J. Kimetu - International Biochar Initiative

Kimetu JM, Lehmann J, Ngoze SO, Mugendi DN, KinyangiJM, Riha S, Verchot L, Bationo A, Thies J and Pell A

Forest soilPrimary forestDegraded soilImmediately after clearingfor cultivation

Decline in soil C stocks with continuous cereal cropping10.0Total organic C (%)8.06.040 4.020 2.000 0.00 20 40 60 80 100 120Time of continuous cultivation (years)

Status of SOMdegradation12 t C/ha/yrTithonia (C-to-N = 9)Quality of theapplied OMBiochar (C-to-N = 380)12 t C/ha/yrSoil texture

CO 2 -C loss from soil surface2500Cumulat tive CO (g m -2 2 -C )200015001000500TithoniaBiocharControlForestSoda lime trap0 27% reduction in CO 2-C loss with biochar compared to control0 100 200 300 400 500Soils with low organic matter (n = 3)Time (days)

100 C recovery in highly degraded soils9083.8%of added d C found in soil)Reco overy (%807060504030201023.7%0Calculated using δ 13 CBiocharTithoniaRepeated application for 3 seasons over 2 year period (n = 3)

Absolute SO OC change(mg g -1 )600.0500.0400.0300.0200.0100.0Stable (Organo-mineral) fractionStabilized (Intra-aggregate) fractionLabile (Free light) fractionGreater proportion pof C in stablefractions per unit Crespired withbiochar than withtithonia0.0-100.0-200.0Tithonia Biochar Tithonia Biochar Tithonia Biochar5 20 105 n = 1; pooled sampleTime since conversion (years)from 3 replicate farms

Absol ute SOC change (mg g -1 )400.0 Stable (organo-mineral) fractionStabilized (intra-aggregate) aggregate) fraction350.0 Labile (free light) fraction300.0250.0200.0150.0100.050.0 000.0-50.00-100.0n = 1; pooled Tithonia Biochar Tithonia Biocharsample from 3replicate farms(20-year oldconversion)SandyClayey

FTIRBiocharTithoniaControlLabile (Free light) fraction‣ Quality of added OMinfluences bothAbsorban nce (arbitrary units)OHOHCH3CH3C=CC=OCH2CH2C=CC=OC-OC-OStabilized (Intra-aggregate)fractionquantity and qualityof protected OM‣ This physically protectedOM is chemically morerecalcitrant t with biocharStable (Organo-mineral)fractionthan with tithonia4000350030002500200015001000Wavenumbers (cm-1)

Rapid oxidation of BC surfacesOc c/C Rati ios1.008 0.80.6Y = 0.117 + 0.546(1 −R2= 0.71,P =0.0404e−0.406t)Particle surface0.4Whole particle0.20.00 20 40 60 80 100Age (years since BC deposition)Nguyen et al., 2008, Biogeochemistry, published online

portion(%)Relati ive pro108Increased carboxyl functional groupsC=O groupY = 1.28 + 2.46 (1 − e62R = 0.76 , P = 0. 0147−0.047t4200 20 40 60 80 100Age (years since BC deposition))Nguyen et al., 2008, Biogeochemistry, published online

Interaction between mineral and BC surfacesParticle cesurfaceRela ative pro oportion (%)12108642AlAluminumWhole particle12108642SiliconSi00 20 40 60 80 10000 20 40 60 80 100Age (years since BC deposition)Nguyen et al., 2008, Biogeochemistry, published online

Interactions with minerals10 μmLehmann, 2007, Frontiers Ecol Environ 5: 381-387Biochar is strongly gyembedded withinminerals and aggregates10 μmTotal CarbonBiocharLehmann et al., 2008, Nature Geoscience 1, 238-242

Lower proportion of both added and pre-existingexistingC is lost with addition of biochar compared totithonia Greater absolute C increase is achieved in highlydegraded soils than in less degraded soils Texture makes almost no difference for biocharbut a lot of difference for tithonia With biochar application, there is more efficientstabilization ti in addition to its chemicalrecalcitrance

Remaining questions:- Why is biochar so stable in soil? What arethe molecular mechanisms of stabilization?- What are the differences in stabilizationmechanisms for different biochars?- Building on this knowledge, how can weu ng n th n w g , h w can wincrease biochar stability in soils?

IBI organizers for invitationit ti Collaborators (Chris Barrett and DavidMbugua) The Rockefeller Foundation and the NationalScience Foundation for core funding ICRAF for helping in logistics Field and laboratory technicians Farmers

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