International Journal of Horticulture, 2017, Vol.7, No. 12, 95-105
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stress, yam plants rejuvenate to initiate retuberization. The total yield, early plus final harvest is more than usual
yield due to fast growth of tuber after yam detachment; this is also evident from yam growth curve analysis.
Since early harvest fetches a good price in market, the two stage harvesting procedure with interim harvest, at
about four and half months after sprouting, from yam plants with seed weight 800 g is found to be conducive for
maximising revenue from higher total yield in harsh agro-climatic environment and nominal plant care, with a
few irrigations in extreme summer of Jharkhand.
2 Materials and Methods
We study longitudinal growth of Elephant-foot-yam for sixty plants under extreme agro-climatic stress in a field
experiment conducted in the agricultural farm at Indian Statistical Institute, Giridih, with seed weights 500 g, 650
g and 800 g of yam.
The experimental layout is similar to that described in Dasgupta (2016), this consists of six columns, in each
column there are ten equidistant pits at a distance of 1 m. First two columns are for seed weight 500 g, next two
are for seed weight 650 g, and the last two columns are for plants with seed weight 800 g. Column to column
distance is also 1 m; the plants are numbered 1-10 in the first column, 11-20 in the second etc.
Little vermicompost is given in the pits while planting the fungicide treated cut yam seed corms of specified
weights at the start of the experiment on 20 March 2016. From the start of the experiment we consider a general
plant stress viz., little fertilizer and scanty irrigation.
The average lifetime of yam plants in this experiment is 185.90 days. Due to plant stress induced in the
experiment, the figure is less than plant lifespan average that may be up to 9 months. At about one fourth of that
time period i.e., at about two and half months after sprouting we take first interim growth reading on underground
yam; and at half of the time period of 9 months i.e., at about four and half months from sprouting we take second
interim reading on underground yam in this longitudinal study. Plants are subjected to possible yam detachment
only at the time of interim growth recordings. Uprooting and replanting are done sequentially one by one with
possible yam detachment, to minimise resultant plant stress of aboveground exposure.
With 20 plants in each seed category, all yam plants are subjected to stress of harsh agro-climatic environment.
Further as a severe stress, for some plants in each seed weight category, underground yam associated with root
structure are detached at about two and half months after sprouting, and for some plants yam detachment is at
about four and half months after sprouting, and for remaining plants no interim yam detachment is made;
decision of detachment is based on an assessment of underground yam growth at the time of interim recording.
For plants with yam detached, stem structure with a few roots still attached near the base of stems are replanted
immediately in the same pit to continue experiment. For plants in each seed weight category under general stress,
interim yam readings are recorded by taking plants off the ground with care, and underground yam volumes are
measured by Archimedean principle of water displacement and the experiment is continued after replanting in the
same pit. Yam weight is indirectly estimated by multiplying the volume of yam, obtained from Archimedean
principle of displaced water volume, when only the yam part of a plant is immersed in a water container. Yam
volume multiplied by density (≈ 4 g /c.c) provides an estimate of yam weight in non-destructive testing.
Plants are subjected to two interim yam growth measurements, if found alive at the time of measurements i.e.,
after about two and half months from sprouting, and after about four and half months from sprouting. At most
one yam detachment per plant during the experiment is made. Some plants are left undisturbed of yam
detachment till the end for comparison with other strategies.
When yams are not detached from stems, stress is considered moderate for plants. In the present study the time of
first intervention is on 30 July 2016. The second intervention is on 28 September 2016.
