**1. Introduction**

166 Management of Organic Waste

Wiley, J.B. & Assadi B. (2002) Redevelopment Potential of Landfills: A Case Study of Six

Waste/ Recycling Conference, Lake George, NY

New Jersey Projects, Federation of New York Solid Waste Associations Solid

Driven by climate change and population growth, increasing human pressure on land forces conversion of natural landscapes to agricultural fields and pastures while simultaneously depleting land currently under agricultural use (Lal, 2009). Consequently, a vicious circle develops; further aggravating climate change, soil degradation, erosion, loss of soil organic matter (SOM) and leaching of nutrients. Therefore, sustainable concepts for increased food production are urgently needed to lower pressure on soils, in order to reduce or prevent the negative environmental impacts of intensive agriculture. A key for such strategies is the maintenance or increase of SOM level inducing positive ecosystem services such as increased productivity, nutrient and water storage, intact filter capacity, rooting, aeration and habitat for soil organism etc. (Fig. 1). In summary, SOM improves soil fertility and C storage (C Sequestration).

Fig. 1 Soil quality is a function (f) of available water holding capacity (AWC), soil organic matter level (SOM), root density (Rd), cation exchange capacity (CEC), clay content (clay) and time (t). The most important factor is SOM as it improves other variables such as AWC, Rd and CEC.

One efficient way to increase SOM level is compost application, produced especially from biomass wastes. During the last decades, attention was paid at the professionalization of composting due to several trends in today's society: On the one hand, growth of livestock breeding and intensication of crop production has occurred while an increasing shortage of

<sup>\*</sup> Corresponding Author

Synergisms between Compost and Biochar for Sustainable Soil Amelioration 169

Fig. 2. Different stages during composting as function of time, appearance and succession of compost biota, temperature and further processes (based on Lechner et al., 2005 and Smith

During the mesophilic phase, labile C-rich substrates are rapidly metabolized by a mixture of bacteria, actinomycetes and fungi preferring moderate temperature typically between 15 and 40 °C. Due to this aerobic metabolism, heat is generated. Turning the material leading to aeration temporarily decreases temperature, resulting in a rapid decomposition of further available material and thus, temperature increases again (Fig. 2). During the termophilic phase, temperature rises above 40 °C, favouring mainly actinomycetes and thermophilic bacteria such as *Bacillus*. When labile C compounds of the feed substrates decline, a gradual decrease in temperature occurs leading to the cooling phase (Fig. 2). Especially fungi have a preference for the remaining and more complex and thus degradation-resistant lignin and cellulose compounds. In addition, actinomycetes have a major importance when humic materials are formed from decomposition and condensation reactions Smith & Collins, 2007). The final maturing phase is characterized by even lower temperature below 25 °C and reduced oxygen uptake rates of aerobic microorganisms. During this stage, degradation of the more refractory organic compounds continues and soil meso and macro fauna enters. Organisms of this stage have beneficial influence on compost maturation as well as plant diseases suppression as they are able to metabolize phytotoxic compounds (Gottschall, 1984; Haug, 1993). Thus, compost quality increases especially during the last phase. Compared to the starting feed mixture, the final compost is attributed by a lower C/N ratio of 15 – 20 and

& Collins, 2007).

resources, i.e. fossil fuels, fossil nutrients stocks and arable land, can be recognized. On the other hand, urbanization and growing population interconnected with an increased amount of waste output is responsible for environmental hazards and pollution. Therefore, composting became an efficient means of waste processing, soil amelioration and general environmental improvement.

However, up to now reported C sequestration potential due to compost management is limited in terms of C use efficiency and long-term C preservation even combined with organic farming and no till management. Therefore, new concepts for C sequestration combating against further raise of atmospheric CO2 emissions are urgently needed. One promising option is using the "*terra preta* concept" combining biochar and composting technologies. This concept could enhance quality and material properties of compost products leading to a higher added value and to a much better C sequestration potential due to the long-term stability of biochar.

We hypothesize that composting of biochar together with other biogenous materials containing labile organic matter and nutrients can be an appropriate tool to produce a substrate with similar properties as *terra preta* such as enhanced soil fertility and C sequestration. Current available literature will be reviewed on these aspects.
