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Steering Tomatoes In
the wild, tomatoes tend to grow vegetatively (growing stems and leaves)
when they are young plants in spring but when they have grown to a
reasonable size going into summer, change to generative growing (most
effort put into flowers, buds and fruit).
Modern
tomato growers, however, want to grow the plants for 10 or more months,
right into winter when prices are high.
To do this they need to steer the plants away from its natural
tendency to grow too generatively in summer and also to avoid it becoming
too vegetative in cool, low light conditions as winter is approached.
Growers call this balancing the plant and spend considerable time
and energy achieving this as it has a major effect on quality, disease
control and yield. In
addition, optimizing the watering regimen minimizes wastage of water and
fertilizer and reduces harm to the environment. Warm,
high light, low humidity, summer conditions steer the plant toward
generative growth and cooler, lower light conditions toward more
vegetative growth. This means
that it is difficult to keep the plants growing with some vegetative
tendency in summer and to stop them becoming too vegetative in cooler,
dull conditions. At
these times, manipulating the root zone conditions in conjunction with
environmental conditions can be particularly advantageous. Environmental Root-zone Environmental Root-zone Things
are not as simple as that though, as excesses of some of these influences
can create other problems and sensible limits must be applied.
In fact, many of the changes that can steer toward vegetative can
also cause fruit split or cause disease problems if overdone especially if
implemented after conditions have allowed to become too generative for any
period of time. Much
steering can be done by adjusting the irrigation EC (increase in low light
conditions and lower in bright conditions),
by adjusting the watering start and stop times and by changing the
irrigation duration and frequency. For
night dry down, it is normally considered that a dry down of 4 to 6% will
be vegetative and 8 to 12% will be generative.
Lower than 4% and you might be looking at poor root development and
subsequent disease problems. Too
dry and it will be difficult to wet up again the next day. In general,
changes to the media moisture content should be made slowly at say 1%
change per day. The
watering start time must be close to sunrise - certainly no later than 2
hours after sunrise.
Too close to sunrise or before sunrise and there is a risk of splitting the fruit.
Too far after sun rise, may make it difficult to wet up for the day
as the crop will already be taking water from the media before watering
commences. The
watering stop time is frequently manipulated to steer the plant.
Stopping earlier will cause greater dry down and steer toward
generative. The average time
to stop is when it is estimated that there will be a further 200 to 300
Joules/cm2 of light energy received before dusk.
Obviously, this has to be an estimation based on expected weather
and previous days experience, watching carefully to see what dry down was
actually achieved the night(s) before.
The exact setting will also depend on the growers observations ie
is the crop. Measure
length between highest flower truss and growing tip (long = veg; short
= gen) For
some common tomato varieties, the flower truss to tip is typically about
14cm and the stem diameter is 10 or 11mm for a “balanced” plant.
The
other correction to make is to check the irrigation start time is not too
late and also adjust the stop time to ensure there is not excessive dry
down overnight. Normally,
stop time is set to about 2hours (or 250J/cm2)
before sunset hoping to achieve a dry down of between 2% to 4% by
sunset. Whilst
this article may provide the grower with a better understanding of some of
the general principles of crop steering by root-zone control, it is
important to get advice from a horticultural consultant that is familiar
with the particular climate and crop variety.
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