Research program
Evolution, Stability and Dynamic of Soil Organic Components for a Genetic and Functional Definition
University Co-ordinator
Università degli Studi di PALERMO -
AGRONOMIA AMBIENTALE E TERRITORIALE - PALERMO(PA)
Research Unit Leader
Carmelo DAZZI
Description
Vertisols are particular soil types that have focused the attention of many researchers. Several names have been used in different countries to name Vertisols: black earths, gilgay soils (Australia); black cotton soils (USA); argiles noires tropicales (Zaire); pelosol (Germany); margalitic soils (Indonesia); tirs (Morocco); barros (Portugal); grumusols (Brazil, Indonesia, USA); regurs (India, URSS); terre nere mediterranee (Italy, Francia); tropical black clays; black cracking clays.Such soils typically develop under a soil regime with seasonal moisture deficiencies that are more or less marked. They occur mainly on tropical and subtropical latitudes and are characterized by an univocal combination of properties: a generally high content of clay, mainly montmorillonite; wide and deep cracks in dry seasons; slikensides, micro-reliefs and prismatic aggregates meaning soil movement. Because of they look "to digest themselves", Vertisols seem to be very homogeneous in their physical, chemical and hydrological features. This uniformity, really, is only apparent as was emphasized by some worldwide recent soil surveys concerning the age and the organic matter dynamics in Vertisols from Texas (Kovda et al., 2001) and from Sicily (Dell'Abate et al., 2002). The aim of this research is to use data from SOM dynamics and dating of benchmark Vertisols to provide an interpretation tools of their pedogenetic processes. In cooperation with other research teams (RT), similar keys will be used to define the pedogenetic process of other benchmark soils of our Country (alpine Podzols, Cambisols of the Po river valley, Red Earth in Apulia). To do this, RT of Palermo, together with the other RT of the project, will use chemical-physical and biochemical parameters and radiometric techniques to study the SOM dynamics along soil profiles. In particular, the research activity of Palermo RT will be planned in three steps:1st step) from the 1st month and for 9 months.During this phase, benchmark Vertisols will be selected in representative areas, in collaboration with the other RTs. Such areas will be selected both inside agrarian and forest ecosystems, since the latter have particular influence on SOM dynamics. For their location, national soil maps will be used. In each area, soil profiles will be opened, described in field and sampled according to (i) the polygons method (Williams et al., 1996), (ii) the sequence of genetic horizons and (iii) in relation to their lateral variability produced by soil movements. To survey and to describe their bi- and three-dimensional variability, very large soil profiles will be opened. Expected partial results:- field characterization of the selected soil profiles;- setting up an appropriate scheme of Vertisols sampling to survey also their lateral variability;- soil sampling for lab analyses both with conventional techniques and with the polygons method;Soil survey methodologies and methods of lab analyses will be discussed and selected in agreement with the other RTs. In any case, soil samples will be analysed for the following parameters: 1. pH in H2O and in CaCl2;2. particle size distribution;3. total carbonates;4. organic carbon;5. total carbon;6. total nitrogen;7. cation exchange capacity.;8. microbial biomass carbon;9. Basal respiration (soil CO2 respired to standard conditions of soil temperature and water content); 10. Fractionation of humic substances;11. 13C of SOM;12. 14C dating of humic substances.The analyses from n. 8 to n. 12 will be performed in collaboration with the other RTs.An important aspect of the research concerns the use of carbon stable isotopes to study SOM. Carbon has two stable isotopes of which 12C is the most abundant (~98,9%); the other one, 13C represents ~ the 1,1%. The isotopic abundance of an element is express with the notation δ in ‰, as deviation of the isotopic ratio of the sample from an assumed standard (Craig, 1957), that is generally the Pee Dee Belemnite (PDB): δ (‰) = (Rc-Rst)/Rst x 1000where R is the isotopic ratio (13C/12C) of the sample or of the standard.The biogenic carbon from SOM, have a more negative δ13C than δ13C of atmospheric CO2, because the photosynthesis brings to a sensitive enrichment in 12C of organic matter produced. During this process, plants absorb prevalently more atmospheric 12CO2 than atmospheric 13CO2, diminishing the δ13C of organic matter produced from -8‰ (typical value of atmospheric CO2) to about -27‰ (Longinelli and Deganello, 1999). Therefore, carbon isotopic composition of SOM depends on carbon isotopic composition of organic matter produced from plants, but also depends on processes to which it be subjected (Boutton, 1991).Such processes, biologically mediate, bring to a sensitive increase of the 13C of SOM. 2nd step) from the 6st month and for 12 months.In this step, to compare reliability and repeatability of standardized analysis, an inter-laboratory analytical control will be performed among the RTs by ring-test. Expected partial results:- results of laboratory analyses;- validation of laboratory methodologies employed.Subsequently, an approximate evaluation of soil characteristics will be carried out for a first taxonomic indication and chemical (SOM, carbon/nitrogen ratio, humification parameters: degree, rate and index of humification), and biological and microbiological indicators (metabolic quotient, C biomass/C organic) and them comparison with δ 13C organic results, will be used for the interpretation of SOM dynamics. 3rd step) from 15th month and for 9 months.During this step, statistic elaboration of the data will be carried out to find possible correlations among the different sets of indicators. Moreover, we will aspect some suggestions on the use of the indicators in the evaluations of environmental sustainability.Moreover actions will be addressed:- to find correlations among the parameters investigated by each RT;- to evaluate the degree of sustainability of Vertisols of different ecosystems, to suggest best agronomic practices not only in relationship to present crops but also considering the soils characteristics;- to suggest new ways to classify Vertisols through selected indicators in relationship to the international more used soil classification systems (Soil Taxonomy, World Reference Base);Intermediate objectives:1. identification of benchmark soils to investigate, with characterization of the most meaningful horizons as regards SOM dynamics, through quali-quantitative budgets of organic components and humified substances; 2. ring-test among each RT to validate the accuracy and analytical precision of the laboratory methods in determining some key-indicators valid for the surveyed soils (es. Corg);3. chemical, biological and microbiological characterization of investigated soils by estimated key-indicators from soil samples horizons;4. dating of soils sampled according to traditional and not traditional (method of the polygons) methods; 5. statistic elaboration of the data searching the existing correlations among the different sets of indicators; 6. identification of key-indicators for the evaluation of soil environmental sustainability with different agronomic potentiality; 7. evaluation of new indicators for soil classifications, together with traditional diagnostic parameters; 8. suggestion of a new genetic model for Vertisols.Final objectives:To evaluate SOM dynamics and its implications on genetic models, on taxonomic aspects, but above all on the agronomic management of the Vertisols in xeric environments.
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