Supplemental Boron, Boll Retention Percentage, Ovary Carbohydrates, and Lint Yield in Modern Cotton Genotypes

Cotton (Gossypium hirsutum L.) is sometimes grown on soils with low B concentration. However, most of the literature regarding the effects of supplemental B on cotton was obtained from obsolete, low-yielding genotypes rather than modern, high-yielding genotypes. Therefore, the objective of this study was to determine the effects of soil- and foliarapplied B on leaf blade B concentration, boll retention, and lint yield of modern cotton genotypes. In 1991, three genotypes (DES 119, DES 24-8 ne normal leaf, and DES 24-8 ne okra leaf) and in 1992, two genotypes (Deltapine 20 and Deltapine 5415) of cotton were grown in the field on a Beulah fine sandy loam (coarse-loamy, mixed, thermic Typic Dystrochrepts) having 0.11 mg kg⁻¹ hot water extractable B concentration. Treatments included preplant soil and foliar (first flower to end of bloom) B (78% Na₂BₛO·4H₂O, 20% Na₂B₄O₇·5H₂O) applications for seasonal totals of 0, 0.89, or 1.78 (1992 only) kg B ha⁻¹. The lowest rate of foliar-applied B increased leaf blade B concentration from 25 to 70 mg kg⁻¹ in 1991 and from 54 to 108 mg kg⁻¹ in 1992. In 1992, the highest rate of foliar B applications resulted in a leaf blade concentration of 154 mg B kg⁻¹. Soil-applied B did not alter leaf blade B concentration in 1991, but slightly increased leaf blade B concentration in 1992 from 54 to 71 mg kg⁻¹. Soil B concentrations were higher during the midseason than the preplant period, suggesting that preplant soil B analysis may not accurately foreshadow soil B supply during the season. Soil B or foliar B applications did not affect boll retention percentage, flower number, or lint yield in either year. Supplemental B did not affect boll distribution in 1991, but in 1992, foliar B applications increased the percentage of fruit on monopodial branches. In both years, supplemental B did not greatly affect fiber properties with the exception that supplemental B increased fiber micronaire reading of Deltapine 20 in 1992. The results suggest that modern cultivars may not always need supplemental B when soil B concentration is moderately low.