Slash and Char: Soil charcoal amendments maintain soil fertility and create a carbon sink

Tom Miles

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)