MSc

The study entitled "Trends in production and bienniality of coconut (Cocos nucifera L.) var.WCT"
was carried out based on data on the number of nuts
harvested from 525 WCT palms planted in 1966 at Coconut Research Station,
Balaramapuram with its five to six harvests per year, for a period of 25 years viz.
1993 to 2017. The objectives of the study are to identify the extent of bienniality,
variations in repeatability and type of yield fluctuations over years and over different
harvests. The effect of meteorological factors like rainfall, number of rainy days,
maximum and minimum temperature and wind velocity of the above period also
formed part of this study.
Initial data analysis using box plot technique was carried out to remove the
outliers present in the data. The number of nuts produced by a palm in an year was
found to be 68.5 with an overall standard deviation of 37.83 nuts. A plot of the
average number of nuts produced in an year against the growing periods showed a
steady decrease in yield from 2012 onwards (i.e. after 50 years of planting).
Preliminary statistical analysis by applying Analysis of variance (ANOVA) for the
number of nuts produced by individual palms revealed high significant difference
between different palms with respect to each harvest and also with respect to each
year.
Pearson’s correlation coefficient between yield data of different harvests in an
year as well as previous years were estimated and a significant correlation were
observed for the previous harvest and rest of the coefficient were non significant.
Statistical tools in respect of graphical, parametric and non parametric approaches
were tried as an attempt to detect and quantify the biennial bearing tendency.
Graphical approach confirmed biennial bearing tendency among different years as
well as among different harvests.
The parametric study was carried out using orthogonal contrasts developed by
Saraswathi (1983). This method used four F ratios F1, F2, F3 and F4 , the significance
of which provide biennial tendency and time-trend each for four year periods. F1 ratio
is used to test the biennial tendency under the assumption of absence of time trend
and then
confirmed by F2 ratio. F3 is used to test time trend effect under the
assumption of absence of biennial effect. This assumption confirmed by F4 ratio. For
the period 1997-2000, F1 was found to be significant at 5 per cent level indicating
biennial tendency for this period in the absence of time trend, which was then
confirmed using F2 criterion. But this method didn’t confirm bienniality for other
periods
The non parametric approach using biennial bearing index ‘B’ (Hoblyn et al.,
1936) was made for the period of 1993-2017. The ‘B’ factor was based on 23 pairs
of successive signs positive or negative indicating fall or rise in yield over continuous
years for each of the palms. A test of significance of bienniality was obtained by
calculating the binomial probabilities. Number of successive change in signs of 16 or
above for this period indicate significant departure from the equiprobable hypothesis.
Therefore a palm showing a B factor equal to or higher than 16/23 can consider as
significantly biennial in bearing; and on this basis 41.1 per cent of the palms were
found to be biennial in bearing.
Intensity or degree of crop fluctuations was measured by the ‘I’ factor
(Hoblyn et al., 1936). All palms showed an intensity of crop fluctuations less than 50
per cent; of which in 81.8 per cent, the intensity ranged from 20 to 30 per cent. A
zero percent ‘I’ indicates regular bearing or no alternate bearing behavior. Regular
bearing was not observed for any of the palms. 100 per cent I indicates strict alternate
bearing behavior. No palms were found to be strict in alternate
bearing also.
Maximum number of palms were found to exhibit the biennial bearing pattern but are
not strict ( 100 per cent) in bienniality.
Spearman’s rank correlation coefficients were calculated for all 23 pair of
alternate years and all 24 pair of adjacent years. For palms possessing biennial
tendency the coefficients for alternate years should be higher than that of adjacent
years and this is tested by rank sum test (Z). The Z value was found to be non
significant for the period 1993-2017 indicating no strict alternate bearing behavior in
the selected palms. As production is found to be in a a steady decrease from 2002
onwards ‘Z’ is separately estimated for the period 1993-2001, and found to be
significant for this period indicating alternate bearing behavior for this period.
Repeatability was estimated for number of nuts per tree using ANOVA
estimator for different periods. While considering the whole period 1993-2017 and
2013-2016 repeatability coefficient was very low 0.13 and 0.06 respectively with
variances 0.00015 and 0.00052 respectively. High estimate of repeatability, 0.397,
0.355 respectively were observed for the period 1993-1996 and1997-2000.
Correlation between climatic factors in the current year, previous year, two
years before and three years before with the production of nuts for the current year
were estimated and were not significant except for the minimum temperature of the
current year. It indicated that the parameters of annual climatic factors were not
adequate to explain the temporal variation in yield. However Correlation between
number of days without rain in summer (dry spell ) and yield in succeeding season of
next year was found to be -0.43 which is negatively significant, showing this factor
will inversely affect the yield of the next harvest. Bienniality also found to be not
directly influenced by the climatic factors. A linear regression model with high R2
value, 0.98 were fitted with current year yield as dependent variables and previous
year yield, Number of trees in the ‘on’ phase, Rainy days and Wind velocity as
independent variables.