The secondBHSS Conference with international participation and held on 17-19 September, 2003 in Borovetz, Sofia region. More than 75 participants from several countries (Austria, Belgium, Bulgaria, Greece, FYRMacedonia, the Netherlands and Russia) took part and presented 52 papers, published in the Journal of Ecological Science – Ecology and Future, 2003.
Detailed review on ‘Tendencies and Perspectives of the Research on Humic Substances – World achievements and research in Bulgaria’was published in the Journal (Krastanov et al., 2003). Additionally, comprehensive discussions on the problems of soil OM have been performed in the Working Group on OM (WGOM) at the EC. According to the already mentioned problems, the main tasks in the field of the soil OM study can be expressed as follows:
1. Assessment of the state of the organic carbon in the soils of the enlarged EU;
2. Highlight the multiple roles of OM in the soil;
3. Get a better insight in the processes resulting in OM depletion;
Formulate good management practices related to OM in the context of its multiple functions;
Recommend actions for areas where soil degradation is a risk;
Contribute to monitoring in the context of action;
Promote to research gaps and requirements in the field of OM.
Each one of these topics is rather broad, covering different aspects of OM fundamental, ecological, and agronomical research. On the basis of these tasks and on the world achievement in research of soil OM we try to appreciate its status in Bulgaria.
The brief overview on the fundamental research in Bulgaria shows up the theoretical model of the linkage of clay minerals and strongly bound components in the structural motive of soil adsorbent and humus stability (Raytchev, 1996; 2000; Raytchev et al., 2004, 2005a, 2005b, 2012).
A number of agronomical researches on long termexperimentsin Bulgaria have provided the most favourable conditions for humification of plant residues ensured by minimum and moldboard tillage (Stoinev, Dimitrov, 1998). The effect of these systems of tillage can increase remarkably if combined with intensive recycling of plant residues. Application of mineral and organo-mineral amendments (natural and modified zeolites, composts) has resulted in humus system stabilization and has allowed managing the humus formation processes and carbon sequestration in soils (Filcheva et al., 1998a).
Ecological studies werefocusedon the soil OM’s role as substance, for blocking or transferring soil pollutants. An important accent was set on the OM solubility and eutrophication role in water basins as well as the erosion impacts the carbon pools and their redistribution in the terrestrial ecosystems.
The role of Fe(OH)3 in creation of organo-mineral formations in the presence of unconventional ameliorants (coal dust, lime materials, etc.) in acidic and sodium saline soils was emphasized. These conditions were favourable for catalyzing of flocculation processes, which leaded to formation of ‘sandwich’ charged colloids. Including Cu+2 in these formations has decreased their toxic effect. Stabilizing of Nan[Fe(OH)] in sodium saline soils and including of Na in organo-mineral formations has blocked Na+ ions inside the soil and has protected leaching of water soluble salts (Raychev, 1996; 2000; Raytchev et al., 2012).
During the Conference the effect of inadmissible practice of stubble burning in Bulgaria has been discussed. The presented results convinced the audience that straw is not a trash, but a valuable product that has to be incorporated into the soil and that the stubbles are potential source of nutrients and energy. They all support and manage biodiversity, and offer possibilities to improve soil fertility.Burning the stubbles results in decrease of soil OM in the humus horizon and it is well known that formation of humus needs a hundred of years. Additionally, burning the stubbles has the following negative effects on the environment: damage soil physical properties and make vulnerable soil surface to soil erosion; provoke health problems, especially for people with respiratory diseases, reduce visibility and increase the risk for transport accident, increase transboundary pollution and greenhouse gas emissions.
Economical effect of plant residues utilization is: reduction of fertilizers application and the most important is soil preservation as Resource of future (Filcheva et al., 2005b). In the last two decades scientists have paid special attention to the study of soil OM status after forest fires (Velizarova, Filcheva, 2001; Bogdanov et al., 2003; Velizarova et al., 2003, 2011, 2014).