SUPPLEMENTAL BORON, BELL 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 o f supplemental B on cotton was obtained from obsolete, low-yielding ge notypes rather than modern, high-yielding genotypes. Therefore, the ob jective of this study was to determine the effects of soil- and foliar -applied B on leaf blade B concentration, bell retention, and lint yie ld 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 genot ypes (Deltapine 20 and Deltapine 5415) of cotton were grown in the fie ld on a Beulah fine sandy loam (coarse-loamy, mixed, thermic Typic Dys trochrepts) having 0.11 mg kg(-1) hot water extractable B concentratio n. Treatments included preplant soil and foliar (first flower to end o f bloom) B (78% Na2B8O13.4H(2)O, 20% Na2B4O7.5H(2)O) applications for seasonal totals of 0, 0.89, or 1.78 (1992 only) kg B ha(-1). The lowes t rate of foliar-applied B increased leaf blade B concentration from 2 5 to 70 mg kg(-1) in 1991 and from 54 to 108 mg kg(-1) in 1992. In 199 2, 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 bl ade B concentration in 1991, but slightly increased leaf blade B conce ntration in 1992 from 54 to 71 mg kg(-1). Soil B concentrations were h igher during the midseason than the preplant period, suggesting that p replant soil B analysis may not accurately foreshadow soil B supply du ring the season. Soil B or foliar B applications did not affect bell r etention percentage, flower number, or lint yield in either year. Supp lemental B did not affect bell distribution in 1991, but in 1992, foli ar B applications increased the percentage of fruit on monopodial bran ches. In both years, supplemental B did not greatly affect fiber prope rties with the exception that supplemental B increased fiber micronair e reading of Deltapine 20 in 1992. The results suggest that modern cul tivars may not always need supplemental B when soil B concentration is moderately low.