Response of soil respiration to the addition of chars - one way to estimate the stability of chars? Jürgen Kern, Giacomo Lanza

Response of soil respiration to the addition of chars - one way to estimate the stability of chars? Jürgen Kern, Giacomo Lanza

Outline Background: Climate change by greenhouse gases CO 2 emission Carbon stability of soil organic matter Carbonisation of biomass >> Contribution to C sequestration Pyrolysis, Hydrothermal carbonisation (HTC) Effects of chars on soil respiration Short-term and long-term experiments in the lab Field experiment with closed chambers (CO 2, δ 13 C) Main question: Is the stability of biochars and other char material predictable?

Greenhouse gases in the atmosphere CO 2 CH 4 N2 O Atmospheric Global Atmospheric Increase of Contribution residence warming concentration concentration to global time (years) potential (1994) (since 1850) warming CO 2 50-200 1 358 ppm 28% 64% CH 4 9-15 21 1720 ppb 146% 20% N 2 O 120 310 312 ppb 13% 6% CHF 3 264 11700 CF 4 50000 6500 72 ppt 0 < 72 ppt SF 6 3200 23900 < 4 ppt 0 < 4 ppt 10%

Carbon loss in agricultural soils Mean carbon loss on European arable soils ( CARBOEUROPE) ~ 0.95 t C ha -1 yr -1

HTC-Autoklaves (1 L, 20 L) Terra Preta in Amazonia ATB Biochar plant Pyrolysis tourque tube

Processes of char production Carbonisation processes Gasification (dry, aerob, > 700 C, C yield < 30%) Pyrolysis (dry, anaerob, 500-900 C, C yield 30-60%) Hydrothermal Carbonisation (aquious medium, anaerob, 180-250 C, 10-50 bar, C yield < 90%) Biokohle-Ausbeute nach der Pyrolyse von Holz C yield within the char (%) Biokohle-Ausbeute (%) 100 80 60 40 20 HTC Pyrolyse Vergasung 0 200 300 400 500 600 700 800 Prozesstemperatur ( C) Process temperature (%)

Pathways of carbonisation Mumme et al. 2011 Structural change to condensed aromatic compounds

Remaining fraction of organic C in soil after 60 days Bioenergy by-products Yeast concentrate (after bioethanol production from wheat) Dried distillers grains with solubles (bioethanol from wheat) Nonfermentables from hydrolysis of wheat straw First-generation biofuels Second- generation biofuels Cattle manure Manures and digestates Cattle manure digestate Wheat straw Poultry manure biochar Biochars Green waste biochar modified from Cayuela et al. (2010) 0 10 20 30 40 50 60 70 80 90 100 Percentage of C remaining in soil (respect to total C)

Our approach Incubation of different char materials mixed with soil Respiration measurement degradation of C compounds (char vs. soil organic matter) Expected effects by Carbon amount / composition Supply of nutrients and energy Duration of incubation Microclimate Microbiota Feedstock Kind of carbonisation, temp. Post-treatment of chars

Design of incubation experiments on the labscale 3-5 g soil + 0.01-3.0 g substrate in 125 ml glas bottles Aerobic conditions at 22 C Rewetted (60-70% WHC) >> anaerobic microzones I. Long-term incubations (>700 days) Different chars II. Middle term incubations (120 days) Different treatments Opening after 1-8 weeks (I. and II.) GC analyses of CO 2 and N 2 O III. Short term incubations (10 days) Different chars and treatments in a dynamic incubation system

I. Incubation for 700 days - Soil and char characteristics Total C Total N C/N C-Emission N-E % % mg CO 2 -C/kg/h µg Sandy soil 1.29 0.13 9.6 0.98 ± 0.35 Terra Preta + soil 4.41 0.28 15.9 5.50 ± 0.21 Peat + soil 13.16 0.46 28.3 16.87 ± 0.34 HTC biochar + soil 56.87 0.12 479.2 5.47 (poplar, 210 C) ± 1.71 Gasifier biochar + soil 75.40 0.78 96.6 0.12 (poplar, 850-900 C ) ± 0.12 Pyrolysis biochar + soil 79.89 0.16 488.9 7.68 (pine, 430 C) ± 1.05

I. Long-term accumulation of CO 2 Cumulative CO 2 -C (mg C g OM -1 ) 60 50 40 30 20 10 0 Natural substrates 30 20 10 0 0 150 300 450 600 750 Days Artificial substrates 0 150 300 450 600 750 Days Sandy soil Terra Preta Peat Sandy soil Gasifier char HTC char Pyrolysis biochar

II. Stability of HTC chars with different treatments in sandy soil after 120 days

II. Comparison of C pathways between straw digestate and its HTC char Carbon remaining after 120 d incubation Mineralized carbon 78 % 64 % Mineralized carbon 3 % 22 % 33 % Conversion losses Straw digestate HTC-Sd-230-w Carbon content of initial straw digestate Schulze et al. (2016) Geoderma 267: 137-145

Influence of different decay kinetics on remaining C Lehmann et al. (2006) Mitigation and Adaptation Strategies for Global Change 11:403-427

III. Short term incubations of treated and non-treated chars for 10 days in a dynamic incubation system Sandy soil + chars (5 g kg -1, Ø 100 µm, untreated) maize straw pyrolysis char (maize silage, 600 C, 30 min) HTC char (maize silage, 210 C, 23 bar, 8 h) + Additives (5 g kg -1, Ø 100 µm) Exp. I: nitrogen (CAN, 27%N) Exp. II: glucose 20 C, 80 ml/min Interval of measurement: 2 h InfraRed Gas Analysis ZALF Müncheberg

Exp. I: Influence of char and N addition on respiration respiration mg CO 2 -C g 1 sample-c 10 20 30 40 a b b c c c c straw HTC HTC+N pyro pyro+n control mineral N Straw > HTC char > pyro char control Nitrogen no increase

Exp. I: Respiration dynamics respiration mg CO 2 -C g 1 sample-c 0 2 4 6 8 10 12 HTC HTC+N pyro pyro+n Lanza et al. (2015). Pedosphere 25: 761-769 0 2 4 6 8 10 12 time (days) 2-stage dynamics for HTC char Nitrogen delays respiration in soil HTC mixtures

Exp. II: Influence of char and glucose addition on respiration a respiration mg CO 2 -C g 1 sample-c 0 20 40 60 80 a b b c d e e glucose HTC+gluc pyro+gluc straw HTC pyro control Glucose >> straw >> chars Glucose + char < glucose

Modelling the decay of biochar in soil Mineralised carbon fraction (%) 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0 200 400 600 800 Control Digestate HTC-digestate Control, mono-exp. Digestate, mono-exp. HTC-Digestate, mono-exp. Control, bi-exp. Digestate, bi-exp. HTC-Digestate, bi-exp. Time after fertilisation (days) Dicke, Lanza et al. (2014) Journal of Environmental Quality 43: 1790-1798

Biochar Persistence in Soil Influence of different C pools on the mean residence time Biochar remaining (% of initial C) 100 80 60 40 20 0 10 yrs Total 712 yrs MRT 100 yrs 1000 yrs 0 20 40 60 80 100 Time (years) Lehmann, presentation at ATB, 28.7.2014

Char application in a field study near Berlin Application of raw and fermented chars from maize silage in September 2012 to increase the soil carbon content from 0.62% to 0.85% Cultivator, plough and split fertilisation with 75 kg N ha -1 in April + May 2013 Crop: winter wheat in October 2012 23

Gas measurements after char application %C δ 13 C Pyrolysis 74,7-12,8 13 C enriched by the feedstock of maize silage HTC 63,6-14,9 Digestate 36,9-16,3 Pyrolysis ferm. 53,7-16,6 HTC ferm. 53,6-16,4 Control 0,9-27,0 Air -11,6

CO 2 flux and isotopic signature Fluss (mgc/m2 h) CO 2 Flux (mg C / m 2 / h) 0 200 400 600 800 100 AB A B B AB B Isotopensignatur ( ) δ¹³c ( ) -32-30 -28-26 -24 Gärrest HTC Kontrolle PyroM thtc tpyrom B A A A A A Gärrest HTC Kontrolle PyroM thtc tpyrom

Conclusions Short term incubations are suitable to compare the effects of different chars on soil respiration Carbonisation process controls the stability of char products Biochars and HTC chars contain different carbon pools Reliability to predict char stability increases with the duration of experiment