Ph D

The study entitled “Organic nutrition in taro (Colocasia esculenta (L.) Schott)”
was conducted at College of Agriculture, Vellayani, Thiruvananthapuram, Kerala to
investigate the effect of organic nutrition on growth, yield, quality, soil organic carbon
build up and economics of cultivation of taro and to study rooting and tuberisation pattern
of taro under organic nutrition. The experiment was conducted in the farmer’s field at
Peringamala, Thiruvananthapuram from June 2019 to January 2020 and June 2020 to
January 2021.
The investigation comprised two separate experiments: (1) Organic nutrition in
taro (field experiment) and (2) Rooting and tuberisation pattern study in taro (pot
culture). The first experiment was laid out in randomized block design with three
replications. The treatments comprised six organic sources (s1- FYM + wood ash; s2-
FYM + wood ash +PGPR mix I; s3- FYM + wood ash + PGPR mix I + vermiwash; s4-
poultry manure + wood ash ; s5- poultry manure + wood ash + PGPR mix I; s6- poultry
manure + wood ash + PGPR mix I + vermiwash) and two in situ green manuring (g1- in
situ green manuring with cowpea; g2- in situ green manuring with daincha) with three
controls (C1- nutrient management through chemical fertilizers as per KAU POP (80 :
25: 100 kg ha-1
); C2 - nutrient management as per KAU organic POP (Ad hoc); C3 -
absolute control). The tuberization study was laid out as completely randomized design
as pot culture with the six organic sources (s1 to s6 used in field experiment) as treatments
(T1 to T6) together with three controls, and were replicated thrice. The recommended
dose of NPK for colocasia @ 80: 25: 100 kg ha-1 was applied through organic sources on
N equivalent basis as per the treatments.
Application of FYM + wood ash +PGPR mix I (s2) took less number of days
(24.33 days) for 50 per cent sprouting of seed corm during first year. Application of
poultry manure along with wood ash, PGPR mix I and vermiwash (s6) and in situ green
manuring with daincha (g2) found superior with respect to growth characters such as
plant height, number of leaves per plant, leaf area and leaf area index (LAI). The
interaction s6g2 recorded taller plants, higher leaf area and LAI during both the years.
Taller plants were produced by s6g2 at 4 MAP and s6g1 at harvest compared to C1 (151.48
cm) during first year. Organic treatments performed better than C2 and C3 with respect to
all growth parameters.
FYM + wood ash and poultry manure + wood ash recorded the highest number of
cormels per plant during first and second year respectively. Mean weight of cormel was
higher in s6 (34.86 g) during first year and in s3 (26.01 g) during second year. The
application of poultry manure along with wood ash, PGPR mix I and vermiwash (s6)
recorded the highest cormel yield (18.68 t ha-1
) and corm yield (12.21 t ha-1
) under
pooled analysis. Organic treatment s5 recorded the highest cormel to corm ratio (1.80)
during second year. In situ green manuring with daincha (g2) recorded the highest mean
cormel weight during both the years while cormel and corm yield in pooled analysis were
also the highest with this treatment. The treatment s3g2 recorded the highest mean weight
of cormel and the treatment s6g2 recorded the highest cormel yield under pooled analysis
(19.02 t ha-1
). The treatment s5g1 registered the highest cormel to corm ratio during
second year. The organic treatments s3g2, s5g1, s5g2, s6g1 and s6g2 were found to be equally
effective as C1 in case of corm and cormel yield of taro. The treatment s6g2 recorded a
0.90 percentage increase of cormel yield over chemical nutrient management during first
year and a 2.67 percentage increase of corm yield over chemical nutrient management for
pooled mean. The treatment combinations s3g2, s5g1, s5g2, s6g1 and s6g2 were found
superior to C2 in case of corm yield, cormel yield and mean cormel weight. The
treatment s6g2 recorded a 37.83 percentage and 27.82 percentage increase of cormel yield
and corm yield respectively over KAU organic POP for pooled mean. The treatments
s3g2, s4g2, s6g1 and s6g2 during first year and s3g2, s5g2 and s6g2 during second year
recorded significantly higher mean weight of cormel than C3. All the treatment
combinations in case of corm yield and all the treatment combinations except s1g1 in case
of cormel yield recorded significantly higher value than C3. During second year, the
treatments s5g1 and s2g2 recorded the highest harvest index (0.60) and were significantly
superior to C2 (0.47).
The organic source s6 and in situ green manuring g2 recorded the highest dry
matter production (DMP). Treatment combination s6g2 (8.37 t ha-1
) during first year and
s3g2 (6.55 t ha-1
) during second year recorded the highest DMP. Except s1g1, s1g2 and s4g2,
all other treatment combinations resulted in significantly higher DMP compared to C2.
All organic treatments were significantly superior to C3 with respect to DMP during both
the years. The organic source s6 and in situ green manuring g2 were found superior in
improving quality characters of cormel.
The higher N and K content and uptake were noticed in organic source s6, while P
uptake was higher in s3. In situ green manuring g2 resulted in higher NPK contents and
uptake. The highest N (149.03 kg ha-1
) and K (232.80 kg ha-1
) uptakes were recorded
with treatment combination s6g2 during second year. During first year, the treatment s3g2
recorded the highest tuber P content and P uptake (35.12 kg ha-1
). The treatment
combination s6g2 was significantly superior to C1 in case of K uptake during first year.
The treatment combinations s2g1, s2g2, s3g1, s3g2, s5g1, s5g2, s6g1 and s6g2 were found
superior to C2 in nutrient content and uptake. The organic treatments were superior to
absolute control in nutrient contents and uptake.
The organic source s5 recorded the lowest EC during second year. The organic
sources s5 and s6 resulted in higher organic carbon and available N content in soil while
available P content of soil was the highest with s3. In situ green manuring with daincha
found superior in organic carbon, available N and available P content of soil. Available N
content in soil was the highest in s6g2 during first year. The treatments s2g2 and s3g2 were
found to be significantly superior to C1 and C2 during second year with respect to
available P status. The organic treatments were found superior to C3 in case of pH,
organic carbon and available NPK. The organic sources s5, s3, s6 and in situ green
manuring g2 resulted in higher total organic carbon and recalcitrant carbon, labile carbon
and water soluble carbon content of soil. All organic nutrition treatments were found
superior to control treatments in soil organic carbon buildup. Balance sheet of K was
positive for s3g1, s5g1, s6g1, s6g2 and C1 after first year of experiment and the N balance
was positive for absolute control after second year.
The organic source s6 and in situ green manuring g2 registered the highest net
income and BCR. Treatment combination s6g2 resulted in the highest net income
(₹737241 ha-1
) and BCR (2.82). All the treatments except s1g1 and s2g1 recorded higher
net income and the treatments s4g1, s5g1, s6g1 and s6g2 resulted in higher BCR than C1. The
treatment s6g2 recorded a 43.96 percentage and 6.02 percentage increase of net income
and BCR respectively over chemical nutrient management for mean. All treatment
combinations except s1g1 and s2g1 recorded higher net income and all except s1g1, s2g1
and s3g1 recorded higher BCR compared to C2. The treatment s6g2 recorded a 54.71
percentage and 19.49 percentage increase of net income and BCR respectively over KAU
organic POP for mean. All organic nutrition treatments recorded higher net income and
all treatments except s2g1 and s3g1 recorded higher BCR compared to absolute control.
In pot culture study, the treatments T6 and T5 in case of pH, absolute control in
case of EC, T2 and T3 in case of organic carbon and available P and T6 and C1 in case of
available N and K were found superior throughout the growing period. The higher
microbial population was observed with organic sources T6, T5, T3 and T2. The organic
sources T5 and T3 recorded the highest dehydrogenase activity. The treatments T6, T3 and
T5 excelled in rooting pattern and root anatomical characters. Significant and positive
correlation was observed between nutrient uptake and root apex diameter, late metaxylem
number, early metaxylem number and stele diameter. Corm initiation was early (between
1 MAP and 2 MAP) in treatments C1 and T6 while it was between 2 MAP and 3 MAP in
all other treatments. Control C1 and T6 recorded the highest corm and cormel weight per
plant during initial stages and later stages respectively. The highest values of cormel
bulking rate were observed between 3 MAP and 4 MAP. The treatment T6 recorded the
highest bulking rate during 3-4 MAP, T3 and T5 during 4-5 MAP and T2 during 5-6 MAP.
The study revealed that application of poultry manure, wood ash, PGPR mix I and
vermiwash, along with in situ green manuring of daincha in taro resulted in higher
growth, yield, quality, net returns and BCR under organic nutrition and hence can be
recommended for its organic nutrient management. All the organic nutrient management
practices were found to improve soil organic carbon build up. Application of poultry
manure, wood ash, PGPR mix I and vermiwash as organic sources was also found to
promote the rooting and tuberisation in taro.