Boll Shedding and Boll Load in Nitrogen‐Stressed Cotton

AbstractBoll shedding in cotton is thought to depend on the crop growth rate and the demand for plant assimilates by the growing bolls. This study was designed to test the hypothesis that the ratio of boll load (BOLL) and carrying capacity (CA), defined as the maximum boll load, could be used to index the boll shedding fraction for cotton plants with different crop growth rates. Cotton was grown in a greenhouse in 1987 and 1988 with 0, 18, 36, 72, and 144 mmol of N applied at 2‐wk intervals. In 1987, maximum leaf area index (LAI) for the five treatments ranged from 0.6 to 2.2 and maximum BOLL from 5.3 to 23.1 bolls m−2. In 1988, maximum LAI ranged from 1.2 to 4.2 and maximum BOLL from 9.1 to 39.5 bolls m−2. In both years boll sizes for the highest N treatment averaged 4.1 g seed cotton boll−1. Average boll sizes declined for treatments receiving less N, but only the 0 N‐treatment boll sizes were less than 80% of the 144 mmol N treatment. Boll shedding fractions depended on treatments and BOLL. However, for both years boll shedding fractions were highly correlated with the ratio BOLL/CA (R2 = 0.84). Assuming a 1:1 line, the standard error of estimate (SE) was 0.13. Values of CA were highly correlated with maximum LAI (R2 = 0.98) suggesting that the primary effect of N deficits was reduced light interception because of smaller LAI. This analysis suggests, therefore, that the ratio BOLL/CA can be used to index boll shedding fraction in cotton and, with some estimate of CA based on expected yields or LAI, may have value as an input for cotton crop management.