MSc

A study titled “Performance and allelopathic effect of sweet potato in double
cropped lowlands”was conducted at College of Agriculture, Vellayani and Integrated
Farming System Research Station, Karamana during the period from April 2020 to
November 2020 with the objectives of evaluating the performance of sweet potato
varieties in summer rice fallow, assessing their allelopathic effects on weeds and
examining the residual effect on succeeding virippu rice crop in double cropped lowland
rice based cropping system.
The study comprised three experiments. Experiment-I was a laboratory
bioassay, to assess the allelopathic effect of leaf leachates different varieties of sweet
potato on rice var.Uma, laid out in completely randomized design (factorial CRD),
with three replications. The two factors involved in the experiment were leaf leachate
of different varieties and various concentrations. There were a total of 24 (Leaf leachate
of 8 varieties) x (3 concentrations viz. 1: 5, 1:10 and 1:15 w/v) treatment combinations
and one control (tap water). The varieties selected were Sree Kanaka, Sree Varun, Sree
Arun, Sree Nandini, Sree Bhadra, Bhu Sona, Bhu Krishna and Kanjanghad. The
parameters recordedwere germination percentage, days required for 50 per cent
germination, germination index, plumule length, radicle length, response index, pH of
leachates and phenol and tannin content of leachates.
Experiment-II was a field experiment conducted by raising sweet potato
varieties in double cropped lowland during the summer. Randomized block design
(RBD) was adopted for this experiment with three replications. The treatments were the
eight sweet potato varieties and one fallow treatment as control.
Experiment-III was a field experiment aimed at examining the residual effect of
sweet potato crop by raising rice crop in the same plots where experiment-II was
conducted. Thus, the treatments of this experiment were same as that of experiment-II.
Germination percentage was not significantly affected by the leaf leachates of
different sweet potato varieties or the leachate concentration. The highest germination
index was recorded in Sree Arun (1.87) and lowest in Bhu Krishna (1.59). Plumule
length was maximum in treatment Sree Bhadra (4.6 cm) and lowest for Bhu Sona (3.93
87
cm). Control showed significantly greater plumule length (5.08 cm) than treatments.
Maximum radicle length was observed in Sree Bhadra (8.93 cm) which was on par with
Sree Kanaka and Sree Nandini. With respect to concentration of the leachates, radicle
length was the greatest in 1:15 (w/v) (8.73 cm) and least in 1:5 (W/V) (8.14 cm).
pH of all the leaf leachates were lower when compared to the control. Phenol
content was the highest in leaf leachates of Bhu Krishna (2.34, 2.19 and 1.96 mg 100g1
at 1:5, 1:10 and 1:15 concentration levels respectively) followed by Bhu Sona. The
maximum tannin content was observed in leaf leachate of Bhu Sona (80.40, 71.70,
63.57 mg 100g-1
at 1:5, 1:10 and 1:15 concentration levels respectively).
Grass weeds were the most prevalent in the field. Among grasses, population of
Leptochloa chinensis and Echinochloa crus-galli significantly differed among the
treatments. The population of different species of broad-leaved weeds and sedges did
not differ significantly among treatments.
In case of grasses, the highest weed count was seen in the control (210.67) which
was on par with Sree Bhadra and Bhu Sona. The lowest weed dry weight was in Sree
Arun (9.37 g m-2
) which was on par with Kanjanghad, Bhu Krishna, Sree Nandini and
Sree Varun. The highest weed control efficiency was observed in Sree Arun (45.97 %)
which was on par with Bhu Krishna (45.19 %).
At 20 DAP, the dry matter production (DMP) was comparable among the sweet
potato varieties. At 40 DAP, the highest dry matter production was observed in Sree
Varun (35.97 g/plant) which was on par with Bhu Krishna and Sree Arun. At 60 DAP,
maximum DMP was seen in Bhu Krishna (46.85 g/plant) and was on par with Sree
Varun and Kanjanghad. At harvest, Bhu Krishna had maximum DMP (52.09 g/plant)
and was on par with Sree Varun (50.13 g/plant). Crop growth rate (CGR), during the
period of 40 to 60 DAP alone, was significantly higher in Bhu Krishna
(4.57 g m-2 day-1
) and it was on par with Kanjanghad (4.49 g m-2 day-1
) and Sree Varun
(3.63 g m-2 day-1
). Relative growth rate (RGR), during the period of 40 DAP to 60 DAP
alone, was highest in Kanjanghad (14.06 x 10-3
g g-1
day-1
) and it was on par with Bhu
Krishna (13.28 14.06 x 10-3
g g-1
day-1
) and Sree Nandini (11.21 14.06 x 10-3
g g-1
day-1
). At 40 DAP, the SPAD value was the highest for Sree Varun (39.07) which was
on par with all treatments, except Sree Bhadra and Sree Arun. At 60 DAP, SPAD value
88
was the highest in Sree Nandini (40.03) which was on par with Kanjanghad, Bhu
Krishna and Sree Varun.
Post-harvest soil analysis revealed the lowest soil pH in control (5.25), Bhu
Krishna, Sree Varun and Sree Kanaka all of which were on par. The highest organic
carbon content was noticed in Sree Arun (1.36 %) which was commensurate with Bhu
Krishna, Sree Nandini and Sree Varun. The highest available nitrogen content was
observed in Bhu Sona (215.12 kg ha-1
) which was similar to Kanjanghad, Bhu Krishna,
Sree Bhadra and Sree Nandini. The highest available potassium content was observed
in Bhu Sona (85.17 kg ha-1
) and it was on par with control plot, Sree Bhadra, Sree
Nandini and Sree Kanaka.
Highest gross income, net income and benefit:cost ratio were obtained from
Kanjanghad which was on par with Bhu Krishna and Sree Varun.
Highest rice grain yield was obtained in the crop that followed Kanjanghad
(2103.17 kg ha-1
) which was on par with that which followed Bhu Krishna and Sree
Arun. There was no significant difference in straw yield between treatments.
Hence, from the experiments it can be concluded that Bhu Sona and Bhu Krishna
varieties exerted a greater inhibitory allelopathic effect on rice seedling growth
compared to other varieties. Among the varieties, Sree Arun (upto 64 %) and Bhu
Krishna (upto 61 %) suppressed weed growth more with higher weed control efficiency.
Evaluation of sweet potato varieties in summer fallows of double cropped lowland
revealed that Bhu Krishna, Kanjanghad and Sree Varun performed better with respect
to yield attributes, yield and economics. In the virippu rice crop raised to assess residual
effect, higher yield was obtained the crop which succeeded Bhu Krishna, while the
lowest yield was observed in crop that followed Bhu Sona.