Ho Ando, Chikako Mihara, Ken-ichi Kakuda, and Genshichi Wada
Soil Sci.Plant Nutr. 42-3, 531-538 (1996)
Key words: CEC, nitrification, rice plant, topdressed, zeolite
High rice (oriza sativa L.) yields are closely related to plant absorption of a large amount of nitrogen (N). However, there is little information on the fate of N applied at the middle growth stage of rice. Labeled 15N ammonium sulfate was applied at the panicle formation stage in Experiment 1, and 10d after heading in Experiment 2. Zeolite was also added at the concentration of 0, 0.01,and 0.1 kg/kg to increase the cation exchange capacity (CEC) of the soil. The amount of 15N fertilizer in the soil surface water decreased exponentially and the fertilizer disappeared within 2d after application. The soil that received zeolite at 0.1 kg/kg exhibit significantly less 15NH4+-N in the surface water and in the soil solution than the soil without the zeolite amendment. A significantly larger amount of exchangeable 15NH4+N was observed in the high zeolite treatment of soil compared to the low zeolite treatment of soil. The amount of exchangeable 15NH4+-N increased initially, and thereafter, decreased to traces 4d after application in Experiment 1, while 6 or 9d after application in Experiment 2. The disappearance of exchangeable 15NH4+-N could be attributed mainly to the uptake by plants. The zeolite amendment or the time of N application did not significant affect the amount of immobilized N. The rate of N adsorption was inhibited with increasing zeolite application. Moreover, zeolite application did not increase the recovery percentage of ammonium sulfate by rice plant. The total recovery of applied N ranged from 65 ti 75%, irrespective of the zeolite treatments or time of N application.