Poster: Slash and Char - Soil charcoal amendments maintain soil fertility and create a carbon sink
Christoph Steiner*1, 2, Wenceslau Teixeira2, Thomas Nehls1, Johannes Lehmann3, and Wolfgang Zech1.
1 2 3 Institute of Soil Science, University of Bayreuth, 95440 Bayreuth, Germany; Embrapa Amazonia Ocidental, 69011-970 Manaus, Brazil; Department of Crop and Soil Sciences, Cornell University, Ithaca, NY 14853, USA
* corresponding author: Christop@cpaa.embrapa.br, Christoph.Steiner@uni-bayreuth.de

Introduction
Slash and burn is an agricultural technique widely practiced in the tropics and is considered to be sustainable when fallow periods up to 20 years follow two or three years of agricultural activities. In many parts of the world the increasing population size and socio-economic changes including settlement have made slash-and-burn agriculture unsustainable, leading to soil mining and degradation.

Further Research
In a series of experiments, the use of charcoal in agricultural practice will be examined by evaluating the nutrient losses by leaching. The soil properties under different organic matter applications will be compared with Terra Preta soils.

! The stability of organic matter applications will be investigated in comparison to mineral fertilizer applications in terms of sustainability by using 15N labeled nitrogen and assessing the water and nutrient fluxes.
! SOM formation will be assessed using natural C isotope tracer technique.
! The microbial influence on decomposition and nutrient cycling will be studied in a litter bag experiment and by measuring microbial respiration using the IRGA-based ECT-Soil Respiration Device.
! Soil physical parameters will provide additional information about the influence of SOM and charcoal application to soil.
! Charcoal's sorption capacities for nutrients will be determined by a microbiological experiment.
! An experiment on a banana plantation will test the applicability of the results and the use of charcoal in agricultural practice.
! A socio-economic study will solicit information on household economic activity, demographic composition, and access to land, labor, and capital. Discussions and first-hand observations should provide more general information about production techniques, risks and use of charcoal waste in agriculture.

Methods
Charcoal applications were tested on a Xanthic Oxisol on Terra firme near Manaus. Four treatments in five repetitions were established on 4 m2 plots. Vegetation, litter, and root material was removed from the total field area and aluminum sheets were used as erosion control. The amount of applied charcoal (11125kg/ha) was calculated
from the total soil carbon (C) content to increase total soil C content in the 0-10 cm depth by 25%. The biomass and crop production of sorghum (Sorghum bicolor) was assessed in repeated cropping periods.

Treatments:
! Control (Oxisol)
! Control + mineral fertilizer (N 30, P 35, K
40 & lime 2100 kg/ha)
! Charcoal in powder (11125 kg/ha)
! Charcoal in powder (11125 kg/ha)
+ mineral fertilizer (N 30, P 35, K 40 &
lime 2100 kg/ha)

“Slash and Char”
After clearing the land for agricultural production, farmers use the wood for charcoal production. In charcoal production, approximately 15% of the charcoal output is dust and small pieces (Fig.1c) which are unmarketable. This waste from charcoal production is free, available, and can be used for agricultural purposes.
! Charcoal provides income for rural households. This income could be used to buy organic fertilizer.
! The residues from charcoal production together with chicken manure can increase and maintain the soil's fertility.
! The income from charcoal marketing provides an incentive for longer fallow periods because households practicing slash and char agriculture prefer 8- to 12-year secondary regrowth to primary forest (Coomes and Burt, 1999). The mean fallow period in slash and burnagriculture is 5 years. Longer fallow periods improve soil quality,
charcoal production, and increase the CO re-absorption of the replaced landscape after deforestation and so reduce the carbon dioxide emissions caused by deforestation.
! Charcoal could improve soil physical parameters.
! The regeneration of primary forest species is much greater in areas which are not burnt after felling (Prance, 1975).
! The production of charcoal is CO -neutral if regrowing wood from 2
plantations or secondary forest is used.

Results
The first crop (rice, Oryza sativa) did not show a significant effect of charcoal amendments, probably due to the masking effect of sufficient nutrient supply on all plots. However, during the second cropping period (sorghum, Sorghum bicolor), the charcoal amendments caused a significant increase in plant growth and yield. Plots treated with only charcoal showed the same biomass production as the controls. On these plots (control and charcoal), there was no biomass production at all during the second cropping period. However, the highly significant difference(P<0.001) between NPK plus lime-fertilized plots and plots that received NPK, lime, and charcoal amendments confirms the hypothesis that charcoal has nutrient retention capacities.

Conclusion An agricultural practice of slash and char would provide increased fertility of the soil through active improvement by organic matter applications and through increased fallow periods. Additionally the increased fallow period and the charcoal amendments to soil will create a carbon sink of atmospheric carbon dioxide.

University of Bayreuth
Financial support
BMBF (No. 0339641-57) & CNPq (No. 690003/98-6)

References
Coomes, O. T., and Burt, G. J. (1999). Peasant charcoal production in the Peruvian Amazon: rainforest use and
economic reliance. Forest Ecology and Management 140, 39-50.
Glaser, B., Haumaier, L., Guggenberger, G., and Zech, W. (2001). The "terra preta" phenomenon: a model for
sustainable agriculture in the humid tropics. Naturwissenschaften 88, 37-41.
Glaser, B., Lehmann, J., Steiner, C., Nehls, T., Yousaf, M., and Zech, W. (2002). Potential of pyrolyzed organic matter
in soil amelioration. In "International Soil Conservation Organization Conference”. International Soil
Conservation Organization, Beijing.
Prance, G. T. (1975). The history of the INPA capoeira based on ecological studies of Lecythidaceae. Acta Amazonica
5, 261-263.
Sombroek, W. G. (1966). Amazon soils, a reconnaissance of the soils of the Brazilian Amazon region. dissertation,
Wageningen, The Netherlands.
Zech, W., Haumaier, L., and Hempfling, R. (1990). Ecological aspects of soil organic matter in the tropical land use.
In "Humic substances in soil and crop sciences; selected readings”, pp. 187-202. American Society of Agronomy
and Soil Science Society of America, Madison.
Zech, W., Senesi, N., Guggenberger, G., Kaiser, K., Lehmann, J., Miano, T. M., Miltner, A., and Schroth, G. (1997).
Factors controlling humification and mineralization of soil organic matter in the tropics. Geoderma 79, 117-161.
oil nutrient and carbon contents are generally low in the highly weathered and acid
upland soils of central Amazônia, and soil degradation is mainly caused by a loss of S
soil organic matter (SOM) as CO into the atmosphere and of nutrients into the sub-soil. In 2
these soils, SOM plays a major role in soil productivity because it represents the dominant
reservoir and source of plant nutrients; it also influences pH, cation exchange capacity
(CEC), anion exchange capacity, and soil structure (Zech et al., 1997). Maintaining high
levels of SOM in tropical soils is a step towards sustainability and fertility on tropical
agricultural land, thus reducing the pressure on intact primary forests.
Terra Preta de Indio is a patchily distributed black soil ( C&D) occuring in small areas surounded by the predominantly occuring Oxisols and Ultisols in the Amazon basin.
Because of the similarity in texture to that of immediately surrounding soils, and because of
the occurrence of pre-Columbian ceramics (A&B), these soils are considered man-made
(Glaser et al., 2001; Sombroek, 1966). According to Sombroek (1966) the Terra Preta is
very fertile, and after clearing of forests the soils are not immediately exhausted as the
Oxisols are. Terra Preta contains significantly more carbon, nitrogen, calzium, and
phosphorus, and the CEC, pH value, and base saturation is significantly higher in Terra
Preta soils than in the surrounding Oxisols (Glaser et al., 2002; Zech et al., 1990).