Maria Teresa Dell'Abate

Humic substances along the profile of two Typic Haploxerert

Abstract In Vertisols, organic matter contributes to soil colour by formation of organo-mineral complexes and affects morphological, physico-chemical, biological and biochemical properties. Turbation may affect the chemical and structural composition of the most stabilised fractions of soil organic matter (SOM), i.e., humic substances (HS). The objectives of this study were to: (1) characterise SOM in two Vertisols (V1 and V2) developed under Mediterranean climate in Italy, using some HS characteristics as indicators of SOM turnover in Vertisols, and (2) explore possible differences related to the pedomorphologic conditions of the area under which two soils have formed. SOM evolution along the soil profile was investigated by applying different techniques to chemically extracted HS. Humification parameters, thermal methods, such as Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG) together with isoelectric focusing (IEF) were used. The results showed a significant difference in the chemical characteristics of SOM in the considered Vertisols. A higher amount of total and humified carbon was found in pedon V2. In particular, the results indicated an accumulation of humified compounds in deeper horizons of V2: this effect is particularly significant since both soils were under the same agricultural management and the same climatic conditions, but were different in physiografic position, slope and colour. The higher amount of not humified SOM in the pedon V1 could explain the differences found in the shape and size of soil structure between the two pedons. The different SOM evolution occurring in the two Vertisols apparently influenced the structure and composition of the HS fraction. Thermal analysis and isoelectric focusing data provided evidence of a different level of stabilisation of HS from the two Vertisols. The HS from pedon V2 have a higher molecular weight structure, which would imply a higher level of SOM stabilisation. Conversely, HS in the pedon V1 appeared to be richer in aliphatic and phenolic structures, which may imply the presence of less stabilised HS fractions. These findings agree well with the different water dynamics occurring in the two sites, which confirmed the influence exerted by water on chemical and structural composition of HS and, consequently, their effect in determining Vertisols colour. In conclusion, thermal and isoelectric focusing characterisation of HS appear to shed some light in understanding the structural complexity of Vertisols. The results obtained in the present study, if confirmed on a larger number of Vertisols, suggest the possibility of using HS as indicators of SOM turnover in relation to pedomorphology, use and management of soils.

Thermal analysis in the evaluation of compost stability: a comparison with humification parameters

Characterization of organic matter of six composts from agroindustrial wastes was carried out by both chemical analysis and thermal analysis in order to assess their level of stability. Degree of humification (DH%) and index of humification (HI) were calculated after extraction, fractionation and analysis of the organic carbon from composts. Differential Scanning Calorimetry (DSC) and thermogravimetry (TG) were simultaneously performed in oxidizing conditions on whole ground composts. Thermoanalitical data resulted to be useful in integrating quantitative information coming from chemical analysis of humified fraction of compost organic matter. Particularly, DSC curves allow to distinguish between well and poor stabilized composts, and information deriving from weight losses, registered by TG curves, permits to individuate a thermoanalytical parameter (R1) that resulted to be well correlated to humification parameters DH% and HI.

Assessment of safety and efficiency of nitrogen organic fertilizers from animal-based protein hydrolysates—a laboratory multidisciplinary approach

BACKGROUND Protein hydrolysates or hydrolysed proteins (HPs) are high-N organic fertilizers allowing the recovery of by-products (leather meal and fluid hydrolysed proteins) otherwise disposed of as polluting wastes, thus enhancing matter and energy conservation in agricultural systems while decreasing potential pollution. Chemical and biological characteristics of HPs of animal origin were analysed in this work to assess their safety, environmental sustainability and agricultural efficacy as fertilizers. Different HPs obtained by thermal, chemical and enzymatic hydrolytic processes were characterized by Fourier transform infrared spectroscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis, and their safety and efficacy were assessed through bioassays, ecotoxicological tests and soil biochemistry analyses. RESULTS HPs can be discriminated according to their origin and hydrolysis system by proteomic and metabolomic methods. Three experimental systems, soil microbiota, yeast and plants, were employed to detect possible negative effects exerted by HPs. The results showed that these compounds do not significantly interfere with metabolomic activity or the reproductive system. CONCLUSION The absence of toxic and genotoxic effects of the hydrolysates prepared by the three hydrolytic processes suggests that they do not negatively affect eukaryotic cells and soil ecosystems and that they can be used in conventional and organic farming as an important nitrogen source derived from otherwise highly polluting by-products.

Nitrogen losses, uptake and abundance of ammonia oxidizers in soil under mineral and organo-mineral fertilization regimes.

BACKGROUND A laboratory incubation experiment and greenhouse studies investigated the impact of organo-mineral (OM) fertilization as an alternative practice to conventional mineral (M) fertilization on nitrogen (N) uptake and losses in perennial ryegrass (Lolium perenne) as well as on soil microbial biomass and ammonia oxidizers. RESULTS While no significant difference in plant productivity and ammonia emissions between treatments could be detected, an increase in soil total N content and an average 17.9% decrease in nitrates leached were observed in OM fertilization compared with M fertilization. The microbial community responded differentially to treatments, suggesting that the organic matter fraction of the OM fertilizer might have influenced N immobilization in the microbial biomass in the short-medium term. Furthermore, nitrate contents in fertilized soils were significantly related to bacterial but not archaeal amoA gene copies, whereas in non-fertilized soils a significant relationship between soil nitrates and archaeal but not bacterial amoA copies was found. CONCLUSION The application of OM fertilizer to soil maintained sufficient productivity and in turn increased N use efficiency and noticeably reduced N losses. Furthermore, in this experiment, ammonia-oxidizing bacteria drove nitrification when an N source was added to the soil, whereas ammonia-oxidizing archaea were responsible for ammonia oxidation in non-fertilized soil.