Slash and CharSoil charcoal amendments maintain soil fertility and create a carbon sink

1, 2 2 1 3 1Christoph Steiner* , Wenceslau Teixeira , Thomas Nehls , Johannes Lehmann , and Wolfgang Zech .

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

Introductionlash 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 Syears 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 Reasearch

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 15sustainability by using N labeled nitrogen and assessing the water and nutrient fluxes.

13! 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.

MethodsCharcoal applications were tested on a Xanthic

Oxisol on Terra firme near Manaus. Four

treatments in five repetitions were established on 4 2m 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 burn

agriculture is 5 years. Longer fallow periods improve soil quality,

charcoal production, and increase the CO re-absorption of the 2

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.

0

0 .2

0 .4

0 .6

0 .8

1

1 .2

1 .4

1 .6

B io m a s s Y ie ld T o ta l

w ith c h a rc o a l

w ith o ut c h a rc o a l

267%

881%

366%

ResultsThe 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.

ConclusionAn 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 Ssoil 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.

erra Preta de Indio is a patchily distributed black soil ( C&D) occuring in small areas T 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).

harcoal and highly aromatic humic substances are a characteristic of Terra Preta.

This suggests that residues of incomplete combustion of organic material (black Ccarbon) are a key factor in the persistence of SOM in these soils. Terra Preta soils contain

up to 70 times more black carbon than the surrounding soils (Glaser et al., 2001) . It can be

concluded that in highly weathered tropical soils, SOM and especially charcoal plays a key

role in maintaining soil fertility.

Acknowledgements

Organic scientific farming is a intensive work. We are grateful to all the fieldworkers in particular to Francisco Aragão Simão and the field technician Luciana Ferreira da Silva. We thank Marcia Pereira de Almeida for her work in the laboratory. Besides all other colloquies, who provided us with valuable help, we appreciate the support of Jeferson Vasconcelos and Jose Pereira da Silva Jr. Ilse Ackermann offered photographs for a better illustration.

Fig.4 treatment with additional soil charcoal application (55 days after planting)

Fig.3 treatment fertilized with NPK and lime (55 days after planting)

Fig.2 compares treatments with and without soil charcoal application. Biomass, yield and total biomass is given in tons per hectare the increase is given in percent.. The error bars indicate the standard error.

Foto: Ilse Ackermann

Foto: Ilse Ackermann

Foto: Ilse Ackermann

a cb

Fig.1 illustrates "slash and char” agriculture: a = homegarden with charcoal residues, b = Banana planting hole filled with soil, chicken manure and charcoal, c = charcoal residues (powder and small pieces) at the sieve table. From Steiner et al 2004, Chapter 14, Springer Verlag

A

DC

B