CORESTA Meeting, Agronomy/Phytopathology, 2021, Online, AP 04

Experiences in evaluation of boron needs in North Carolina flue-cured tobacco production: a summary of plant tissue sufficiency data and impacts on yield and quality

HARDY D.(1); VANN M.C.(2); JERNIGAN C.(3); McGINNIS M.(1); HICKS K.(1)
(1) Agronomic Division, North Carolina Dept. of Agriculture and Consumer Services, NC, U.S.A.; (2) Crop and Soil Science Department, North Carolina State University, NC, U.S.A.; (3) Helena Chemical Co., U.S.A.

Boron (B), an essential micronutrient for optimum plant growth, is required in trace amounts (<1.1 kg B ha-1) by flue-cured tobacco. In past decades, boron deficiency in North Carolina has not been prevalent. However, recently, its deficiency has been visually and analytically identified to warrant investigation. From 2015-2018, field research was conducted at fourteen locations to evaluate boron plant sufficiency ranges and its application on yield, quality, and leaf chemistry of flue-cured tobacco. Soil-applied rates were 0, 0.6, 1.1, 2.2, 5.6, and 11.2 kg B ha-1. Foliar treatments were evaluated at total rates of 0.6 or 1.1 kg B ha-1 applied in combination as singular (at layby) and split treatments (at second cultivation and layby) or as needed based on visual symptoms. Treatments were arranged in a randomized complete block design with four replications. Tissue samples were collected at 3 growth stages: 1) early at 3 weeks after transplanting (WAT) - bud and most recently mature leaf (MRML), 2) midseason at 7 WAT - bud and MRML, and 3) at topping - MRML. Yield, quality, value, and leaf chemistry were evaluated. Deficiency was not visually observed at any site even when tissue concentrations were as low as 11 mg kg-1 (sufficiency range, 18 to 75 mg kg-1). Toxicity was observed and analytically verified at rather low rates of application. Boron application affected yield in one of the three years: 2015 - 17 % increase at one location and 27 % to 30 % decrease at one location. The bud or MRML may be used to evaluate boron plant status, but sampling 3 WAT may be too early. If boron concerns exist, soil-applied application up to 1.1 kg ha-1 or foliar applications up to 0.6 kg ha-1 appear safe. Our findings do not support the need for routine boron application to flue-cured tobacco in North Carolina.