Slash and Char as Alternative to Slash and Burn
Slash and Char as Alternative to Slash and Burn: soil charcoal amendments maintain soil fertility and establish a carbon sink
Christoph Steiner, www.biochar.org Summary of Dissertation, Faculty of Biology, Chemistry and Geosciences University of Bayreuth, Germany, Institute of Soil Science and Soil Geography, University of Bayreuth, D-95440 Bayreuth, Germany (email: Christoph.Steiner@uni-bayreuth.de)
Tropical forests account for between 20 and 25% of the world terrestrial carbon (C). Soils under tropical forest contain approximately the same amount of C as the lush vegetation above it. The current conversion of Amazonian forest to agricultural land makes disturbance of this C stock important to the global C balance and net greenhouse gas emissions. Changes in land use, particularly by clearing forests, reduce organic C by 20% to 50% in the upper soil layers. Furthermore, this reduction of soil organic matter (SOM) is causing soil degradation. Thus agriculture is not sustainable without nutrient inputs beyond 3 years of cultivation. The efficiency of conventional fertilizers (such as nitrogen (N)) is limited by a low nutrient retention capacity conjoined with strong tropical rains. On the other hand, large amounts of phosphate fertilizers are needed to overcome the soil?s high P-fixation capacity.
To overcome these limitations, slash-and-burn agriculture (shifting cultivation) is practiced by about 300 to 500 million people, affecting almost one third of the planet?s 1500 million ha of arable land. This traditional agricultural practice is considered to be sustainable if adequate fallow periods follow a short time of cultivation. In most agricultural systems the tendency has been for population pressure to increase, leading to shorter fallow periods, and therefore agriculture is doomed to fail without soil fertility management.
The existence of an anthropogenic and C-enriched dark soil in different parts of the world and especially in Amazonia (Amazonian Dark Earths (ADE) or Terra Preta de