The Behavior of Nitrogen in the Rhizosphere of Rice Plant Using the Rhizobox System

Behavior of N in the rhizosphere of rice (Oryza sativa L.) plant was investigated using a rhizobox system filled with a shirasu soil applied with NH415NO3 or 15NH4NO3. The rhizobox consisted of one 2-mm width center compartment(CC), five 1-mm width compartments, and one bulk compartmen(tBC) on both sides of CC.Rice was sowed and grown in CC. After 6th weeks after clutivation,the soil from each compartment were collected and analyzed for contents and 15N excess% of the soil total-N, water-soluble NO3-N,NH4-N and KCl-extractable NH4-N. The obtained results were summarized as follows: 1) The total-N content of soil decreased in all the compartments except CC compared with that before cultivation,but that of CC did not change. 2) The water-soluble NO3-N content of soil decreased remarkably in all the compartments compared with that before cultivation,and about 79% of applied NO3-N was lost from soil due to denitrification. The NO3-N content of soil slightly increased from BC toward CC. The most of NO3-N were derived from the soil N especially in the CC. 3) The contents of water-soluble NH4-N and KCl-extractable NH4-N decreased from BC toward CC and the ratio of water-soluble NH4-N to KCl-extractable NH4-N are 1:10 in all the compart- ments except CC which water-soluble NH4-N was not detected. 4) Mineralization of soil-N and immobilizaition of fertilizer-N were more actively at CC than in the other compartments.