Subdivision of Nitrogen Use Efficiency of Rice Based on 15 N Tracer

Abstract

The nitrogen(N) uptake, and N use efficiencies(NUE) at different rice growth stages(i.e. during basal, tillering and panicle fertilizations) were studied using 15 N isotope tracing. A two-year field experiment with two N rates and two distribution ratios was conducted using two different high-yielding rice cultivars Wuyunjing 23(japonica) and Y-Liangyou 2(hybrid indica). A sub-plot of 15 N isotope tracing experiment with three duplications under the same treatment was also set up in the field. The results revealed that basal nitrogen absorbed by rice was only 1.5%–11.5% before tillering fertilization(eight days after transplanting), 6.6%–24.9% from tillering fertilization to panicle fertilization, and little after panicle fertilization. The overall recovery efficiency of basal N(NUEB) was low and ranged from 9.1% to 22.8%, not significantly affected by different cultivars and N treatments. Tillering fertilizer N was mainly absorbed from tillering fertilization to panicle fertilization, and no longer had effect after panicle fertilization. NUE of tillering N fertilizer(NUET) was 17%–34%, which is almost the same as that of basal fertilizer. NUET of Y-Liangyou 2 was higher than that of Wuyunjing 23. Compared with basal and tillering N fertilizers, NUE of panicle N fertilizer(NUEP) was the highest with a value of 54.0%–82.1%, and Wuyunjing 23 had lower NUE than Y-Liangyou 2. The whole NUE in the entire growth period of all N fertilizers decreased with the increase of N application rate, and varied from 32% to 64%. Among the total N uptake of rice, the contribution was 4.13%–10.59%(average 6.92%) for basal N fertilizer, 3.98%–11.75%(average 7.58%) for tillering fertilizer, 13.32%–37.56%(average 26.02%) for panicle fertilizer, and 45.71%–70.83%(average 59.91%) for the soil. The experiment also revealed that the more the basal and tillering fertilizers applied, the lower the total NUE. It is suggested that rice N management, the N absorption and utilization from fertilizer applied at different stages should be considered to improve the NUE of rice, and ensure the hig yield while avoid the N loss.