Agriculture Reference
In-Depth Information
Randomized Block Design or Randomized
Complete Block Design (RBD/RCBD)
A randomized complete block design (RCBD) or
simply randomized block design (RBD) is the
most widely used design which takes into
account the variability among the experimental
units. A randomized block design uses all the
three basic principles of experimental design,
namely, (1) replication, (2) randomization, and
(3) local control. In RBD, the whole variation is
partitioned into mainly three components: (a)
due to factors that are varied by an experimenter
at his/her own wish, (b) due to variability in
experimental units, and (c) due to extraneous
factors—the experimental error. As such, a two-
way analysis of variance is being followed. In a
randomized block design, the whole experimen-
tal area is divided into a number of homogeneous
block/groups, and each block/group consists of
as many experimental units as the number of
treatments. Blocking/grouping is done in such a
way that the variation among the experimental
units within the block/group is minimum (homo-
geneous) and the variation among the experimen-
tal units of different blocks/groups is maximum
(heterogeneous).
Latin Square Design
In some experimental areas, it is found that soil
heterogeneity varies in two perpendicular
directions, that is, north to south and east to
west or south to north and west to east, or indi-
vidual units can be grouped based on the two
variable characteristics. BD cannot take care of
such methodology; LSD has the capacity to han-
dle two sources of variations independently from
the blocking criterion as in the case of RBD. A
Latin square is an arrangement of treatments in
such a way that each treatment occurs once and
only once in each row and each column. Because
of this type of allocation of treatments, the total
variations among the experimental units are
partitioned into different sources, namely, row,
column, treatments, and errors. If the number of
treatments is also equal to the number of
replications r for each treatment, then the total
number of experimental units needed for this
design is t x t. These t
2
units are arranged in
t rows and t columns and the resulting LSD is
an incomplete three-way design.
This type of experiment is mostly conducted or
useful in field conditions or greenhouse
conditions. The condition for the appearance of a
treatment once and only once in each row and
in each column can be achieved only if the number
of replications is equal to the number of
treatments, thereby is equal to the number of
rows and columns treatments to be taken under
LSD. This limits the LSD design's applicability in
field experimentations. The number of treatments
in LSD design should not be too many or too few.
All these limitations have resulted in the limited
use of Latin square design, in spite of its high
potential in controlling experimental errors.
Advantages
1. RBD is the simplest of all block designs.
2. Its layout is very simple.
3. It uses all the three principles of design of
experiments.
4. It is more efficient compared to CRD.
Disadvantages
1. The number of treatments cannot be very
large. If the number of treatments is very
large, then it is very difficult to have a greater
homogeneous block/group to accommodate
all the treatments. In practice, the number of
treatments in RBD should not exceed 12.
2. Like CRD, flexibility of using variable repli-
cation for different treatments is not possible.
3. Missing observation, if any, is to be estimated
first and then analysis of data is to be
undertaken.
4. It takes care of the heterogeneity of an experi-
mental area in one direction only.
Advantages and Disadvantages
Advantages
Latin square design is an improvement over the
other two basic designs, CRD and RBD, as it
takes care of the heterogeneity or the two-way
variations. Sometimes, when an experimenter
does not have an idea about the soil heteroge-
neity among the experimental units or does
not have the time to check the heterogeneity
pattern, he/she can opt for the LSD design.
