Biochar

Biol Fertil Soils (2002) 35:219–230 DOI 10.1007/s00374-002-0466-4

R E V I E W A RT I C L E

Bruno Glaser · Johannes Lehmann · Wolfgang Zech

Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – a review

Received: 24 April 2001 / Accepted: 5 March 2002 / Published online: 18 April 2002 © Springer-Verlag 2002

Abstract Rapid turnover oforganic matter leads to a low efficiency of organic fertilizers applied to increase and sequester C in soils of the humid tropics. Charcoal was reported to be responsible for high soil organic matter contents and soil fertility of anthropogenic soils (Terra Preta) found in central Amazonia. Therefore, we reviewed the available information about the physical and chemical properties of charcoal asaffected by different combustion procedures, and the effects of its application in agricultural fields on nutrient retention and crop production. Higher nutrient retention and nutrient availability were found after charcoal additions to soil, related to higher exchange capacity, surface area and direct nutrient additions. Higher charring temperatures generally improved exchange properties andsurface area of the charcoal. Additionally, charcoal is relatively recalcitrant and can therefore be used as a long-term sink for atmospheric CO2. Several aspects of a charcoal management system remain unclear, such as the role of microorganisms in oxidizing charcoal surfaces and releasing nutrients and the possibilities to improve charcoal properties during production under field conditions. Severalresearch needs were identified, such as field testing of charcoal production in tropical agroecosystems, the investigation of surface properties of the carbonized materials in the soil environment, and the evaluation of the agronomic and economic effectiveness of soil management with charcoal. Keywords Carbon sequestration · Charcoal addition to soil · Nutrient leaching · Soil amelioration ·Sustainable landuse

Introduction
An intensification of agricultural production on a global scale is necessary in order to secure the food supply for an increasing world population. As a result, fallow periods are often reduced in shifting cultivation in the humid tropics leading to irreversible soil degradation and increased destruction of remaining natural forests due to cultivation of new areasafter slash-and-burn (Vosti et al. 2001). In most tropical environments, sustainable agriculture faces large constraints due to low nutrient contents and accelerated mineralization of soil organic matter (SOM) (Tiessen et al. 1994; Zech et al. 1997). As a consequence, the cation exchange capacity (CEC) of the soils, which is often low due to their clay mineralogy, decreases further. Under suchcircumstances, the efficiency of applied mineral fertilizers is very low when the loss of mobile nutrients such as NO3– or K from the topsoil is enhanced by high rainfall (Melgar et al. 1992; Cahn et al. 1993). Additionally, many farmers cannot afford the costs of regular applications of mineral fertilizers. Therefore, nutrient deficiency is prevalent in many crop production systems of the tropics. Themost common form of landuse in the tropics is shifting cultivation using slash-and-burn techniques. During burning of the aboveground biomass the nutrients are rapidly released into the soil. These nutrient additions have positive effects on soil fertility only for a short period (Cochrane and Sanchez 1980; Kauffman et al. 1995; Kleinman et al. 1995). Additionally, burning releases large amountsof the greenhouse gases CO2 and NOx which lead to global warming (Fearnside et al. 1999). Applications of mulches, composts, and manures have frequently been shown to increase soil fertility. However, under tropical conditions organic matter is usually mineralized very rapidly (Tiessen et al. 1994) and only a small portion of the applied organic compounds will be stabilized in the soil in the...