To investigate the nitrogen absorption and utilization patterns of sunflower under different levels of nitrogen application in saline farmland

a field micro-area experiment was conducted using

15

N isotope tracing technique

and three levels of nitrogen application (N1=150 kg/hm

2

N2=225 kg/hm

2

N3=300 kg/hm

2

) were designed with no nitrogen application treatment (N0) as the control. The

15

N isotope abundance and total nitrogen (TN) content of sunflower and 0-100 cm soil layer were measured at maturity of sunflower to study the fate and utiliz

ation mechanism of fertilizer nitrogen in each treatment. The results showed that the nitrogen absorption of sunflower increased with the increasing of nitrogen application

and the nitrogen uptake of the sunflower at maturity increased significantly by 38.7% at the N2 level compared with no nitrogen application. The contribution of soil N and fertilizer N to the nitrogen uptake of the sunflower in the current season was 84.9% and 15.1%

respectively. At the N2 level

the contribution ratio of fertilizer N increased by 35.7% compared with N1

and the contribution ratio of soil N decreased by 4.3% compared with N1. The residual fertilizer N decreased with the increasing of soil depth

and 47.4% of residual fertilizer N in the soil mainly concentrated in the 0-20 cm soil layer. At different N application levels

the fate of fertilizer N showed loss rate

>

residual rate

>

utilization rate

and under the nitrogen application level of N2

N utilization rate significantly increased by 22.7% and 14.6% compared with N1 and N3

respectively

and the soil residual rate reduced by 8.5% and 8.6% compared with N1 and N3

respectively. Considering the nitrogen uptake and utilization of sunflower and the nitrogen residue in soil

under 225 kg/hm

2

of nitrogen application

the nitrogen utilization rate was 27.4%

the nitrogen residue rate was 32.3% and the nitrogen loss rate was 40.3%

which was a more suitable nitrogen application rate for moderately salinized farmland.