Improving the sustainability of tobacco cultivation by optimizing nitrogen fertilization

Tobacco covers over 4.3 million hectares of agricultural lands in the world and, as other crops, must be grown following sustainability principles. Tobacco Burley type is fertilized worldwide with rates of nitrogen that can be reduced without significant impact on product yield and quality. In this experiment, Burley tobacco (Nicotiana tabacum L.) plants were grown in the field with or without irrigation and fertilized with 0, 120, 240 or 360 kg N ha−1 over two growing seasons. The experimental design was a split-plot, with irrigation treatments in the main plots and doses of N in the sub-plots, with three replications. The elemental plot area was 100 m (10 x 10 m) in both years. The objective was to address N needs based on critical concentrations of N (Nct) and Nitrogen Nutrition Index (NNI), both of which are not available for this crop. Plant dry matter and leaf area were measured during the crop cycle. Specific leaf weight, total N, Nct and NNI were determined. Nct ranged between 2.2 and 4.0% in 2 years. NNI was greater under non-irrigated than irrigated conditions in both years and they generally increased significantly with N fertilization up to 240 kg N ha-1. NNI measured during the rapid growth was positively correlated with yield under irrigated conditions (r = 0.656*). Based on our results, when water is not limiting, the NNI measured at early growth stages could give a useful indication of the effectiveness of fertilization, i.e. the higher the NNI will be in this phase the better will be the response in terms of cured leaves production.