This investigation was undertaken to study the optimum plot size, number of
replications and number of sampling units for faba bean yield trials at Sids Agric.
Research Station during 2002/2003 and 2003/2004 seasons. The experiment
included 7 genotypes of faba bean cultivars. A randomized complete block design
with three replications was selected. The area of each plot was 7.2 m2• Data were
subjected by two procedures, the first method was developed by Smith (1938) and
the second method was the maximum curvature developed by Lessman and Atkins
(1963).
The results obtained could be summarized as follows:
Increasing plot size decreased the variance per basic unit and the coefficient of
variability. However, the reduction was not in proportion with the increase in plot
size.
The index of soil variability ranged from -0.512 to -0.807 with an average of -
0.660
The exponential relationships between the coefficient of variability (C.v.) and plot
size (X) were:
C.v.= 18.293 X-O.624 for the first season.
C.v.= 16.318 X-0.860 for the second season.
• The optimum plot size was resulted by two methods as follows:
1- Smith's method: The optimum plot size was 2.441 and 3.218 m2 in the first and
second seasons, respectively.
11- Maximum curvature method: The optimum plot size was 13.342 and 17.648 m2 in
the first and second seasons, respectively.
Increasing plot size and/or number of replications reduced the magnitude of
difference detected at specified level of significance. The reduction of difference
with increasing plot size was less than that obtained by equivalent increase in the
number of replications.
The standard error for the studied characters decreased as number of sample
units or replicates increased.
Number of plants required to detect 10% change between means were markedly
decreased as number of replicates increased.
The optimum number of sample units differed from character to another and it
was greatly affected by number of replications.