Assessment of carbon distribution and soil organic carbon storage in mulch-based cropping systems by using isotopic techniques G. Dercon 1, M. Heiling 1, M. Aigner 1, L. Mayr 1, C. Resch 1, S. Bodé 2, P. Boeckx 2, J. Arrillaga 1, P. Cepuder 3, G. Bodner 3, R. Nolz 3, H. Bock 4, H. Spiegel 4, J. Adu-Gyamfi 1, M.L. Nguyen 1 1 International Atomic Energy Agency, Austria 2 Isotope Bioscience Laboratory, Ghent University, Belgium 3 University of Natural Resources and Life Sciences Vienna (BOKU), Austria 4 Austrian Agency for Health and Food Safety (AGES), Austria Atoms for Food and Agriculture: Meeting the Challenge
Background Better understanding is needed about how soil organic carbon (SOC) accumulation and storage is influenced by: Crop residues Root development factors controlling turnover and stability of the stored SOC, particularly in the deeper soil layers linkage between nitrogen inputs to soil and SOC sequestration transfer phase from conventional to no-tillage mulch-based systems
Coordinated Research Project D1.50.12 Title: Soil Quality and Nutrient Management for Sustainable Food Production in Mulch-based Cropping Systems in Sub- Saharan Africa Objective: To pilot test soil management and agronomic practices in mulch-based agricultural systems that aim to (i) restore soil fertility, optimize ecosystem service efficiency and increase agricultural productivity, while (ii) enhance adaptation and mitigation to climate change in these systems in Sub-Saharan Africa Duration: 2011-2016, 15 participants
Need for analytical tools To monitor the impact of complex land management strategies in enhancing SOC accumulation and storage To assess carbon distribution in the soil profile under on-farm conditions To quantify stability of the stored SOC in agro-ecosystems
Proposed analytical tools are based on Multiple isotope based ( 13 C, 14 C and 15 N) tracing techniques At natural abundance and enriched levels Bulk soil and plant samples SOC fractions Specific organic compounds ( 13 C in fatty acids) for SOC origin Adaptation of modelling tools for assessment of SOC stability or determining SOC origin
SWMCN Laboratory Research Activities Field experiments 1. Groß-Enzersdorf (16 years long-term trial): Chernozem, with SOC (> 2%) 10 km East from Vienna; 2. Grabenegg: Cambisol, with SOC content (1-1.5%) 116 km West from Vienna Greenhouse experiments on two contrasting soils (Seibersdorf FAO/IAEA Laboratories)
Soil Depth Carbon Distribution in Chernozem (Gross-Enzersdorf, Austria) C (%) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 C increase at the surface (1) 0-5 cm 5-10 cm 10-15 cm 15-20 cm Trend of more C in subsoil under Zero-Tillage (3) Conventional Tillage Zero-Tillage Grass Alley 20-40 cm 40-60 cm 60-80 cm 80-100 cm > 50% C stocks in subsoil (2) Single crop under no-tillage for 16 yr
Soil Depth 13 C profile in Chernozem (Gross-Enzersdorf, Austria) δ 13 C ( ) -27.0-26.5-26.0-25.5-25.0-24.5-24.0-23.5-23.0 0-5 cm 5-10 cm 10-15 cm 15-20 cm 20-40 cm Grass: -27.4 Wheat: -25.9 Sugar Beat: -30.0 Maize: -11 (est) 40-60 cm 60-80 cm 80-100 cm Conventional Tillage Zero-Tillage Grass Alley Shift in 13 C signature in the deep soil under different tillage systems
1/C 1/C Carbon contribution in Chernozem (Gross-Enzersdorf, Austria) Application of Balesdent Model (1990) for new and old carbon inputs y = 0.27x + 7.5098 R² = 0.9964 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0-27.00-26.50-26.00-25.50-25.00 1/C Conventional 1/C zero 1/C alley Linear (1/C alley) y = 9.291x + 236.7 R² = 0.7701 y = 9.0137x + 228.88 R² = 0.9677 0-27.00-26.50-26.00-25.50-25.00-24.50-24.00 10 9 8 7 6 5 4 3 2 1 13 C ( ) 13 C ( ) Intercept for X- axis = -27.8 (new carbon inputs under grass alleys) Intercept for X- axis = -25.4 (new carbon inputs under cultivated plots)? Fresh carbon: Grass: -27.4 Wheat: -25.9 Sugar Beat: -30.0 Maize: -11 (est)?
Carbon contribution in Chernozem (Gross-Enzersdorf, Austria) Under the alley (after 16 years): Application of Balesdent Model (1990) for new and old carbon inputs Proportion of old carbon: 0-5 cm 54% 5-10 cm 71% 10-15 cm 82% 15-20 cm 86%.. Can we determine the proportion of carbon inputs by different crops in rotations by using 13 C signature ( ) of specific compounds? Soil Depth Conventional tillage Zero tillage Grass alleys (cm) C16:0 C18:0 C16:0 C18:0 C16:0 C18:0 0-5 31.3 ± 2.7 29.7 ± 0.7 31.2 ± 1.6 30.2 ± 0.6 31.4 ± 0.7 31.3 ± 0.9 10-15 31.2 ± 1.9 29.9 ± 0.1 32.2 ± 2.1 30.2 ± 0.9 32.0 ± 1.6 30.4 ± 0.2 40-60 FA concentrations too low FA concentrations too low FA concentrations too low Low concentrations in the deeper soil Better extraction techniques? Additional specific compounds
δ 13 C in POM ( ) -24.0-24.5 Shift in 13 C signature in Particulate organic matter (POM) Fraction? Soil depth [cm] 0 5 10 15 20 25 30 35 40 45 50 55-25.0-25.5-26.0-26.5-27.0 Shift in 13 C signature under different tillage systems -27.5-28.0 Zero-tillage Conventional tillage alley
Assessing Soil Organic Matter (SOM) Stability particulate organic matter (POM) mineral-associated organic matter (mom) C:N ratio of SOM decreases with decomposition and re-synthesis: N-rich organic compounds are utilised as a C source Excess N is mineralised Leading to 15 N enrichment of the remaining substrate 15 N ( ) Developed for undisturbed ecosystem conditions, but what for agro-ecosystems? Fertilizer-N inputs N dynamics Steady state? Conen et al., 2009
First application of Conen model (Grabenegg Soil, Gleyic Cambisol) 15 N mom 15 N POM C/N C/N [delta] [delta] mom POM mean 6.693 4.695 8.19 14.00 stdev 0.008 0.157 0.02 0.23 Promising results! For mom 15 N increased C:N decreased Good repeatability, in topsoil (less in subsoil) ε -2 ε -5 n n mean 107 58 stdev 16 7 Validation through 14 C-dating is needed to find the right (enrichment factor) is the critical factor (~ isotopic fractionation)
C/N Ratio Conen model application in Chernozem (Gross-Enzersdorf, Austria) 25 20 POM Deep soil POM (40-60 cm) Conv Tillage POM Zero-Tillage POM Alley POM Conv Tillage mom Zero-Tillage mom 15 Alley mom 10 0-5 cm Steady State POM in topsoil mom 5 Surface soil mom (0-5, 10-15 cm) 0 0 2 4 6 8 10 δ 15 N signature (SOC fraction) ( )
Relative Stability Conen model application in Chernozem (Gross-Enzersdorf, Austria) (2) 160 Relative Stability of SOC fractions (POM versus mom) 140 120 100 80 60 40 45.0 80.7 69.1 20 0 16.6 8.1 7.6 9.4 2.5 1.8 0-5 cm 10-15 cm 40-60 cm Soil Depth Conventional Tillage Zero-Tillage Grass Alley
Way forward Better understanding of soil organic carbon sequestration and storage in mulch-based cropping systems Isotopic tools for field-based assessment on soil organic carbon sequestration and stability Training CRP TC project participants in isotopic techniques for soil organic carbon assessment
Many thanks for your attention! CRP D1.50.12 and SWMCN team