Agriculture Reference
In-Depth Information
achieved by
rolling benches
where plants are grown
on benches that can be easily moved to allow access,
but minimizes the greenhouse space that is allocated to
walkways. Rolling benches can, however, cause prob-
lems in cases where plants are tall and require staking
and tying or else they will fall over and be damaged.
In addition, rolling benches can increase the need for
uniform lighting over the whole greenhouse area rather
than only over designated growth areas or static benches.
a basis for the practices used in the plot trials. Factors
that need to be determined include:
•
Land preparations
•
Seeding
rate,
final
plant
density
and
depth
of
planting
•
Nutrient levels and when nutrients are available
(pre-plant and/or post emergence)
•
Irrigation management
•
Timing of operations such as planting and harvest
windows
Experimental design in the glasshouse
•
Chemicals available, for example what insecticides,
fungicides or herbicides are registered for use on
the crop, at what rates they are applied, what seed
treatments are?
One final note on the use of greenhouses and plant
breeding relates to experimental design. Many believe
that the conditions in greenhouses are such that there
is uniformity in soil type, lighting, irrigation etc. In
comparison to conditions that may prevail in the field,
there may indeed be less environmental variation in a
greenhouse. Despite this, it should be noted that there
will be differences nonetheless between, say, plants next
to the glass and those in the centre of the house. There-
fore
all
experiments grown in greenhouses should be
treated with a clear understanding of the fact of vari-
ability in environmental variables exists, and therefore
good experimental design, replication and randomiza-
tion will be as important in greenhouse experiments as
in other situations.
•
Regions where the new cultivars will be targeted
Do not forget, the major aim of field trials is to
mimic
what would happen in commercial agriculture
. There-
fore field trials should usually be planted at the same
time that the crop is normally planted. Planting depth,
plant density, nutrient management, weed control, dis-
ease control, harvest time and method and post-harvest
treatment should all match commercial production as
far as this can be achieved within the restraints of small
plot management.
Choice of land
FIELD PLOT TECHNIQUES
In order to choose a good area of land for field plots
it is necessary to identify the factors that magnify soil
differences and to reduce, if possible, soil heterogeneity.
Fertility gradients are generally more common in
sloping land. Soil nutrients are soluble in water and
tend to settle in the lower land areas. Therefore these
lower soils tend to be more fertile than the higher areas.
An ideal experimental site will be on flat land but this is
not always possible. For example, how many fields have
you seen that are as flat as a football pitch?
If the land has previously been used for plot exper-
iments, then this can lead to increased soil hetero-
geneity. Therefore areas of land that have previously
been planted to different crops, different and var-
ied fertility regimes, or subjected to varying cultural
practices, should be avoided, if possible. In cases
where this has occurred, then the area should be
planted with a uniform crop, with uniform manage-
ment and fertilization for at least two years before it is
A large proportion of the work in a plant breeding pro-
gramme is carried out using field trials. The aim of plant
breeding is to develop superior cultivars that are genet-
ically more adapted than the cultivars that are already
available. New, and old, cultivars are grown within agri-
cultural systems on a large scale. For example, wheat
grown in the Pacific Northwest is grown in fields, which
cover many hundreds of acres. Obviously it is not pos-
sible to evaluate the many thousands of potential new
cultivars in a plant breeding scheme on the large field
areas that they will eventually be grown if successful.
The aim therefore of field trialling is to
predict
how
each genotype would perform
if they were grown on a
large acreage basis
.
In order to grow accurate and representative field plot
trials it is necessary to first determine the way that the
crop is grown in agriculture and to try and use this as
