Contents - Greenmount Press

applied per cent open bolls were recorded on control plots. At
the same time five plants were taken from each control plot
and all bolls (regardless of size or age) from each plant were
separated into open, mature, and immature bolls using the boll
cutting techniques. Seed cotton was removed from the bolls and
lint collected for HVI analysis after ginning using a miniature hand
operated gin.
At harvest, yield was determined from machine picking.
Samples were ginned and again HVI tested at CSIRO Narrabri.
Results
Changes in the timing of harvest aid application and
differences in conditions across experiments created considerable
variability and inconsistency in fibre quality among boll classes
(Table 1). Generally across experiments, immature bolls had
consistently lower micronaire compared to the mature and
FIGURe 1: Micronaire of the immature bolls
taken at defoliation related to the micronaire
measured at harvest time. Note that the
relationship was improved when the per cent
open bolls was added. Relationships are fitted
to data taken from all experiments combined.
open bolls, and there was greater variation in micronaire across
defoliation times with immature bolls. Fibre quality of boll classes
at similar defoliation times also varied among experiments, and
most likely reflected the differences in the seasonal growing
conditions by all bolls in each class.
Temperature during boll-filling is known to affect micronaire
and each experiment was exposed to differences in their late
season temperatures (February to April). During this period, the
2006–07 experiment 2 had the highest daily average temperature
(24.5˚C) followed by the 2005–06 experiment (23.5˚C), and the
coolest was the 2007–08 experiment 3 (21.3˚C). Micronaire
across harvest aid treatments for all boll classes was lowest in
2007–08 and was highest in 2006–07.
This significant variation and lack of consistent changes in
micronaire with defoliation times within and across boll classes
is conceivable. Samples collected for quality assessment at the
time of defoliation would firstly, differ in their number and
age, and secondly, most likely were exposed to differences in
growing conditions during their development. These factors
would influence fibre quality. Therefore the use of the boll cutting
technique that classifies bolls of similar classes does not imply
that fibre quality will be similar when comparisons of boll classes
are made within a season or between seasons. Nor does it mean
that quality between boll classes will be different. Overall the
TABLe 1: Micronaire for immature, mature,
and open bolls measured at various per cent
open bolls in all experiments at the time of
defoliation
Defoliation
treatment
% open
bolls
Micronaire
Immature Mature Open
Experiment 2005–06
1 29.2 3.75 4.00 4.20
2 41.9 3.60 4.75 4.50
3 56.0 3.45 4.78 4.63
4 68.4 3.35 4.88 4.48
5 76.9 3.95 4.98 4.35
6 85.9 3.42 4.74 4.70
7 93.0 3.73 4.93 4.63
Mean boll class 3.61 4.72 4.50
Experiment 2006–07
1 1.6 3.90 5.53 5.01
2 14.2 4.38 5.23 5.08
3 29.9 4.15 5.43 5.10
4 45.6 4.55 5.23 5.10
5 58.2 4.65 — 5.20
6 73.8 — — 5.18
7 89.5 — — 5.05
Mean boll class 4.33 5.36 5.10
Experiment 2007–08
1 0.6 2.45 4.58 —
2 9.0 2.48 4.35 4.71
3 16.4 2.93 4.08 4.65
4 25.5 2.95 4.08 4.43
5 36.3 3.70 4.00 4.33
6 53.5 3.26 3.88 4.33
Mean boll class 2.96 4.16 4.50
44 — The Australian Cottongrower October–November 2012