Influence of different preceding crops on nitrogen fertilizer effect of flue-cured tobacco

In order to rationally choose the preceding crops of rotated flue-cured tobacco,the influence of different preceding crops on the availability of nitrogen fertilizer to flue-cured tobacco was studied by isotope 15N trace technique in a field plot and micro-plot experiment.The results showed that applying nitrogen fertilizer decreased the total sugar content but increased the nicotine content in the leaves at the middle and lower parts of tobacco plant,showing a harmonizing role on the sugar/nicotine ratio.The residual fertilizer nitrogen in soil varied with preceding crops,resulting in different biomass of flue-cured tobacco.Under the conditions of no nitrogen fertilizer application,the effects of preceding crops on the biomass of flue-cured tobacco were in the order of Hordeum vulgareAllium cepaPisum sativumBrassica napus.Preceding crop,nitrogen application rate,and their interaction significantly affected nitrogen fertilizer utilization efficiency(P0.01),and affected the economic traits of tobacco,such as the proportion of upper grade leaves,yield,and production value.It was indicated that Hordeum vulgare and Pisum sativum were the better preceding crops of rotated flue-cured tobacco.