Alessandro Peressotti

Application of biochar on mine tailings: Effects and perspectives for land reclamation

Mine tailings represent a source of toxic pollutants, mainly heavy metals, which may spread to the surrounding areas. Phytostabilization, a long-term and cost-effective rehabilitation strategy, can be achieved by promoting the establishment of vegetation to reduce the risk of pollutant transfer. In this work, the application of pyrolyzed biomass (biochar) was studied to evaluate the amelioration of the mine tailings properties for potential use as a phytostabilization technology. Four substrates were obtained by mixing the mine tailings from a dumping site in Cave del Predil (NE, Italy) with biochar from orchard prune residues at four dosages (0%, 1%, 5% and 10% biochar in the mine tailings). The physical and chemical properties were determined and the bioavailability and leachability of the contaminants were estimated. The pH, the nutrient retention in terms of cation exchange capacity and the water-holding capacity increased as the biochar content increased in the substrates and the bioavailability of Cd, Pb, Tl and Zn of the mine tailings decreased. The changes promoted by the biochar seem to be in favor of its use on mine wastes to help the establishment of a green cover in a phytostabilization process.

More new carbon in the mineral soil of a poplar plantation under Free Air Carbon Enrichment (POPFACE): Cause of increased priming effect?

[1] In order to establish suitability of forest ecosystems for long-term storage of C, it is necessary to characterize the effects of predicted increased atmospheric CO2 levels on the pools and fluxes of C within these systems. Since most C held in terrestrial ecosystems is in the soil, we assessed the influence of Free Air Carbon Enrichment (FACE) treatment on the total soil C content (C-total) and incorporation of litter derived C (C-new) into soil organic matter (SOM) in a fast growing poplar plantation. C-new was estimated by the C3/C4 stable isotope method. C-total contents increased under control and FACE respectively by 12 and 3%, i.e., 484 and 107 gC/m(2), while 704 and 926 gC/m(2) of new carbon was sequestered under control and FACE during the experiment. We conclude that FACE suppressed the increase of C-total and simultaneously increased C-new. We hypothesize that these opposite effects may be caused by a priming effect of the newly incorporated litter, where priming effect is defined as the stimulation of SOM decomposition caused by the addition of labile substrates.

Yield, water use efficiency and nitrogen uptake in potato: influence of drought stress

SummaryA lysimeter experiment was performed to study the optimal allocation of limited water supply in potatoes.Irrigation regimes equal to 40, 60 and 80% of maximum evapotranspiration (ET) were evenly applied over the crop cycle. Other treatments involved withholding 80 mm of irrigation, based on ET, beginning at each of three designated growth stages (tuber initiation, early and late tuber growth). An irrigated control treatment, restoring the entire ET, was included for comparison.Continuous drought stress reduced photosynthesis as irrigation volumes were reduced. Plant biomass and tuber yield decreased almost proportionally to water consumption, so that WUE was roughly constant. N uptake was highest in the control and in 80% ET treatment.Withholding water during tuberisation severely hindered plant physiological processes and penalized tuber yield. Reductions in photosynthesis, total biomass and yield were the greatest when drought was imposed during tuber initiation. The earliest stress resulted in the lowest WUE and N uptake.A new crop water stress index (SI) was proposed, which combines atmospheric demand for water and canopy temperature.

Sampling soil-derived CO2 for analysis of isotopic composition: a comparison of different techniques

A new system for soil respiration measurement [P. Rochette, L.B. Flanagan, E.G. Gregorich. Separating soil respiration into plant and soil components using analyses of the natural abundance of carbon-13. Soil Sci. Soc. Am. J., 63, 1207–1213 (1999).] was modified in order to collect soil-derived CO2 for stable isotope analysis. The aim of this study was to assess the suitability of this modified soil respiration system to determine the isotopic composition (δ13C) of soil CO2 efflux and to measure, at the same time, the soil CO2 efflux rate, with the further advantage of collecting only one air sample. A comparison between different methods of air collection from the soil was carried out in a laboratory experiment. Our system, as well as the other dynamic chamber approach tested, appeared to sample the soil CO2, which is enriched with respect to the soil CO2 efflux, probably because of a mass dependent fractionation during diffusion and because of the atmospheric contribution in the upper soil layer. On the contrary, the static accumulation of CO2 into the chamber headspace allows sampling of δ13C-CO2 of soil CO2 efflux.

Stomatal numbers, leaf and canopy conductance and the control of transpiration

De Boer et al. (1) concluded that doubled atmospheric CO2 concentration ([CO2]), by reducing both leaf stomatal density and conductance, would decrease modeled annual transpiration by approximately 60 W m−2 in Floridas subtropical vegetation. This remarkable result was accompanied by statements that current Floridian annual evapotranspiration (ET) is approximately 120 W m−2 and that transpiration is approximately 50% of current ET (i.e., ∼60 W m−2). (The remainder of ET is accounted for by evaporation from soil and interception water.) Because 60 minus 60 W m−2 equals 0 W m−2, modeled transpiration in subtropical Florida would therefore cease with CO2 doubling, implying …

Nitrogen in drainage water as influenced by soil depth and nitrogen fertilization: a study in lysimeters

Abstract To evaluate the environmental risk associated with nitrogen fertilization of arable crops, the concentration of (NO2 + NO3)-N (Nitr-N) and NH4-N (Amm-N) in leachate, as well as the water volumes drained from cultivated field lysimeters were monitored for three years in Udine (north east Italy). Three crops (barley, soybean and maize) were subjected to three levels of nitrogen fertilization : nil, intermediate (about 125 kg ha−1 year−1) and high (about 250 kg ha−1 year−1). Lysimeters collected leachates at two depths in the soil profile (0.5 and 1.0 m), whose depth was limited by gravel. The concentration of Nitr-N in leachate increased with soil depth and fertilization level from 7.0 mg l−1 (unfertilized soil 0.5 m deep) to 25.3 mg l−1 (highly-fertilized soil 1.0 m deep). Even in the absence of fertilization, there was a significant probability (19 per cent in the 0.5 m deep soil and 57 per cent at 1.0 m deep) of exceeding the current threshold values for NO3-N content in waters (11.3 mg l−1), while the probability was negligible for Amm-N. At the intermediate and high fertilization levels, NO3-N limits were exceeded more frequently (34 and 55 per cent of occasions in the shallow soils, respectively ; 70 and 86 per cent in the deep soils, respectively). The highest values of Nitr-N in leachate were observed between June and July ; however, the peaks of Nitr-N concentration were recorded later in the year in the deep soil than in the shallow one. Nitrogen fertilization and soil depth increased total N losses, but their effect on N concentration of leachate was balanced by a decrease of drainage volumes, which were affected by the evapotranspiration of cultivated crops. Grain yield of unfertilized crops was economically inadequate, but the intermediate fertilization level appeared adequate for satisfactory economic returns. Considerations are also reported on the relationship between efficiency and leaching of N fertilization.

Cropland and Grassland Management

According to the latest National Inventory, the Italian agricultural sector is a source of GHGs with 34.5 Mt of CO2 eq in 2009, corresponding to 7 % of the total emissions (excluding LULUCF). In particular, more than half (19.1 Mt of CO2 eq) are N2O emissions from soils. Although the national methodology is in accordance with Tier 1 and 2 approaches proposed by the IPCC (2006), still empirical emission factors are used to assess the emission from fertilizer (e.g. 0.0125 kg N2O–N kg−1 N from synthetic fertilizers). Disaggregated data at sub-national level, including models and inventory measurement systems required by higher order methods (i.e. Tier 3), are not available in Italy so far and comparisons with the other two approaches cannot be performed at the moment. Despite the large soil organic carbon pool in the agricultural soils and the recent institutionalization of the ‘National Registry for Carbon sinks’ by a Ministerial Decree on 1st April 2008, the last Italian greenhouse gas Inventory did not report CO2 emissions from the agricultural sector. In this context, this chapter wants to summarize the main outcomes coming from the main long-term experiments present in Italy by integrating experimental and modeling approaches, which can provide national emission rates and a solid base to test and calibrate simulation models to estimate greenhouse gases emissions from Italian agricultural soils. What emerges clearly from the analysis is that the agro-ecosystems may sequester large amount of SOC if appropriate management practices are adopted. Moreover, the use of simulation models calibrated at local level and spatially applied, as done for the Carboitaly project, may certainly reduce the uncertainty of these estimations.