| Summary: | A field experiment was conducted in Ninghe, Tianjin, China, using the <sup>15</sup>N isotope method to determine the fate of N sources, application effect of organic fertilizer on the growth of rice plant organs, N uptake by rice, and N use efficiency. The experiment included eight treatments: CK-N (control + no-duck), CK-D (control + ducks), CF-N (chemical fertilizer + no-ducks), CF-D (chemical fertilizer + ducks), CM-N (chemical fertilizer + organic fertilizer + no-ducks), CM-D (chemical fertilizer + organic fertilizer + ducks), CD-N (chemical fertilizer 30% off + organic fertilizer + no-ducks), and CD-D (chemical fertilizer 30% off + organic fertilizer + ducks). The results showed that the application of organic fertilizer whether CM or CD in grain and leaf significantly increased N concentration; leaf and root P concentrations over control (CK) and chemical fertilizer (CF). In contrast, straw and root N concentrations, including grain and straw P concentrations did not show any difference between duck and no-duck treatment. Moreover, non-significant differences were found in <sup>15</sup>N fresh grain and husk concentration. Both organs ranged from 14.2⁻14.4 g·kg<sup>−1</sup> and 6.2⁻6.3 g·kg<sup>−1</sup>, respectively. Likewise, N uptake and N use efficiency in fresh grain and husk were not significantly differed within duck and without duck treatment. However, N uptake in fresh grain and husk ranged at the rates of 54.90⁻93.69 and 6.43⁻11.04 kg ha<sup>−1</sup> with duck and without duck treatment. N use efficiency in fresh grain and husk ranged from 21.55%⁻34.61% and 2.61%⁻4.24%, respectively. Overall organic fertilizer has a significant influence on rice growth and promotes crop productivity.
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