Page 17 - 08 Cotton SA March 2016

Continue from p 16 fiNishiNG the CroP With liMited Water

backwards. To force a boll open prior to maturity it needs to defoliation. Growth regulators applied at last effective flower
be approximately 75% (approx. 500-550 day degrees) through assist with minimising non productive growth and allow those
development. Therefore on average you will need to feed and resources to be available to support growth of bolls (yield),
water from flowering for 38-40 days to get it into the picker. especially in situations where crops have more than ample
nutrition.
Hot Weather: It will increase water use per day and therefore
the crop water requirement is higher which in turn reduces the Crop Stress Responses: At this time the crop is principally
number of days of available moisture for maturing bolls. On filling bolls, and is past the more sensitive periods of crop
average the crop will use 8mm per day till defoliation - a higher development such as leaf growth, rate of squaring or crop
amount now during boll fill and less as the crop opens up. height determination. The least sensitive development phase to
water stress is boll growth, and this is the one factor which is still
Premature Plant Stress: By stretching irrigations to prolong relevant at this time of the crop’s growth.
the life of the crop, there is a risk of the crop going into stress
prematurely. Remember that stretching irrigations will require
more water in the subsequent irrigations and it will take longer
to come through which impacts down the line of the irrigation COUPLE OF SCENARIOS
cycle, hence crops may stress further waiting their turn. Stretching
irrigations late in the flowering period has the greatest impact Let’s use the example plant in FIGURE 1 as a guide with two
on yield, postponing this stress to boll maturation is where the irrigations to go, and the third last irrigation just applied (180
stress will have the least impact. mm). Assume that a boll will open if it is 75% mature (40 days
old).
In this example the crop in scenario B needs to have its cut
WHAT IS GOING TO WORK FOR YOU out application of Pix now. The flower numbered 24 is the last
effective flower for this crop, anything above this flower has little
Fibre Quality: Modern Australian cotton varieties with chance of making the picker.
the exception of Sicot 71RRF have very good fibre quality
characteristics, so they provide some buffering before penalties The crop in scenario A will require to be shut down just prior to
occur. In addition later stress means that there is less impact on the next irrigation. In this example target the square numbered
fibre length. 15, as this will be the last effective flower in this crop. In both
these scenarios that will enable 40 days to mature that last boll
Soil Moisture: One of the most under utilised resources by cotton on the plant so it will open and contribute to yield.
growers is residual soil moisture. Industry recommendations
in the past have used the guideline of being at refill point at
defoliation to assist with boll maturation and leaf drop. Later in
crop growth more of this stored soil moisture could be utilised,
between refill point and wilting point of the soil. However, crops
should not be overly stressed so that effective defoliation can
still occur. As well, drying out the soil moisture profile to wilting
point may assist in minimising damage to soil structure through
picker compaction.

Growth Regulators: Many have adopted the practice of
applying high rates of growth regulators at cutout to reduce
excessive late season growth and boost crop uniformity into

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