**3.7 The role of soil organisms**

182 Management of Organic Waste

Table 6. Potential C sequestration with biochar in soils of the world. Estimated storage capacity is based on a maximum of 10 weight% biochar addition to the upper 30 cm and a

Gt C per year from the atmosphere into biomass (Smith & Collins, 2007). This corresponds to about one-seventh of the CO2 stock in the atmosphere (820 Gt C). However, biomass is not a stable form of carbon material with nearly all returning to the atmosphere in a relatively short time as CO2 because of respiration and biomass decomposition. As a result, using biomass for carbon sequestration is no good option. Any technology that could significantly prolong the lifetime of biomass materials would be helpful to global carbon sequestration. A conversion of only about 7% of the annual terrestrial gross photosynthetic products into a stable biomass carbon material such as biochar would be sufficient to offset the entire amount (nearly 9.7 Gt C a-1) of CO2 emitted into the atmosphere annually from the use of fossil fuels (www.iwr.de). More realistic estimates are that annual net CO2, CH4 and N2O emissions could be reduced by a maximum of 1.8 Pg C a-1 without endangering world food security and soil fertility (Woolf et al., 2010) corresponding to 16% of current anthropogenic CO2 emissions. Therefore, biochar can significantly contribute to climate change mitigation but additional technologies are required to quantitatively offset fossil fuel-derived CO2 emissions. The substitution of fossil fuels by developing and extending renewable energies is another essential key factor for greenhouse gas emission reduction or avoidance while still meeting the basic requirements of electrical or thermic energy consumption demands of society. An impressive example for such a concept is the integrative combination of innovative technologies: a PYREG pyrolysis reactor unit (Gerber 2010), for instance, locally produces biochars from organic wastes in an environmentally friendly way, while also generating heat and electricity from renewable,

Thus, a decentralized application of this technology represents a promising and sustainable

Biochar application to soil influences various soil physico-chemical properties. Due to the high specific surface area of biochar and because of direct nutrient additions via ash or organic fertilizer amendments, nutrient retention and nutrient availability were reported being enhanced after biochar application (Glaser et al., 2002; Pietikäinen et al., 2000). Higher nutrient retention ability, in turn, improves fertilizer use efficiency and reduces leaching (Steiner et al., 2008; Roberts et al., 2010). Most benefits for soil fertility were obtained in highly weathered tropical soils but also higher crop yields of about 30% were obtained upon biochar addition in temperate soils (Verheijen, 2009). Furthermore, enhanced water-holding

**3.6 Can biochar increase soil fertility and thus crop performance?** 

soil bulk density of 1.3 Mg m-3 and 70% stable carbon in biochar (Lee et al., 2010).

carbon neutral resources.

strategy for the future.

According to Ogawa (1994), biochar is generally characterized by a proliferation effect for several symbiosis microorganisms due to its porous structure providing an appropriate habitat for soil microbes. Steiner et al. (2004) observed a significant increase of microbial activity and growth rates by applying biochar to a Ferralsol. Furthermore, an increase of soil microbial biomass and a changed composition of soil microbial community were also observed after biochar amendments (Birk et al., 2009).

While microbial reproduction rates after glucose addition in soils amended with biochar increased, soil respiration rates were not higher (Steiner et al., 2004). This difference between low soil respiration and high microbial population growth potential is one of the characteristics of *terra preta*. These results indicate that a low biodegradable SOM together with a sufficient soil nutrient content are able to support microbial population growth. According to Birk et al. (2009), these effects can be ascribed to different habitat properties in the porous structure of biochar. The following factors might be the reason in decreasing order of currently available evidence supporting them:


Based on these possible stimulating factors, biochar promotes the propagation of useful microorganisms such as free-living nitrogen fixing bacteria (Tryon, 1948; Ogawa, 1994; Nishio, 1996; Rondon et al., 2007). Further reports from Japanese scientists prove increased yields by the stimulation of indigenous arbuscular mycorrhizal fungi (AMF) via the application of biochar (Ogawa, 1994; Nishio, 1996; Saito & Marumoto, 2002): e. g. improved yields for soybeans because of enhanced nodule formation by means of biochar addition (Ogawa et al., 1983). Results from Nishio (1996) obtained with alfalfa (*Medicago sativa*) in pot experiments indicate that biochar was ineffective in stimulating alfalfa growth when added

Synergisms between Compost and Biochar for Sustainable Soil Amelioration 185

Nevertheless, fermentation theoretically provides microorganisms to soil which could be beneficial for soil health and ecosystem services. In a composting / fermentation experiment with and without biochar, the overall C loss during fermentation was about 30% lower when compared to composting (Fig. 5). However, when composting the fermented material, overall OC loss was even higher compared to the composted only material (Fig. 5). This indicates that fermented OM is only stable as long as it was kept anaerobic. As soon as piles were turned (after fermentation) and oxygen became available, the intermediate fermentation products were mineralized to an even higher extent than the non-fermented counterparts (Fig. 5). Biochar addition appeared to amplify fermentation-induced stabilization, since compost piles with 50 (DEM50) and 100 (DEM100) kg biochar per ton of organic feedstock material showed reduced OC loss compared to the fermentation control

Fig. 5. Relative mass balance of organic carbon (OC) during fermentation (Days 1 – 29) and composting (Days 9 – 85; means ± standard error; significant differences between 'Days1-29' OC losses of D0 and DEM0 (see asterisks), p < 0.05, n=3, tested with a Student's t-test). D0, D50 and D100 are composted materials at 0, 50 and 100 kg biochar addition per ton of composted materials, respectively, For DEM 0, 50 and 100 it was the same approach but during the first 29 days of the experiment, these piles were incubated with effective

Fermentation-induced negative priming of fresh OM could indeed be observed, but only as a temporary effect which was reversed during subsequent composting. Thus, fermentation did not result in an enhanced stabilization of compost. A distinct effect of the EM preparation could not be identified (Erben, 2011). Nevertheless, benefits of fermentation in

microorganisms under anaerobic conditions (Erben, 2011).

OM treatment and for soil application remain to be assessed.

without biochar (DEM0, Fig. 5).

to sterilized soil. However, alfalfa shoot weight was increased by a factor of 1.7 and nodule weight by 2.3 times in a treatment receiving biochar, fertilizer and rhizobia compared to a set only treated with fertilizer and rhizobia. According to Nishio (1996), this clearly indicates that the stimulatory effect of adding biochar may appear only when a certain level of indigenous AMF is present. Biochar amendment generally seem to stimulate soil fungi which seems logic as biochar is a complex matrix being degradable only by soil fauna and soil fungi (Birk et al., 2009).
