Pre-workshop exercise on SOC stock simulation / calibration of DNDC

1. Pre-workshop exercise on SOC stocksimulation / calibration of DNDC Steven Sleutel Dept. Soil Management & Soil Care Ghent University

2. DNDC model DNDC: C and N bio-geochemical model • Li et al. (1992; 1994) • 2 components: • 1° soil climate, crop growth, decomposition • 2° nitrification, denitrification, fermentation • 4 SOC pools (litter, microbial biomass, active humus, passive humus) • Daily time steps • possibilities to define “management” (tillage, N-fertilization, manuring, cropping dates)

3. INPUT SOIL VAR. DNDC model stucture (process oriented, 6 different sub-modules) CO2 decomposition

4. DNDC model Own Interest: • prediction SOC stock changes cropland soils (regional scale: SOC storage potential) • denitrification – fermentation –SOC cycle plant phenological growth sub modules • “User” -> limited access to parameterization specific model processes

5. Model exercise data input • Climate: daily T° and precipitation • Soil variables: bulk density, SOC conc., pH, clay content, moisture content at wilting point and field capacity, land-use • Management: crop rotation and dates of sowing and harvest, tillage, N-fertilization, manuring Specific DNDC paramerization for model exercise • Partitioning of C and N in crop parts – C:N ratio’s • crop yields at optimum conditions (N, water, temp.) • Initial partitioning of SOC in model pools • “Soil microbial activity index”

6. Proposed model simulations

7. Proposed model simulations

8. Parmeter sets

9. Calibration of crop param. Plot12 Year 8 Year 1-2 Large underestimation of crop yields adjust DNDC’s crop par. to 1° 2° 3°

10. Calibration of crop param. Plot 12 Spring barley Large underestimation of crop yields adjust DNDC’s crop par. to 1° starting date of growth of grain 2° 3°

11. Calibration of crop param. Plot 12 Large underestimation of crop yields adjust DNDC’s crop par. to 1° starting date of growth of grain 2° measured C and N content plant parts partitioning C plant parts (grain / shoot / root) 3°

12. Calibration of crop param. Plot 12 Large underestimation of crop yields adjust DNDC’s crop par. to 1° starting date of growth of grain 2° measured C and N content plant parts partitioning C plant parts (grain / shoot / root) 3° DNDC par. “optimum yield”

14. Proposed model simulations

15. Simulation of SOC stock evolution plot 13 crop rotation with 4 crops • SB – B – PO – WW • Average figures: yield (kg DM) fertilization (type, amount, date) tillage (depth, date) sowing and harvest date • 2 crop rotations: management changes with time: higher N-fertilization (1° 70y; 2° 30y) Crop rot. 2 higher N-fert. Crop rot. 1 1972 2002 1902

16. Simulation 100y NPK (plot 13) default DNDC crop par. Underestimation of crop yields

17. Simulation 100y NPK (plot 13)with crop par. ~ plot 12 Overestimation of crop yield PO

18. Simulation 100y NPK (plot 13)default DNDC crop parameters

19. Simulation 100y NPK (plot 13)crop parameters adj. plot 12 Large underestimation SOC conc. Further calibration DNDC on plot 12:Calibration II.b

20. Proposed model simulations

22. Simulation 8y plot 12 overestimation SOC conc. Adjust initial partitioning DNDC’s SOC pools (default = 80 % humus)

23. Tot. RMSE (kg OC kg-1 soil) 0.0009

24. Simulation 8y plot 12 overestimation SOC conc. Adjust initial partitioning DNDC’s SOC pools (default = 80 % humus)

25. Simulation 8y plot 12 overestimation SOC conc. Adjust initial partitioning DNDC’s SOC pools (75 % humus)

26. Simulation 8y plot 12 overestimation SOC conc. Adjust initial partitioning DNDC’s SOC pools (70 % humus)

27. Tot. RMSE plot 12 (kg OC kg-1 soil) 0.0009 0.00072

28. Simulation 100y NPK (plot 13) default DNDC 80% humus Calibration

29. Simulation 100y NPK (plot 13) 70% humus ~ calibration plot 12 Worse simulation of SOC conc.

30. Tot. RMSE plot 12 (kg OC kg-1 soil) 0.0009 0.00072

31. Simulation 8y plot 12 Adjust DNDC’s “Microbial Activity Index” (0-1) Default value 1

32. Simulation 8y plot 12 Adjust DNDC’s “Microbial Activity Index” (0-1) 0.9

33. Simulation 8y plot 12 Adjust DNDC’s “Microbial Activity Index” (0-1) 0.8

34. Simulation 8y plot 12 Adjust DNDC’s “Microbial Activity Index” (0-1) 0.7

35. Tot. RMSE plot 12 (kg OC kg-1 soil) 0.0009 0.00072 0.00073

36. Simulation 100y NPK (plot 13) 70% humus ~ calibration plot 12 Microbial Activity index = 1 (default DNDC)

37. Simulation 100y NPK (plot 13) 70% humus ~ calibration plot 12 Almost no improvement Microbial Activity index = 0.9 ~ plot 12

38. Simulation 100y nil (plot 18) 80% humus (default DNDC) Microbial Activity index = 1 (default DNDC)

39. Simulation 100y nil (plot 18) 70% humus ~ plot 12 Microbial Activity index = 0.9

41. Simulation 100y NPK (plot 13) 70% humus ~ calibration plot 12 Slightly better Microbial Activity index = 0.9 ~ plot 12

42. Simulation 100y NPK (plot 13) 90% humus ~ plot 12 Microbial Activity index = 0.7

43. Simulation 100y NPK (plot 13) 90% humus ~ plot 12 Microbial Activity index = 0.6

44. Simulation 100y NPK (plot 13) 90% humus ~ plot 12 Microbial Activity index = 0.5

45. Simulation 100y nil (plot 18) 70% humus ~ plot 12 Microbial Activity index = 0.9

46. Simulation 100y nil (plot 18) 90% humus ~ plot 12 Microbial Activity index = 0.6

47. Simulation 100y FYM (plot 6) Better result: Plot 6 OM input ~correspond To plot 12 70% humus ~ plot 12 Microbial Activity index = 0.9

48. Simulation 100y FYM (plot 6) 90% humus Microbial Activity index = 1

49. conclusions • Good Calibration plot 12 -> bad result sim. plots: impossible to estimate error for long-term aplic. • 8y is too short to calibrate SOC pool partitioning, which has a large impact on the final result of the long-term simulations • “correspondence in management” between calibration plot and simulation plots is necessary: plot 12 – plot 13 & 18 • Calibration of other parameters DNDC: specific decomposition rates SOC pools, • Simplicity of DNDC: partitioning of fresh OM based only on C:N-ratio • Requiered data: partitioning of SOM??