Factors that affect Cotton Establishment
Achieving even establishment of a cotton crop is critical in getting the crop off to a good start. Growers should aim to plant the crop once, achieve the desired plant stand and evenness, and get the crop off to a great start.
FACTORS WHICH LEAD TO INCREASED SEEDLING MORTALITY
Field and Bed Conditions at Planting
Through research funded by the FastStart Research & Development Fund (a collaboration between CSD and Syngenta) and in partnership with the CSIRO, CSD have been studying what the ideal planting conditions are for dryland and irrigated cotton. By examining soil strength, dispersion potential, stubble and trash levels, clod size and distribution, moisture content and bed consolidation over the past few seasons, the CSD Extension and Development team have witnessed a considerable variation in
the establishment achieved by growers within the CSD Ambassador Network and trial programs.
Figure 1 shows the establishment results from 362 crops across 7 planting years ranging from 22% to 100% based on planting date. The same seed lot can produce variable establishment depending on the field and planting conditions. Year on year, CSD sees a lot of variability in the trial program and Ambassador Network in terms of establishment percentage. These are the same seed lots with similar germination percentage, but the result is not the same. It highlights that there are a number of different aspects which contribute to successful establishment.
Fields within the CSD Ambassador Network were scored on a scale of 1-5 for seed bed conditions with one being ideal conditions, good consolidated beds with consistent small clod size, free of weeds and stubble. A score of five was for back to back conditions with large clods and heavy loads of trash on the surface.
When the scores were plotted against establishment percentages, it highlighted a relationship with the higher establishment in better seed bed conditions (as seen in Figure 2). However, it should be noted although the overall trend is negative, there is a lot of variability in the establishment results especially at level two and three, inferring further influences on establishment. Table 1 provides a simplified example the average establishment based on their field score.
Uneven or cloddy conditions can result in uneven seed placement, poor seed/soil and therefore seed/moisture contact, resulting in staggered germination and gappy stands. In watered up situations, seed movement deeper into the soil profile has also been recorded. Uneven planting depth can be exacerbated by planting at too fast a speed for the conditions, causing excessive bounce and vibration in the planter unit and an uneven traverse across the field.
The amounts of stubble cover, cotton trash and its fate post the planter passing will also have an impact on seed establishment. Worst case scenarios are when trash falls into the planting slot. Growers should ensure options such as trash wipers are benefiting the planting operation as required.
It should also be noted that less than ideal field conditions can be overcome to achieve good establishment. Good establishment results have been witnessed when planting speed is reduced to maintain accurate seed depth, the traffic light temperature recommendation is followed and care is taken in irrigating to establish the crop.
Table 1: An example the average establishment based on their field score.
Soil insects such as wireworm in particular, can attack young seedlings. Soil insect pests should be scouted prior to planting. Some seed treatment insecticides will control them but because the insect needs to feed on the plant before it dies, some plant stand loss can still occur. Special attention should be given to fields with high levels of cereal stubble or residual weeds.
Having a full understanding of the activity of the seed insecticide treatment applied and the length of residual activity of each product, and having knowledge of field levels of insects, will inform decisions on if additional protection is required. In situations where high levels of soil insects are present, additional application of granular insecticide or liquid insecticide injected into the planting slot should be considered to offer further protection to the emerging seedling.
Rhizoctonia, Pythium and Fusarium can kill young plants during and after emergence. Black root rot slows crop development and reduces season length, and if present this must be allowed and compensated for. These diseases are more prevalent at lower temperatures, where there are high levels of cotton residue in the fields and in fields with a history of disease symptoms.
In situations where seedling disease pressures are high and/or planting temperature conditions are less than desirable, in-furrow additional fungicide treatments similar to insecticide applications can be considered to further protect the germinating and emerging seedling.
EFFECT OF TEMPERATURE ON GERMINATION
Temperature plays a vital role in the rate of development and germination of a cotton seedling. Cotton is a temperature sensitive crop and the way the crop deals with the extremes of temperature is by shutting down or slowing physiological processes in the plant. Below 12°C, the growth of a cotton plant is severely retarded and enzymatic activity within the cotton plant does not function properly until temperatures are above 15°C.
Temperature experienced post planting will also have an impact on the time taken for the plant to emerge. The slower the plant grows, the greater the chance of seedling death occurring through disease and insect damage. Figure 3 illustrates the critical time of an early seedling’s life in terms of sensitivity to cold temperatures.
This is why it is so important to monitor soil and air temperatures to find the appropriate window to plant the crop. It has been an Australian cotton industry guideline for many years that cotton planting should not begin before soil temperatures reach 14°C or above at 10 cm depth, at 8.00am. Planting at temperatures below this will diminish root and shoot growth, reduce water and nutrient uptake and make plants much more susceptible to attack from seedling diseases and insects.
As the cotton plant emerges faster and starts to generate its own energy from sunlight. Root growth is rapid, minimising the influence of pest and disease pathogens and allowing for the developing root to be firmly footed in soil moisture. Table 2 shows the results of a seedling survival trial conducted in 1988, and clearly demonstrates the effect of the minimum soil temperature on the rate of development and the survival of cotton seedlings. This trial shows the relationship temperature has on cotton
growth and development and this relationship has not changed in the past 30 years.
|Min soil temperature at 10cm||Seed emerging and survival rate||Days to complete emergence|
Table 2: Effect of temperature on cotton seedling survival and growth rate (Constable and Shaw 1988).
In 2018, CSD laboratory team conducted a study to research the effect of low temperatures on rates of germination. A seven-day germination test was conducted at a range of different temperatures on a single seedlot of cottonseed. Figure 4 clearly illustrates the increased rate of germination with increased temperatures within the tested range. While radicle emergence did occur at lower temperatures germination to a length of 40 mm, which is required for the seedling to be considered germinated under the assessment protocol, did not occur below 18°C. Slow development at establishment in field conditions opens the seedling up to insect and disease attack and expends seed energy reserves. CSD recommends utilising the traffic light tool for planting as a guide to planting time decisions, and to ensure that the cotton seed has the best opportunity to germinate and emerge healthily.
Figure 3: Cotton sensitivity to cold temperature during germination.
Figure 4: Effect of 7 day germination test at a range of constant temperatures on the same AUSlot.
© 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.