Temporal Origin of Nitrogen in the Grain of Tropical Wet-Season Rice

Authors

• J. E. Sheehy, IRRI, DAPO 7777, Metro Manila, Philippines
• M. Mnzava, IRRI, DAPO 7777, Metro Manila, Philippines
• Kenneth G. Cassman, University of Nebraska-LincolnFollow
• P. L. Mitchell, Univ. of Sheffield, Sheffield, UK
• A. B. Ferrer, IRRI, DAPO 7777, Metro Manila, Philippines
• R. P. Robles, Univ. of the Philippines, Los Baños, Philippines
• P. Pablico, IRRI, DAPO 7777, Metro Manila, Philippines

Document Type

Article

Date of this Version

April 2005

Comments

Published in Agron. J. 97:698–704 (2005). Copyright © American Society of Agronomy. Used by permission.

Abstract

The total N in the grain is the integral of the product of the total N absorbed at any instant and the fraction of that N eventually allocated to the grain. We investigated the temporal origin of N in the grain of a wet season rice crop and tested the suitability of ¹⁵N nitrate (NH₄ ¹⁵NO₃) as a label for that purpose. The total N content of rice (Oryza sativa L.) plants was measured by growth analysis throughout the duration of the crop and the measurements were used to calculate the rate of total N uptake. A point-placement technique was used to deliver small amounts of ¹⁵N nitrate to roots of the rice plant and this enabled the eventual fate of the total N absorbed at any time to be determined. The rate at which N was acquired by the panicle exceeded that by the whole plant at 64 d after transplanting (DAT); thereafter, N was transferred from the leaves to the panicle. About 60% of N in the grain was acquired before panicle initiation and was transferred from leaves during grain filling. A comparison between the uptake and retention of labeled nitrate and urea applied separately at 35 DAT showed that 21 and 58% of the ¹⁵N nitrate and ¹⁵N urea, respectively, were recovered. There were no advantages of using ¹⁵N nitrate as opposed to ¹⁵N urea as a label in such research of irrigated rice.