Flowering is a Critical Period of Crop Development
Flowering is a critical period of crop development, as this is where the yield potential your crop is established. The length of the flowering period, conditions and stresses encountered during this flowering window will determine the production and retention of bolls, and the fibre quality.
CSD’s STEFF (Simulated Time to Estimated First Flower) is a useful tool to help you estimate the date of first flower.
Alternatively, CottonTracka® is another great CSD tool that can be utilised to monitor and optimise your crops performance.
Figure 1: Example of a cotton plant at January’s peak flowering period.
NODES ABOVE WHITE FLOWER
In order for crops to reach their maximum yield potential, the plants need to be strong enough to produce and hold new flowers whilst having enough resources to fill existing bolls throughout the plant. High yielding crops do not necessarily grow excessively tall or for a long season but they hold onto later bolls at the top of the plant as well as in the outer positions.
Ideally, you should aim for:
- 8+ NAWF at first flower
- Maintain NAWF as long as possible as it indicates that the plant is actively growing
Figure 2: Average NAWF decline for CSD Ambassador Network fields.
PREVENTING EARLY CUT-OUT
The period from flowering to cut out is when up to 90% of the crop yield is set. So, ensuring that the plant/crop grows actively, healthy and with minimal stress through this period is paramount.
A stressed crop limited in resources may result in:
- Slow node development
- NAWF decreasing very rapidly and squares at the top of the plant may be shed
- Reduce the plant’s leaf area which may decrease its capacity to fill bolls.
A crop’s NAWF will however always decrease to a point where it ‘cuts out’ (approx. four NAWF). The limitations on NAWF include the season length, day degrees, and radiation. Overall, to achieve higher yield, the flowering period needs to be extended as long as possible. It is easier to pull a crop up through late season with growth regulator management than it is to nurse it through the season with minimal NAWF.
CAN STRESS DURING JANUARY INFLUENCE BOLL WEIGHT?
The number of ovules in a flower that are fertilised on the day of flowering is a key factor in the number of seeds per boll, and hence the amount of lint per boll. In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. Flowers fertilised during a time of crop stress may have fewer ovules and go on to become light bolls.
Figure 3: 5-years of irrigated CSD Ambassador data, displaying the influence of the length of the flowering period on cotton boll numbers.
BOLL LOAD
Boll numbers can offer a good indicator of how the crop is progressing. Cotton plants will physiologically shed fruit if supply of carbohydrates in the plant is not sufficient to meet the demands of fruit at that particular time. These carbohydrates are directed preferentially to the development of fruit that are already ‘set’. The fruit most susceptible to shedding are:
- Bolls less than 10 days old.
- Small squares.
Bolls older than 14 days are generally not susceptible. The time period post cut-out is used mainly to fill existing bolls with minimal further accumulation in number. If weather forecasts indicate periods of hot weather, irrigations may need to be brought forward to make up for increased evapotranspiration rates. Likewise, the reverse
applies after in-crop rainfall or cooler conditions. Also remember water use per day accelerates at flowering and the crop requires approximately 3ML in both the flowering to cut-out and cut-out to defoliation periods.
Figure 4: Average boll accumulation in high yielding CSD Ambassador Network crops. The black line is crops yielding above 15 b/ha, the red line is crops yielding 12.5 – 15 b/ha and the blue lines is crops yielding 10 – 12.5 b/ha.
Figure 5: Average crop water use segmented into 3 distinct phases of crop development.
© Cotton Seed Distributors Ltd 2022. General guide only; not comprehensive or specific technical advice. Circumstances vary from farm to farm. To the fullest extent permitted by law, CSD expressly disclaims all liability for any loss or damage arising from reliance upon any information, statement or opinion in this document or from any errors or omissions in this document. Roundup Ready Flex®, Roundup Ready®, Bollgard II® and Bollgard® 3 are registered trademarks of Monsanto Technologies LLC, used under licence by Monsanto Australia Ltd. Insect control technology incorporated into these seeds is commercialised under a licence from Syngenta Crop Protection AG. Sicot, Sicala, Siokra and Sipima cotton varieties are a result of a joint venture research program, Cotton Breeding Australia, conducted by CSIRO and Cotton Seed Distributors Ltd (CSD). CSD is a partner in the CottonInfo joint venture, in partnership with Cotton Research Development Corporation and Cotton Australia.