47th TWC, Tob. Work. Conf., 2016, abstr. 03

Evaluation of NCDA boron sufficiency ranges for flue-cured tobacco

JERNIGAN C.(1); HARDY D.H.(1); HICKS K.A.(1); McGINNIS M.S.(1); FISHER L.R.(2); VANN M.C.(2)
(1) North Carolina Department of Agriculture and Consumer Services, Raleigh NC USA; (2) North Carolina State University, Raleigh NC USA

Boron (B) is an essential micronutrient for optimum plant growth of flue-cured tobacco and is required in trace amounts (<1.0 lb B/acre). Since use of premium tobacco fertilizer grades that contain trace amounts of B are not typical in today’s production and flue-cured tobacco is not known to be sensitive to B deficiency, B is often not applied. In recent years however, B deficiency in North Carolina has been visually and analytically identified by sampling the most recently mature leaf (MRML). In 2015, research was initiated at five research stations to reevaluate B plant tissue sufficiency ranges using two plant parts (bud and MRML) and investigate associations with plant calcium levels. To assure adequate B sufficiency in transplants, a 1 ppm B concentration in the float bed water was used at all locations. Soil applied treatments of 0, 0.5, 1.0, 2.0, 5.0, and 10.0 lbs B /acre were initiated soon after base fertilizer (8-2-20) application, approximately 2 to 3 weeks after tranplanting. Three foliar treatments of 0.25 lbs B/acre were scheduled at second cultivation, at layby and “as needed” based on visual symptoms, with the latter not initiated. During the growing season, bi-weekly visual ratings were conducted to identify the occurrence of B deficiency and toxicity symptoms. Tissue samples were collected just prior to the two scheduled- foliar applications and at topping. Plots were harvested by stalk position and cured on-station. Yield was quantified and cured leaf was assigned a USDA grade. Crop value was determined through the combination of cured leaf yield and quality. Boron deficiency was not observed in 2015; however, B toxicity was documented at rates above 2.0 lbs B/acre. (Reprinted with permission)