Cotton yield and fibre quality are intrinsically linked to boll development and maturity. Boll number and boll weight are the two primary yield components, with a higher number of heavier bolls leading to increased yield. A longer flowering period allows for more squaring nodes, which translates to a higher number of fruiting sites that produce squares and subsequently the number of bolls per metre. However, the cotton plant naturally sheds a significant portion of its of squares as boll load increases approaching cutout.
Why use Boll Counting?
Boll counting is a more reliable indicator of yield potential in a cotton crop than retention percentages because it directly measures the number of bolls, which is the primary determinant of yield. Retention percentages, while useful, only provide information about the proportion of fruiting sites that remain on the plant at a given time and don’t reflect the absolute number of developing bolls. It is conceivable that crops can have low retention and high numbers of bolls resulting in excellent yields.

How to use Boll Counts
Boll counts involve physically counting the number of bolls per unit area, usually a linear metre, in a field (due to varying boll weights).
Boll counts are the best way to provide an idea of the crop’s progress during the important flowering period. Providing there is no stress on the crop boll number production will follow an optimal rate such as that used in CottonTracka.
- A common rule of thumb is that approximately 12-14 bolls per metre translate to 1.0 bale per hectare in irrigated systems, and 15-20 bolls per metre2 equate to 1.0 bale per hectare in rain grown situations.
Accuracy of Boll Counts
Accuracy of boll counts is often limited by in-field variability and sampling techniques. Precision agriculture tools like EM surveys, NDVI and yield maps from previous seasons can help identify representative sampling areas. If a field is variable more counts will be needed.
Boll Weight
While boll number plays a major role, boll weight can also significantly impact yield and fibre quality.
Several factors influence final boll weight and consequently affect yield estimates derived from boll counts.
- Seed Number per Boll: The number of ovules that develop into seeds within a boll is determined during square initiation and significantly impacts boll weight.
- Lint Weight per Seed: The amount of lint produced per seed plays a major role in determining boll weight. This impact will also affect micronaire of the fibre.
- Environmental Conditions: Throughout the season play a critical role in boll development and maturity:
- Temperature: Temperature significantly affects boll development. It affects photosynthesis and respiration which affect the amount of carbon assimilates available for boll growth and it also affects how long a boll grows for. For example, warmer temperatures can sometimes speed up boll maturity which limits the time for bolls to grow bigger.
- Moisture: Adequate moisture is essential for boll development. Moisture stress during boll filling needs to be severe to limit boll weight, as bolls are less sensitive to stress than leaves. Also, in many instances the crop has made allowances for moisture stress by limiting the number of bolls produced so there are more chances for crops to fill their bolls. Timing of the last irrigation is critical. Watering too early or running out of moisture can reduce both yield and fibre quality.
- Nutrition: Adequate nutrition is vital for healthy boll development and fibre quality. Potassium is critical for boll development and fibre quality, even though its demand comes late in the crop’s life cycle. Premature senescence causes reduction in leaf area which can reduce photosynthesis needed to fill bolls.
- Stress: Various stress factors, including insect pressure and disease, can negatively impact boll development as it can also affect leaf area and photosynthesis.
Understanding the relationship between boll weight and boll factors can help growers make informed decisions about yield potential. Boll weight refers to the amount of lint per boll, while boll factors indicate how many bolls/m are needed to produce 1.0 bale/ha. A lower boll factor generally suggests heavier bolls and higher potential yield for a given number of bolls.
Using Boll Counts and Boll Factors
By combining boll counts with boll factors, growers can get a more refined yield estimate. CSD provides data on boll factors for each variety in dryland and irrigated production types. (www.csd.net.au/boll-factors)
- For example, if a variety that has a boll factor of 12 and in-field exhibits 150 bolls per metre, the estimated yield would be approximately 12.5 bales per hectare (150 bolls/12=12.5 b/ha).
It’s crucial to remember that both boll counts and boll factors offer estimates. Actual yield can vary due to factors like in-field variability, boll weight fluctuations, and unforeseen environmental conditions. However, by using these tools in conjunction with other crop monitoring techniques (NAWF), growers can gain valuable insights into yield potential and make more informed management decisions throughout the season. Timing cutout appropriately by tracking NAWF can optimise the period of flowering for your location and situation which can increase boll number and size.
CottonTracka® Can Help
CottonTracka® (https://csd.net.au/trackwithcottontracka/) is a tool developed by CSD to help cotton growers monitor and optimise their crop performance. One of the ways CottonTracka assists with boll counts is by providing a visual representation of the optimal rate of boll accumulation. This allows growers to compare the actual rate of boll accumulation in their fields with the optimal rate and identify potential problems.
Reductions in the boll accumulation rate compared to the expected rate based on accumulated degree days can indicate various problems affecting the crop, such as:
- severe weather events not reflected in degree day calculations
- biotic stresses like insects and diseases
- abiotic stresses such as inadequate or excessive water.
Identifying a suboptimal boll accumulation rate allows for timely interventions to address these issues and recover potential yield loss.
Here are some additional ways CottonTracka helps with supporting insights gained from boll counting.
- It provides predictive insights at critical production stages and assists in assessing climatic and environmental influences.
- It uses advanced prediction models, such as BARRY, to provide real-time yield predictions based on boll counts and other crop measurements.
- It integrates with other tools, such as STEFF, to provide information on first flower timing and crop status, which can be used to make decisions about irrigation and nitrogen applications that can impact boll development.
- The CSD Extension team ensures the most up-to-date growth curve and yield prediction information is collected and that the program is regularly updated with the latest varietal characteristics.
Overall, CottonTracka aims to make boll counting more informative for cotton growers, helping them to make realise their yields across varied systems and environments.