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Fate of Fertilizer Nitrogen in the Rice Root Zone¹

ABSTRACT

Poor N use efficiency by rice (Oryza sativa L.) in many regions of the world is due to the intensity of loss mechanisms functioning in the system. A study was conducted to determine the maximum potential loss of fertilizer ¹⁵N in a Crowley (Typic Albaqualfs) silt loam soil where conditions are favorable for both nitrification and denitrification in the root zone of rice. Nitrogen losses were measured in the rhizosphere (soil core with rice plants) and nonrhizosphere (soil core without rice plants) soil systems. The potential N loss in the system with plants was found to be 193 mg N m^–2 d^–1, while N loss due to the rhizosphere effect alone was 143 mg N m^–2 d^–1 (18% of the applied ¹⁵N). About 5% of the applied ¹⁵N was found to be lost due to upward movement of ¹⁵NH⁺₄ into overlying flood-water.

¹ Joint contribution from the Univ. of Florida and Louisiana State Univ. Florida Agricultural Experiment Stations Journal Series no. 6498.

² Professor, Univ. of Florida, Institute of Food and Agricultural Sciences, Central Florida Research and Education Center, Sanford, FL 32771, and Boyd Professor, Center for Wetland Resources, Louisiana State Univ., Baton Rouge, LA 70803.

Received for publication May 10, 1985.