A field experiment was carried out on a clayey Dystrophic Red Latosol (Oxisol), under isohyperthermic regime to evaluate the effect of boron application on carrot root yield (Daucus carota) cv. Alvorada. A factorial scheme layout with six treatments (0; 1.7; 3.4; 5.1; 6.8; and 10.2 kg B ha-1) was arranged in a randomized complete block design with three replications. Azomethine-H was used as extractant for boron determination in soil and plant material. The maximum marketable root yield was 50.6 t ha-1, obtained under the estimated concentration of 0.55 mg B kg-1 in the soil. The critical boron (B) concentration in the soil associated with 90% of the maximum marketable root yield was 0.45 mg kg-1. As a first approximate, the levels of B in the soil could be classified as low (<0.30), medium (0.31-0.44), adequate (0.45-0.55) and high (>0.55 mg B kg-1). The B levels in the leaves (on a dry weight basis) were classified accordingly to the following ranges: low (<24.1), medium (2534,9), adequate (3551.9) and high (>51.9 mg kg-1 B).
Daucus carota; oxisol; micronutrient
