International Journal of Horticulture, 2017, Vol.7, No. 12, 95-105
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With extreme plant stress, more severe than that described in Dasgupta (2016), higher seed weight 800 g comes
to the forefront of yam yield, surpassing the seed weight 650 g of the previous experiments. With interim
detachment around four and half month after sprouting; plants of higher seed weight can cope better with extreme
plant stress for survival, and achieve higher total yield in a harsher agro-climatic environment.
For quantification of the advantage in yam yield when two strategies are compared, one may consider
nonparametric Hodges-Lehmann estimator, see Hodges and Lehmann (1963). This statistic is an estimate of the
difference between two populations. For two sets of data with m and n observations, the set of two-element sets
made contains (m x n) pairs of points, one from each set; each such pair defines one difference of values. The
Hodges-Lehmann statistic is the median of these mn differences. This estimates the differences between the
populations of the paired random variables drawn respectively from the populations.
For seed weight 500 g, total yield (in kg) i.e., interim yield plus final yield on plant maturity from 8 yam plants,
with yam detached at second interim recording are: 1.186, 0.873, 0.620, 0.298, 0.787, 0.532, 0.598, 0.787.
For the same seed weight 500 g, yield (in kg) from 11 mature plants with no interim detachment are: 0.267, 0.128,
0.122, 0.12, 0.158, 0.539, 0.541, 0.502, 0.162, 0.294, 0.736.
One plant of seed weight 500 g had yam cut at first interim growth recording. The 88 values of the differences i.e.,
yam yield with detachment at second interim recording minus yield from undisturbed yam growth with no
detachment has median value 0.407 kg. This is a substantial additional amount per plant with seed weight 500 g.
Thus for the plants with seed weight 500 g, the gain in yield on an average for following the strategy of interim
yam detachment at the time of second growth recording i.e., at about four and half months from sprouting;
compared to usual yield from single harvest at the end of plant maturity is 407 g, per plant.
For seed weight 650 g, total yield with cut at second interim minus yield with cut at first interim has median
value 0.213 kg; for same seed weight total yield with cut at second interim minus yield of undisturbed growth
with no cut has median value 0.0935 kg.
For seed weight 800 g, total yield with cut at second interim minus yield with cut at first interim has median
value 0.3645 kg; for same seed weight total yield with cut at second interim minus yield of undisturbed growth
with no cut has median value 0.2715 kg.
The agro-climatic environment is harsher in the present experiment in comparison with that considered in
Dasgupta (2016) where seed weight 650 g with interim yam detachment in the middle of experimental duration
showed an additional yield of 457 g per plant, compared to conventional single harvest on plant maturity.
It appears that second interim cut is a good strategy to increase yield in all the seed weights we considered, the
additional amount of yam yield per plant going up to 407 g, when interim cut for yam at the time of second
reading is taken recourse to, compared with other harvesting strategies.
3.2 Superior status of yield with yam detachment at the time of second interim growth recording
Yam growth curves for all seed weights and for each seed weight separately are shown in Figure 1, Figure 2,
Figure 3, and Figure 4.
Except for Figure 2 with seed weight 500 g, a general upward trend in growth is seen in these figures.
Figure 5, Figure 6, and Figure 7 show the growth curves of yam in three situations with first interim cut, second
interim cut, and for undisturbed yam with no interim cut respectively, for plants with seed weight 500 g. Figure 5
has a single curve from a plant with first interim cut, as no substantial yam deposition was seen at that early stage
in other plants with low seed weight. The figures indicate that the response curve with second interim cut in
Figure 6, based on mean /median of observations
y
for fixed time
x,
is superior among these three situations.
