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Using Early-Season Leaf Traits to Predict Nitrogen Sufficiency of Burley Tobacco

USDA-ARS, Grazinglands Research, 7207 W. Cheyenne St., El Reno, OK, 73036
Dep. of Agronomy, Univ. of Kentucky, Lexington, KY 40546-0091

^* Corresponding author (cmackown{at}grl.ars.usda.gov).

Burley tobacco (Nicotiana tabacum L.) requires large amounts of fertilizer N to produce high yields of good-quality air-cured leaf. On well-rained soils, fertilizer N typically is applied as much as 4 wk before transplanting. This results in a delay of up to 9 wk before the onset of rapid growth and N accumulation at about 5 wk after transplanting. Abundant rainfall often occurs during this period and creates the potential for losses of soil and fertilizer N. An early-season N-sufficiency tissue test could guide the tobacco grower in adjusting fertilizer needs of the crop before the last cultivation, which normally occurs about 5 wk after transplanting. The objective of this study was to determine relationships among selected N-nutrition-related leaf traits of tobacco measured 3, 4, and 5 wk after transplanting and to determine if these traits are related to yields of air-cured leaf. Burley tobacco was grown in 1993 at two locations, with 0 to 336 kg N ha^–1 applied before transplanting. One site had a well-drained soil; the other site, moderately well-drained. Total N, extracted chlorophyll, and chlorophyll meter readings were measured on leaf lamina disks taken from lower leaves. Leaf yields at both sites were equivalent at 336 kg N ha^–1, with increases in yield due to added N being less for the well-drained soil. The response patterns of the leaf traits to fertilizer N were different for the two soil types and corresponded to the respective yield response patterns for each site. Neither extracted chlorophyll (335–760 mg m^–2) nor chlorophyll meter readings (23.0–42.6 SPAD units) plateaued with increasing total N of leaf disks (3.50–6.26 g m^–1, 41.2-66.6 mg g^–1 dry wt.). Models for linear relationships among leaf traits were significant (R² = 0.60–0.66; P < 0.001). A 20% increase in relative yield corresponded to about a 25% increase in concentrations of total N and extracted chlorophyll, but only a 5% increase in chlorophyll meter readings. After more testing and calibration with comparisons to a high-N-fertility reference strip, these early-season leaf tissue traits may prove useful in predicting sidedress fertilizer N requirements.

Received for publication November 25, 1996.

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