Fabio Castelli

Biochar from Swine solids and digestate influence nutrient dynamics and carbon dioxide release in soil.

Large amounts of livestock manure solids are expected to become available in the near future due to the development of technologies for the separation of the solid fraction of animal effluents. The charring of manure solids for biochar (BC) production represents an opportunity for recycling organic matter (OM) of high nutrient value. The objectives of this study were to evaluate the suitability of BC from swine solids (SS) to improve soil fertility through nutrient supply and decomposition of the OM incorporated into soil and to verify a possible interaction effect on soil nutrient dynamics between digestate application and soil amendment with BC. We monitored at laboratory scale the soil mineral nitrogen (N) and Olsen phosphorus (P) content, and the cumulative carbon dioxide (CO-C) release in treatments with or without a supply of digestate obtained from a biogas plant. The experiment was performed in laboratory microcosms during a 3-mo incubation period. Compared treatments were soil amendments with SS, BC from SS, wood chip, BC from wood chip, and soil with no amendment, each of them with and without incorporation of digestate (10 treatments in total). Soil N levels were unaffected by BC amendments and only increased temporarily when digestate was applied to soil amended with SS or BC from SS. For the same N content, the BC from SS supplied much more P than the nontreated OM. The amount of cumulative CO-C released from soil with BC with or without digestate did not differ from that in the unamended control soil and was lower than that in the soils with noncharred amendments. Soil amendment with BC from SS does not modify soil N availability, whereas it increases the content of P available for crops and reduces the release of CO-C from digestate applied to soil for agricultural purposes.

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.