Nitrogen Status and Utilization in Rhizosphere of Rice

A greenhouse pot experiment was conducted with hybrid rice (Ocyza Sativa L.) in order to stndy Nstatus and utilization in the rhizosphere of rice. The experiment was composed of three treatments: withoutN, ￣(15)NH_(4-) N and ￣(15) NO_(3-) N. Plant roots were separated from the soil by a nylon cloth, and 1 mm incrementsof soil, moving laterally away from the roots, were taken and analyzed for various N froms. The labelled Nin the plants ranged from 67.51% to 69.24% of the total amount of N absorbed by the rice seedlings withthe labelled fertilizer N treatments. This shows that the N in the plants came mainly from the fertilizers.However, the N absorbed by the rice seedlings accounted for less than 35% of the total amount of the Ndepletion in the soil near the rice roots, indicating an important N loss in the rhizosphere of rice. The soilredox potential (all treatments) and the concentration of the labelled NO_3-N (the labelled NH_(4-_)N treatmentonly) decreased as the distance from the rice roots increased in the rhizosphere of rice. In contrast, theconcentration of the labelled NH_(4-) N increased a.s the distance increased in the same soil zone. These resultssuggested that nitrification occurred in the soil around the rice roots. Therefore, the reason for the N lossin the rhizosphere of rice might be the NO_3 movement into the reductive non-rhizosphere soil (submerged)where denitrification can take place.