Fate of Fertilizer Nitrogen in the Rice Root Zone

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 15 N 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 15 N). About 5% of the applied 15 N was found to be lost due to upward movement of 15 NH + 4 into overlying flood‐water.