SSSAJ Journal of Natural Resources and Life Sciences Education
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Published in Soil Sci Soc Am J 18:308-312 (1954)
© 1954 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Factors Affecting the Foliar Absorption of N15 Labeled Urea by Tobacco1

Richard Volk and Clayton McAuliffe2

ABSTRACT

Single leaves of Dixie Bright 101 tobacco plants grown in sand culture in the greenhouse were sprayed with N15 labeled urea. Up to 5 mg. of the 15 mg. of nitrogen applied was absorbed by the leaf within 24 hours, and by 6 hours a portion of this nitrogen had been translocated to every plant part. One-half of the absorbed nitrogen was translocated from the sprayed leaf by 24 hours, chiefly to adjacent leaves, the meristem and root.

The absorption of urea was nearly identical through the upper and lower leaf surfaces. Absorption decreased with increasing vertical leaf position with the exception of the uppermost leaves and irrespective of the leaf area. Leaf maturity had little effect if the relative leaf position was the same. However, very young plants did absorb more nitrogen than more mature plants.

Damaging the epidermal hairs by gentle brushing with a camel's hair brush increased absorption of urea tenfold. Such brushing ruptured the impermeable cutinized layer of the epidermal hairs permitting the urea solution to come into direct contact with the epidermal cell wall.

Absorption of urea over a four hour period was found to be 3 to 10 times greater during the night than during the day. Absorption was also 3 times greater in the morning than in the afternoon. This suggests that internal factors in the leaf which undergo diurnal fluctuations may play an important role in foliar absorption of urea.

The absorption of urea from buffered solutions was a function of both pH and the buffer system used. With phosphate buffer, absorption increased as pH increased from 6 to 8.

Absorption of urea was decreased as the concentration of sucrose in the urea spray solution was increased. A one molar sucrose solution decreased urea absorption by one-half. It is postulated that sucrose may reduce the absorption of urea by competing with urea during process of absorption, by decreasing the rate of diffusion of urea toward the absorption surface, or by inhibiting urease activity.

NOTES

1 Contribution from the Department of Agronomy, North Carolina Agr. Exp. Sta., Raleigh, N. C. Published with approval of the Director as No. 538 of the Journal series. Presented before Division IV, Soil Science Society of America, Dallas, Tex., Nov. 20, 1953. Rec. for publication Jan. 28, 1954. This investigation was supported in part by a grant in aid from the E. I. DuPont de Nemours and Co. The assistance of Mrs. Jeannette Krachenberger with the analysis is gratefully acknowledged.

2 E. G. Moss Fellow and Research Associate Professor, respectively.






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The SCI Journals Agronomy Journal Crop Science
Journal of Natural Resources
and Life Sciences Education		 Vadose Zone Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome
Copyright © 1954 by the Soil Science Society of America.