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The research work entitled ‘Resource management for source-sink
modulation in Chinese potato [Plectranthus rotundifolius (Poir.) Spreng.]’ was
undertaken at College of Agriculture, Vellayani during 2018 – 2021. The main
objectives were to study the influence of planting methods, nutrient management
practices and growth promoters on source-sink relationship, tuber yield and
quality in Chinese potato, to assess the growth and yield responses of the crop to
carbon dioxide (CO2) fertilization and to work out the economics.
The investigation was carried out as two experiments: i) influence of
planting methods, nutrient management practices and growth promoters on source
- sink relationship, tuber yield and quality and ii) influence of CO2 fertilization on
growth and yield responses in Chinese potato. The photo insensitive variety
Suphala, released by Kerala Agricultural University (KAU), was used for the
study. Experiment I was conducted during October 2019- February 2020 and
repeated during 2020-2021 for confirmation. It was laid out in split plot design
with five methods of planting as main plots and six combinations of two nutrient
management practices and three growth promoters as sub plot treatments, in four
replications. The methods of planting included were m1: bed method (30 cm x 15
cm), m2: bed method (30 cm x 30 cm), m3: ridge method (30 cm x 15 cm), m4:
ridge method (30 cm x 30 cm) and m5: mound method (30 cm x 30 cm). The
combinations comprised nutrient management practices (n1: 60:30:120 kg NPK
ha-1 + PGPR Mix 1, n2: 60:30:120 kg NPK ha-1) and growth promoters (g1: humic
acid @ 5 g L-1, g2: benzyl adenine @ 50 mg L-1 and g3: water spray). PGPR Mix 1
(2 %) was applied @ 5 g per plant, thrice, at the time of planting, 30 DAP and 60
DAP in n1 and growth promoters were sprayed 45 and 75 DAP. Other cultural
operations were done as per package of practices of KAU.
Bed method of planting at 30 cm x 15 cm (m1) produced significantly
taller plants with higher leaf area index (LAI), dry matter production (DMP) and
crop growth rate (CGR) in both the years. Planting at the wider spacing (30 cm x
30 cm) on beds (m2) or ridges (m4) resulted in higher and comparable values for
number of branches and plant spread (N-S and E-W), while m2 showed superiority
in the number of leaves and leaf area per plant at 45 and 90 DAP. The wider
spacing, irrespective of the method of planting, revealed markedly higher relative
growth rate (RGR) during 45-90 DAP and the trend remained similar in both
years. Significantly higher net assimilation rate (NAR) between 45-90 and 90-135
DAP, and chlorophyll content were noted in m2. Higher chlorophyll content in m2
was on par with m4 during second year.
Per plant tuber attributes (number of tubers, tuber yield, marketable tuber
yield and average tuber weight) were found superior in bed planting at 30 cm x 30
cm. But, average tuber weight was comparable with m4 in the first year and with
m4 and m5 in the second year. Per hectare tuber yields were significantly the
highest in the bed method of planting at 30 cm x 15 cm spacing, during both the
years with a pooled mean of 20.93 t ha-1. The treatment also showed the
maximum uptake of N, P and K. Soil available N, P and K status were the highest
in mound method at 30 cm x 30 cm (m5) and on par with m4 and m2. Bacterial,
fungal and actinomycete population and dehydrogenase activity were higher in the
bed/ridge method of planting at 30 cm x 15 cm spacing (m1 and m3).
The combination of 60:30:120 kg NPK ha-1 + PGPR Mix 1 + humic acid
(n1g1) resulted in significantly higher growth attributes (plant height, number of
branches and plant spread) while at 135 DAP, n1g2 recorded the maximum
number of leaves, leaf area per plant, LAI and delayed senescence in both the
years. Physiological parameters (DMP, CGR, RGR, NAR) yield attributes, per
hectare tuber yield, marketable tuber yield, percentage marketable tuber yield, N,
P, K uptake, starch and protein content were superior in n1g1. The tuber yield and
marketable tuber yield (pooled) were 21.10 and 18.34 t ha-1 respectively. Soil
available N, P, K status, microbial count and dehydrogenase activity were
markedly higher in treatments involving PGPR Mix 1 (n1) compared to that
without PGPR Mix 1, nevertheless, remained comparable among n1g1, n1g2 and
n1g3.
Land configuration (bed/ridge) with planting at wider spacing and
inclusion of PGPR and humic acid proved superior with respect to the number of
branches, leaves per plant and leaf area. Leaf area index was significantly the
highest in m3n1g1 in the first year and m1n1g1 in the second year at 90 DAP. The
combination m4n1g1, produced the maximum number of tubers per plant (23.8) in
the first year on par with m2n1g1 (23.6), whereas during the second year it was the
highest (25.0) in m2n1g1. Maximum per plant tuber yield (189.48 and 198.95 g),
marketable tuber yield (170.37 and 179.45 g) and percentage of marketable tubers
(73.06 and 70.67) were noted in m2n1g1 during both years.
The treatment combination m1n1g1 recorded the highest DMP and per
hectare tuber yield with a pooled mean of 23.38 t ha-1. The percentage of
marketable tuber yields increased by nearly 10 per cent over m1n2g3 in the two
years. Potassium uptake was the highest in m1n1g1 and remained comparable with
m1n1g2 in the second year. Irrespective of growth promoters applied, inclusion of
PGPR Mix 1 (n1) resulted in higher soil available P and K status in the widely
spaced planting and the maximum dehydrogenase activity and microbial counts
were enumerated in the closely spaced planting on beds (m1). Bed method of
planting at 30 cm x 15 cm spacing along with application of 60:30:120 kg NPK
ha-1 + PGPR Mix 1 + humic acid (m1n1g1) was the most profitable resource
management practice, pooled mean of economics of cultivation revealed
maximum net returns and BCR of ₹ 651296 ha-1 and 3.83 respectively.
The CO2 fertilization study was conducted in trenches (2 m x 1 m x 1 m)
in completely randomized design with six treatments (substrates for CO2
evolution) replicated thrice, during November 2019- July 2020 and October 2020-
March 2021. The treatments included, s0: no substrate, s1: cow dung, s2: coir pith,
s3: cow dung + coir pith (2:1), s4: s2 + Pleurotus 1g kg-1 + N + P (2% w/w) and s5:
s3 + Pleurotus 1g kg-1 + N + P (2% w/w). Cuttings of Chinese potato were planted
directly in soil in the first year and in grow bags during the second year. Organic
substrates (as per treatment) were spread at the trench base to a thickness of 5 cm,
taking precautions to avoid direct contact of the substrates with the cuttings
planted directly in soil. The trenches were kept covered with a dome prepared of
200 μ uv stabilised polythene sheet fixed on a metal frame, daily from 4.00 pm to
10.30 am.
In all the substrate applied treatments, maximum release of CO2 (501 to
858 ppm) occurred during the first two weeks of application and thereafter it
declined. The highest peak of CO2 concentration (858 ppm) at two weeks of
application was observed in s5 followed by s3, (752 ppm). Relatively higher air
and soil temperatures were observed in trenches during both the years of study.
Significantly higher growth attributes at 30 DAP were observed in plants
grown in the trench filled with cow dung and coir pith in 2:1 ratio (s3) comparable
with treatments containing cow dung and additives (s5). The superiority of s5 on
growth attributes were evident at the later stages of growth. Chlorophyll contents
(1.147 and 1.193 mg g-1) were maximum in s3 applied trenches at 45 DAP,
whereas s5 recorded superior values at 90 DAP (1.153 and 1.193 mg g-1).
Initiation of senescence was significantly earlier in CO2 fertilized plants and the
highest biomass per plant was recorded in s5. Nevertheless, despite an increased
above ground biomass with elevated CO2, tuber development was not observed in
any of the treatments.
Based on the results of the experiments, it could be concluded that bed/
ridge method of land preparation with planting at 30 cm x 30 cm spacing in
combination with an NPK dose of 60:30:120 kg ha-1 + PGPR Mix 1 + humic acid
significantly improved the growth parameters (source) and yield attributes (sink)
in Chinese potato. A closer planting (30 cm x 15 cm) on beds and application of
60:30:120 kg NPK ha-1 through chemical fertilizers, PGPR Mix 1 (2 %) @ 5 g per
plant thrice, as basal, 30 and 60 DAP along with foliar sprays of humic acid @ 5 g
L-1 (45 and 75 DAP) can be recommended for superior marketable tuber yields,
higher net returns and B: C ratio. The results of the CO2 fertilization study
indicated that elevated CO2 enhanced the vegetative growth in Chinese potato at
the expense of tuber development. |
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