Document Type : Research articles.
Authors
1
Agronomy Department, Faculty of Agriculture, Fayoum University
2
Central Laboratory for Design &Statistical Analysis Research,Agriculture Research Center ,Giza,Egypt
Abstract
In the present work, two uniformity trials were carried out during the
first and the second winter seasons of 2011/2012 and 2012/2013 in the
Experimental farm Demo, Faculty of Agriculture, Fayoum University. The
main objectives were to estimate the optimum plot size, plot shape and
number of replicates for wheat yield traits using the variety Sakha 93 as plant
material. The cultivated area of each field trial was divided into 12 strips;
each of which consisted of 100 rows, 0.2 m width and 3.0 m long. Two
statistical methods including soil variability index and maximum curvature
were used to estimate the optimum plot size and shape using the yield data of
1200 basic units (each of 0.6 m2). The data were subjected to two procedures
of statistical analysis to estimate the optimum plot size, when the cost of
conducting the experiment is not taken into consideration and to evaluate the
effect of changing the plot shape on the variability. The first statistical method
was that of maximum curvature which is based on the exponential
relationship between plot size and the coefficient of variability. The second
method was that developed by smith’s method (1938). Bartlett's test for
homogeneity of variances, as outlined by Steel and Torrie (1980), was used
to study the effect of changing plot shape. The obtained results could be
summarized as follows: Increasing the 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 0.6433 to 0.6018 as an average for the 1st and the 2nd seasons,
respectively. The relationship between the coefficient of variability (C.V.)
and plot size (X) were mathematically expressed by the following equation
C.V. = 19.21 X-0.2595 for the 1st season and C.V. = 19.60 X – 0.2725 for the 2nd
one. Accordingly, using the soil variability index, the optimum plot size was
2 basic units (1/3500 fed.) for the two seasons, while it was 4 basic units
(1/1750 fed.) in both seasons when the maximum curvature method was
applied. The required number of replications for the optimum plot size using
Smith method detecting a 15% difference among treatment means varied 13
and 14 in the 1st and the 2nd seasons, respectively. But, for detecting a 20%
difference among treatment means, 7 replications in the 1st season and 8
replications in the 2nd one were found necessary. Optimum plot size estimated
using the maximum curvature method detecting a 15% difference among
treatment means varied 7 and 8 in the 1st and the 2nd seasons, respectively. But, for detecting a 20% difference among treatment means, 4 replications in
the 1st and 2nd season's one were found necessary. Generally, the plot shape
did not affect on the precision of wheat yield trial in most cases in the two
growing seasons.
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