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CROP ECOLOGY, PRODUCTION, & MANAGEMENT

Early-Season Plant Nitrate Test for Leaf Yield and Nitrate Concentration of Air-Cured Burley Tobacco

^a USDA-ARS, Grazinglands Research, 7207 W. Cheyenne St., El Reno, OK, 73036 USA
^b USDA-ARS, Western Cotton Research Lab, Phoenix, AZ 85040-8830 USA
^c Dep. of Agronomy, Univ. of Kentucky, Lexington, KY 40546-0091 USA

cmackown{at}grl.ars.usda.gov

Profitable yield and satisfactory leaf quality of burley tobacco (Nicotiana tabacum L.) require proper management of N fertilizer. The level of tissue NO^-₃ in tobacco may be a suitable diagnostic test of crop N sufficiency that could be used for N management decisions. This study determined the suitability of early-season tissue NO^-₃ as a predictor of air-cured leaf yield and NO^-₃ concentration. Burley tobacco was grown in 1991 and 1992 on a well-drained Maury silt loam (fine, mixed, mesic, Typic Paleudalf) and a moderately well-drained Captina silt loam (fine, silty, siliceous, mesic Typic Fragiudult) broadcast fertilized just before transplanting with 0 to 392 kg N ha^-1. Tissue NO^-₃ levels of plants sampled from 3 to 5 wk after transplanting and air-cured leaf yields increased with increasing amounts of fertilizer N. Responses differed depending on location and year. When the results were expressed as the percentage of the maximum within year and location, the relationship of leaf yield to early-season NO^-₃ was described by a single linear equation (y = 51.0 + 0.448x; r² = 0.808, P 0.001). However, to use this equation, it would be necessary to include in each tobacco field evaluated a strip of fertilizer N producing near maximum yield. The NO^-₃ concentration of burley tobacco between 3 and 5 wk after transplanting was suitable for predicting the NO^-₃ concentration of air-cured leaf lamina from the top, middle, and bottom stalk positions, and appeared to be insensitive to year and location effects. Use of plant NO^-₃ concentration, as an early-season diagnostic test to predict N sufficiency and NO^-₃ concentration of cured leaf lamina, appeared to offer promise for better N management of burley tobacco. Such a test during the interval between 3 and 5 wk after transplanting fits well into the normal cultivation practices. However, further research would be needed to calibrate the amount of additional N required to correct N deficits by banding N.