As the season progresses and crops approach maturity and bolls start to open, one focus shifts to assessing yield potential. Traditionally, boll factors have served as a method for estimating this potential. However, their reliability can be questionable due to the inherent variability across seasons that cause differences in the responses between boll size and boll numbers with yield. Variability can also stem from factors such as field inconsistency, sampling representativeness with boll counts and fluctuations in boll weights up and down the plant.
The Role of Boll Factors
At their core, boll factors offer insights into the comparative weights of bolls across different varieties. Assuming all other conditions are relatively constant, a variety sporting a lower boll factor is expected to outyield one with a higher factor, given identical boll counts. It’s important to note that regional, seasonal, and stress-related factors can significantly influence boll factors. For instance, adverse weather conditions can lead to increased shedding of squares and bolls, potentially altering growth patterns and resulting in a higher count of smaller, late-set bolls. This, in turn, increases the number of bolls needed to produce a bale.
Understanding Boll Weight Variability
Boll weight is determined by the growth conditions from the initiation of the square to its maturity. Factors such as the number of seeds per boll, which can range from 30-35 in healthy crops, play a crucial role. The period from square initiation to flowering, typically 3-4 weeks, is critical and sensitive to environmental stress, including temperature and moisture. Genetics, crop stress, and nutrition significantly influence the number of ovules, which are further impacted by environmental conditions like nighttime temperatures. This season, nighttime temperatures exceeding 25°C in January could adversely affect ovule fertilisation.
Exploring Alternatives
Acknowledging the limitations of boll factors, CSD and CSIRO have introduced BARRY, a standalone yield prediction model that allows crop managers to input crucial growth stage metrics to evaluate yield potential. For an integrated experience use CottonTracka which incorporates BARRY and facilitates real-time visualisation and tracking of boll counts from flowering through to defoliation and offers yield prediction at Cutout and End of Season.
For more information on a demonstration of the benefits CottonTracka can have on your cotton crop management, please get in contact with your local CSD Extension Team member.
* For either method, ensure field data is representative. A boll factor update will be made available on our website soon.
Chris Teague
CSD Digital & Data Manager