitosan (S3), precooling
followed by external coating with 1% chitosan (S4), packaging with ethylene scrubber
8% KMnO₄ (S5), precooling followed by packaging with ethylene scrubber 8%
KMnO₄ (S6), precooling followed by external coating with 1% chitosan and
packaging with ethylene scrubber 8% KMnO4 (S₇), hot water treatment followed by
waxing with 6% carnauba wax and packaging with ethylene scrubber 8% KMnO₄
(S8) and control (S9). Papaya variety Surya was raised at Instructional Farm,
Vellayani and fruits at fully mature green stage were harvested, subjected to different
postharvest treatments and packaging was done in CFB boxes and stored under
ambient conditions till the end of shelf life.
Papaya fruits subjected to precooling followed by external coating with 1%
chitosan and packaging with ethylene scrubber KMnO₄ (S7) recorded the longest
shelf life of 9.67 days, which was at par with S8 (hot water treatment followed by
waxing with 6% carnauba wax and packaging with ethylene scrubber KMnO₄).
Physiological loss in weight, ion leakage, percentage disease index, bacterial and
fungal count were significantly lowest in S7 and S8 after three days of storage. These
treatments also recorded maximum total carotenoids, total soluble solids, total sugar,
reducing sugar and minimum acidity after nine days of storage which indicated
extended shelf life. Highest mean rank score for sensory attributes were also recorded
in treatments S7 and S8 after nine days of storage.
In conclusion, application of 100 % recommended dose of N and K (406.52 g
urea plant⁻¹ year⁻¹ and 568.33 g plant⁻¹ year⁻¹ respectively) through weekly
fertigation from one to 20 months after planting and foliar sprays of 0.5 % ZnSO4 +
0.3 % Borax at 4
th, 8th, 12th and 16th MAP, along with basal application of 850g rock
phosphate and 15 kg FYM resulted in increased growth, yield and quality characters
of papaya variety Surya with highest B: C ratio. Fruits at fully mature green stage
when subjected to precooling followed by external coating with 1% chitosan and
packaging with ethylene scrubber 8% KMnO₄ in CFB boxes exhibited a shelf life of
9.67 days in storage under ambient condition in papaya variety Surya.