Nitrogen Dynamics and Fertilizer Use Efficiency in Rice Using the Nitrogen-15 Isotope Techniques

4losses. The values of the % N derived from fertilizer application to the plant were significant differences among different plant parts. The N uptake from the CF applied to rice grain, straw and the roots was also significantly (P<0.05) higher than that from DAOR, but the highest proportion of N uptake by rice was from the soil. At harvest, an average of 6.2 and 13.2% of applied N remained in the soil treated with the CF and DAOR, respectively. Fertilizer use efficiency calculated by the N dilution method tended to be higher for CF than 15 DAOR. A significant amount of N fertilizer (average: 30%) was apparently lost from the soil-plant system through ammonia (NH ) volatilization. Following DAOR application, the pH increased by 1.0 to 1.2 units in the 3 top 5 cm of the soil, resulting in high NH volatilization in the first 2 days of the experiment. The NH 33 volatilization accounted for the decrease in soil ammonium-N (NH -N) content. 4