Effect of nitrogen application rate and base and topdressing ratio on nitrogen utilization of flue-cured tobacco

ObjectivesThe objective of the study was to clarify the responses of flue-cured tobacco to nitrogen application rates and the basal-topdressing ratio, and fertilizer nitrogen residue and loss, so as to propose an costeffective and environmental-friend nitrogen fertilization method.

MethodsA field experiment using the ¹⁵Ntracer technique was conducted with two N application rates (90 and 60 kg/hm²) and two basal-topdressing ratios (70%:30% and 30%:70%). The basal application was done with ridging and topdressing at 30 days after transplanting. Plant samples were collected at the root elongation, squaring and mature stage of flue-cured tobacco, soil samples in 0-20 and 20-40 cm depth were collected at the mature stage. The N contents and the abundences of ¹⁵N were measured, the yield and output value were investigated after the harvest.

ResultsWhen the nitrogen application rate was reduced from 90 to 60 kg/hm², the absorbed N from basal and topdressing N fertilizer and from soil nitrogen were all decreased; the proportion contributed by fertilizer in the total nitrogen uptake was decreased from 32.1% to 28.1%, whereas that from soil nitrogen was increased from 67.9% to 71.9%; the residues and losses of basal and topdressing fertilizer nitrogen were all decreased with the loss ratio of fertilizer N by 26.9%, and the fertilizer N use efficiency increased by 11.3%. When the proportion of topdressing nitrogen was increased from 30% to 70%, the N uptake ratio from basal application decreased from 15.1% to 9.6%, the loss ratio decreased by 52.9%, and the nitrogen use efficiency increased by 21.7%; while the N uptake ratio from topdressing was increased from 12.7% to 22.8%, the residual ratio increased by 20.5%, and the nitrogen use efficiency decreased by 20.4%; the total contribution rate of fertilizer N was increased from 27.8% to 32.4%, the residual ratio increased by 19.9%, the loss ratio decreased by 49.7%, and the nitrogen use efficiency increased by 20.6% as a result. Neither reducing nitrogen rate nor increasing topdressing nitrogen ratio had significant effect on yield and output value of flue-cured tobacco.

ConclusionsReducing nitrogen application rate and increasing topdressing nitrogen ratio could decrease the loss of fertilizer nitrogen and increase the fertilizer nitrogen use efficiency. Under the experimental condition, the nitrogen application rate of 60 kg/hm² with 70% top dressing was the optimal nitrogen application strategy taking account of ecological benefit and economic benefit.