Enrico Ceotto

Sustainable Bioenergy Production, Land and Nitrogen Use

In recent years the challenge of reducing the reliance on petroleum and natural gas with the energy produced by agricultural crops has received a renewed interest. However, many scientists have expressed serious reservations about the real benefit of a widespread diffusion of crops grown for energy feedstocks. While a diversification of energy portfolio is strongly needed, one of the greatest scientific challenge for the near future is to identify land use options that minimize negative impact on food prices and greenhouse gases emissions. The objective of this article is to discuss the following topics: (i) competition for land: bioenergy versus food; (ii) bioenergy crops and nitrogen cycling; (iii) plant traits to be targeted for improving land and nitrogen use efficiency; and (iv) the debated role of legumes. Because fertile land, suitable for food production, is a dwindling resource, the production of feedstocks for biofuels should be enhanced by exploiting favourable plant characteristics in marginal land areas. We point out that a rethinking of the concept of marginal land is necessary: not only areas poorly suited to grain crops production owing to low soil fertility, but also land unsuited to produce food owing to food safety reasons. Yet, whether a land area is marginal or not should be evaluated not only from the economic standpoint, but also from the ecological and environmental points of view. Moreover, grain crops residues should be exploited for bioenergy production providing that well devised height of cuttings assure the maintenance of soil organic matter. The main message of this review is that bioenergy should be seen as a complementary product of food and feed production, to be attained by optimized land and nitrogen use. Emphasis is given to the contribution that dedicated perennial lignocellulosic crops might provide in sustainable bioenergy production.

Reduced N supply limits the nitrate content of flue-cured tobacco

Among tobacco components, nitrate is one of the most harmful for human health because during tobacco burning nitrate reacts with alkaloids to form tobacco-specific nitrosamines. Nitrosamines are carcinogenic compounds identified in tobacco products and smoke. Despite a general consensus on the relevance of nitrate on human health, nitrate is currently not considered in the routine analysis of flue-cured tobacco, unlike total alkaloids, reducing sugars, total nitrogen, pesticides and chemicals for sucker control residues. In implementing strategies for tobacco cultivation, it is critical to minimize the nitrate content of the harvested product. On the other hand, the agronomic practices devised to reduce nitrate content should not adversely impact either the yield or commercial characteristics of the product. We carried out a field experiment over three years at one site of the Veneto plane, Northern Italy. We studied the influence of nitrogen supply on productivity and relevant chemical characteristics of flue-cured tobacco. Treatments consisted of four rates of nitrogen supply and one unfertilized control. The rates of nitrogen applied were 0, 15, 30, 45 and 60 kg N ha−1 in 1997, and 0, 20, 40, 60 and 80 kg N ha−1 in both 1998 and 1999. Our results show that annual fertilization rates within 40 kg N ha−1 fulfilled the crops’ requirements for productivity, with no adverse effects on product quality. Higher rates of nitrogen supply resulted in undesired increment in nitrate concentration and reduced sugar content in the cured product, without any gain in productivity. Moreover, we found no correlation between total nitrogen and nitrate concentrations of tobacco cured leaves. Since our data provide evidence that nitrogen content is not a reliable estimator of the harmful nitrate content, we suggest that nitrate should be taken under control in the routine analysis for assessing flue-cured tobacco quality.