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Leaf Area Indices and Nitrogen Uptake of Flue-Cured Tobacco as Affected by Plant Density and Nitrogen Rate¹

Effects of three plant densities and two nitrogen rates on leaf areas and nitrogen uptake by tobacco plants were studied during 1961 and 1962. A study was also made on the economics of these treatments.

Leaf area indices (LAI's) for both years increased with time until the reduction in total leaf area through loss of senescent lower leaves became greater than the gain in leaf area of the active upper leaves. The highest maximum LAI of 5 in 1961 was obtained for the high nitrogen rate and the 25-cm spacing. The lowest maximum LAI of 2.5 was obtained for the low nitrogen rate and the 76-cm spacing. LAI's increased with high nitrogen and at both levels of nitrogen the LAI's were in the order of 25 > 51 > 76-cm spacings in 122-cm beds.

Relationships between leaf area and leaf weight per plant were very similar during 1961 and 1962. Correlation coefficients for leaf areas and weights varied from 0.95 to 0.99 in 1961 and from 0.92 to 0.99 in 1962. In both years, better correlation appeared between leaf areas and weights at the high nitrogen rate than at the low nitrogen rate, with spacing treatments having little effect on the relationships.

Nitrogen uptake was much higher with the high nitrogen treatment than with the low nitrogen treatment.

The yield of flue-cured tobacco increased with closer plant spacing and the higher nitrogen rate. However, leaf quality decreased with the high nitrogen rate and offset the higher yields in total dollar value per hectare. The quality of tobacco appeared to be influenced more by the nitrogen application than by the different plant spacings~ The most profitable treatment combination appeared to be the 76-cm spacing at the low nitrogen rate.

Key Words: leaf area • nitrogen • tobacco • plant density

² Soil Scientist, USDA, Florence, S. C., (now Assistant Water Scientist, University of California, Davis) and Soil Scientists, Florence, S. C., (now at Fleming, Ga.); and State College, Miss., respectively.

Received for publication February 13, 1967.