**2.2.5 How are plant growth, plant health and crop quality influenced?**

In general, compost creates a favourable environment for plant and root growth especially by


Synergisms between Compost and Biochar for Sustainable Soil Amelioration 179

cause high total carbon losses of 35 – 55 % compared to the initial carbon input by organic feedstocks. This fact indicates that current composting practice may be optimized with respect to a more efficient carbon conservation. Therefore, additional concepts such as *terra* 

In central Amazonia, up to 350 ha wide patches of a pre-Columbian black earth-like anthropogenic soil exist, very well known as *terra preta (de Indio*) characterized by a sustainable enhanced fertility due to high levels of SOM and nutrients such as N, P and Ca (Glaser et al., 2001; Glaser, 2007; Glaser & Birk, 2011). However, the key for *terra preta* formation is the tremendous input of charred organic materials, known as biochar comprising up to 35% of SOM and on average 50 Mg ha-1 (Glaser et al., 2001). Biochar acts as a stable C compound being degraded only slowly with a mean residence time in the millennial time scale. Biochar has a high specific surface area (400 – 800 m2 g-1), it provides a habitat for soil microorganisms which can degrade more labile SOM. In addition, higher microbial activity accelerates soil stabilization as outlined in the previous section. Furthermore, higher mineralization of labile SOM and biochar itself provided important nutrients for plant growth. The general recipe of *terra preta* generation and the principal

*preta* / biochar are required which will be discussed in the following.

Fig. 3. Principles of terra preta formation and soil biochar interaction.

**3. Biochar** 

**3.1 How can biochar improve soils?** 

function of biochar are shown in Fig. 3.

Due to its multiple positive effects on the physical, chemical and biological soil properties, compost contributes to the stabilization and increase of crop productivity and crop quality (Amlinger et al., 2007). Long-term field trials proved that compost has an equalising effect of annual/seasonal fluctuations regarding water, air and heat balance of soils, the availability of plant nutrients and thus the final crop yields (Stöppler et al., 1993; Amlinger et al., 2007). For that reason, a higher yield safety can be expected compared to pure mineral fertilization. Better crop results were often obtained if during the first years higher amounts of compost were applied every 2nd to 3rd year than by applying compost in lower quantities of < 10 Mg (DM) ha-1 every year (Amlinger et al., 2007). However, crop yields after pure compost application were mostly lower when compared to mineral fertilization (Amlinger et al., 2007), at least during the first years. This can be explained by the slow release of nutrients (especially nitrogen) during mineralization of compost.

Compost use does not only improve the growth and productivity of crops in terms of quantity but it could be also proved that quality of agricultural products is influenced in a positive way (Söchtig, 1964; Flaig, 1968; Harms, 1983). By examination of several crops in situ, an increase of beneficial and healthy ingredients and a decrease of harmful substances in the final crop product after compost use compared to a treatment with mineral fertilizer application were observed (Vogtmann et al., 1991). In addition, Fricke et al. (1990) reported significantly higher dry matter content of beet root as well as a lower nitrate level after compost amendment compared to mineral fertilized sets. In a second trial with potatoes, the same authors detected a higher content of starch, vitamin C and dry matter for the composttreated plants compared to the mineral fertilization variant. Furthermore, the portion of marketable potato tubers with respect to the total yield was enhanced in the compost treatment.

In spite of the potential and observed beneficial effects of compost application to agricultural soils, this technique is not widespread across Europe and especially in Germany, low quality composts are produced due to inefficient waste management regulations. In addition, long-term C sequestration potential of compost remains insufficient with respect to mitigation of global atmospheric CO2 increase. Furthermore, as presented by data in Table 5, CO2 emission during the rotting process of compost production generally


Table 5. Relative carbon balance in percent of initial carbon input based on data from Reinhold (2009) concerning composting facilities in Germany.

cause high total carbon losses of 35 – 55 % compared to the initial carbon input by organic feedstocks. This fact indicates that current composting practice may be optimized with respect to a more efficient carbon conservation. Therefore, additional concepts such as *terra preta* / biochar are required which will be discussed in the following.
