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

Abstract

AbstractBurley tobacco (Nicotiana tabacum L.) requires large amounts of fertilizer N to produce high yields of good‐quality air‐cured leaf. On well‐drained 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.