In plants, boron is thought to play a role in cell wall structure, transport of sugars, and retention of reproductive structures. in cotton (Gossypium hirsutum L.), boron is often applied as a foliar spray to correct apparent boron deficiency. The objective of this study was to determine the effects of soil- and foliar-applied boron solutions on yield and boll retention of cotton. In 1991, three genotypes of cotton (DES 119, DES 24-8 ne normal leaf, and DES 24-8 ne okra leaf) were grown on land testing low for soil boron (0.11 µg g^-1 in the top 15 cm). The soil type was a Beulah fine sandy loam and the pH was 7.5. Treatments were soil-applied boron, foliar-applied boron, and the control which received no supplemental boron.

In march 1991, a solution of boron (as Na₂B₈O₁₃ú4H₂O) was sprayed at the rate of 0.89 kg boron ha^-1 (0.8 lb B/A) onto the soil surface of selected plots with a conventional ground sprayer and immediately incorporated. This application increased soil boron concentration to 0.45 µg g^-1. For the foliar-boron plots, four foliar applications at the rate of 0.222 kg boron ha^-1 (0.2 lb B/A), also as Na₂B₈)O₁₃ú4H₂O, were applied. Foliar applications were applied at 10-day intervals beginning just prior to fist bloom and ending at cutout. The total amount of boron applied to foliage equalled that applied to the soil. Foliar solutions were applied to the soil. Foliar solutions were applied over the top with a CO₂ backpack sprayer using a rate of 230 L ha^-1 (24 gpa). During flowering, white flowers were counted three times per week and the total number of flowers produced was calculated. At maturity, open bolls were counted and hand-picked and boll retention percentages were calculated [(boll number/total flowers) x 100].

Foliar application of boron increased leaf boron concentration to 69.8 µg g^-1 compared to that of the control (25.0 µg g^-1). Application of soil boron did not significantly alter leaf boron (28.8 µg g^-1). Nevertheless, the leaf boron concentrations found in the soil treatment and control were slightly above the deficiency level of 20 µg B g^-1. Neither of the boron treatments affected boll retention, number of flowers, or lint yield (which averaged 1290 kg ha^-1 across treatments). There were significant genotype effects on these three traits but there was no significant boron treatment by genotype interactions. DES 119 and DES 24-8 normal leaf exhibited significantly higher lint yields (1380 and 1300 kg ha^-1, respectively) than the DES 24-8 okra leaf (1200 kg ha^-1). DES 119 also exhibited the highest boll retention percentage (66%) followed by DES 24-8 normal leaf (58%) and DES 24-8 okra leaf (40%).

Since the cotton in this study did not respond to soil- or foliar-applied boron (0.89 kg B ha^-1), it appears that soil boron concentrations previously considered "low" (0.11 µg B g^-1) may not necessarily be deficient. However, further tests with applications of higher boron rates are necessary before this hypothesis can be accepted.