Tree-based intercropping: A land-use system to enhance carbon sequestration in agricultural landscapes in Canada

Transcription

1 Tree-based intercropping: A land-use system to enhance carbon sequestration in agricultural landscapes in Canada by Amy Wotherspoon, Naresh Thevathasan, Andrew Gordon and Paul Voroney School of Environmental Sciences University of Guelph, Guelph, Ontario Canada June 3, th North American Agroforestry Conference, Ames, Iowa 1

2 TBI in Southwestern Ontario 2

3 UoG Agroforestry Research Station Established in 1987 Soil: sandy loam; calcareous parent material Density: 111 trees ha -1, RCBD Tree row spacing: m Within row spacing: 3 6 m 3 3

4 Gaps in Current Research Lack of empirical data for TBI systems and for specific tree species on C seq. Lack of data on belowground pools in TBI Carbon seq. over time in TBI systems -25 years? Carbon sequestration potential of TBI systems, when compared to conventional agriculture systems? 4

5 Research Objectives 1. Quantify above and belowground carbon pools in tree biomass and soil 2. Determine quantity and quality of C fluxes 3. Compare these carbon pools and fluxes in TBI to conventional agricultural systems. Adapted from Peichl et al.,

6 Tree Species 25 years old Poplar hybrid (Populus sp.) Black walnut (Juglans negro) Red oak (Quercus rubra) 111 trees ha trees ha -1 Norway spruce (Picea abies) 333 trees ha -1 White cedar (Thuja occidentalis) 6 6

7 Agricultural Crops Maize (Zea mays) Winter Wheat (Triticum aestivum) Soybean (Glycine max) Barley (Hordeum vulgare) 7

8 Carbon Pools Aboveground tree biomass Belowground tree biomass Soil organic carbon 8

9 C Pools Above- and Belowground C Quantification 3 trees per species were destructively harvested Measured DBH, height, mass and C concentration of each component Tree components were separated as: trunk, primary and secondary branches, twigs and leaves and roots. Root excavation to 24 m 3 (4m x 4m x 1.5m) 9

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11 C Pools Soil Organic Carbon East and West direction Distance from tree: 0.5, 1.0, 1.5, 2.0 m Depth below surface: 0-10, 10-20, cm Fumigated with 12 M HCl to remove inorganic carbon Analyzed for organic C concentration using LECO CR-12 Carbon Analyzer 11

12 C Pools: Findings Tree Carbon Mean carbon content of individual tree components for hybrid poplar (n=3) growing in a 25-year-old TBI system Carbon Biomass dry Carbon content concentration weight (kg) (kg C) (%) Trunk (+ 61.9) 51 (+ 1.9) (+ 28.6) Primary 91.8 (+ 62.3) 53 (+ 1.1) 48.0 (+ 32.4) Secondary 48.3 (+ 40.8) 53 (+ 1.6) 25.4 (+ 21.3) Twigs 25.9 (+ 4.6) 53 (+ 0.3) 13.7 (+ 2.5) Roots (+ 54.4) 50 (+ 4.0) 52.3 (+ 31.9) TOTAL ( ) Chapter 1: C Pools (Findings) 12

13 Mean Carbon Content (kg C) C Pools: Findings Tree Carbon Figure 1. Mean carbon content (kg C) for each tree component plus mean carbon concentration (%) for five TBI tree species Chapter 1: C Pools (Findings) a b b bc c Twigs Secondary Primary Trunk Roots Average [C] (%) 50 0 Hybrid Poplar Red Oak Black Walnut Norway Spruce White Cedar Tree Species 13

14 Carbon Concentration (%) C Pools: Findings SOC Soybean Poplar Oak Walnut Spruce Cedar Plant Species 0-10cm 10-20cm 20-40cm Chapter 1: C Pools (Findings) Figure 2: Soil organic carbon concentration (%) at 0-10, and cm depths below five tree species from a 25-yearold TBI system and an adjacent soybean monocrop system 15

15 C Pools: Findings SOC Pools Mean bulk densities (+ SE) and SOC pools associated with 25-year-old TBI and conventional agricultural systems (0-40 cm) in southern Ontario. Hybrid Poplar C Content (%) Mean Bulk Density (g cm -3 ) SOC Pool (t C ha -1 ) (+ 0.11) 1.21 (+ 0.12) Red Oak (+ 0.12) 1.20 (+ 0.13) Black Walnut (+ 0.10) 1.14 (+ 0.19) Norway Spruce (+ 0.14) 1.15 (+ 0.18) White Cedar (+ 0.13) 1.15 (+ 0.18) Soybean Monocrop (+ 0.18) Chapter 1: C Pools (Findings) 16

16 C Pools: Significance Summary of carbon pools (t C ha -1 ) for five tree species in a 25-year-old TBI system as compared to a conventional agricultural system in southwestern Ontario. Hybrid Poplar Red Oak Black Walnut Norway Spruce White Cedar Soybean Monocrop Chapter 1: C Pools (Significance) Tree C Content SOC Total Ratio of species: soybean 1.6:1 1.4:1 1.4:1 1.5:1 1.4:1 17

17 C Pools: Significance Comparison of biomass carbon (t C ha -1 ) for two tree species in a TBI system in southern Ontario from 13 to 25 years after establishment. Tree C Content Hybrid Poplar Norway Spruce 13 years after establishment Chapter 1: C Pools (Significance) 25 years after establishment Difference Poplar: from 1.17 to 1.06 t C ha -1 year -1 between 13 and 25 years after establishment (Peichl et al., 2006) 18 Spruce: from 0.49 to 0.52 t C ha -1 year -1 between 13 and 25 years after establishment (Peichl et al., 2006)

18 C Pools: Significance Summary of soil carbon pool (t C ha -1 ) difference between 13 years and 25 years after the establishment of the TBI system as compared to a conventional agricultural system in southwestern Ontario. SOC Hybrid Poplar Norway Spruce Soybean Monocrop 13 years after establishment years after establishment Difference Soybean monocrop agriculture system has 15.8 t C ha -1 less than poplar Soybean monocrop agriculture system has 7.2 t C ha -1 less than spruce 19

19 Carbon Fluxes Litterfall Litter Decomposition Soil Respiration 20

20 C Fluxes Litterfall and Litter Decomposition Litter collected from 72 1-m 2 traps (2 mm mesh) between Sept Dec 2012 Decomposition measured from cm 2 2-mm mesh bags between Oct 2012 and

21 C Fluxes Tree Litter trap Decomposition bags Soil respiration chambers 0 m 1m P S C 2 m W O SB-L Sampling period SB-S 6 m 23

22 C Fluxes: Findings - Litterfall Annual flux (g m -2 ) for litterfall and other trap contents for five tree species in a 25-year-old TBI system (+ SE) Total Litterfall Other leaves Woody debris Other (fruits, seeds, buds. twigs, etc.) Walnut (+ 20) 21.1 (+ 30) 34 (+ 45) (+ 98) Poplar (+ 19) 70.4 (+ 61) 73.5 (+ 11) 37.8 (+ 18) Spruce 58.9 (+ 19) 75.3 (+ 50) 66.5 (+ 41) 37.8 (+ 16) Oak (+ 98) 35.2 (+ 24) (+ 49) 80.6 (+ 34) Cedar 32.7 (+ 8) (+ 46) 58.8 (+ 9) 12.8 (+ 8) 26

23 Mass Remaining (%) C Fluxes: Findings Litter Decomposition Poplar Oak Walnut Spruce Cedar Oct (12) Nov (12) Jan (13) Apr (13) Jun (13) Aug (13)Sep (13) Oct (13) Time Figure 3. Leaf biomass remaining after 12 months from five different tree species in a 25-year-old TBI system 27

24 Mass Remaining (%) C Fluxes: Findings Litter Decomposition 100 Soybean Stalk Soybean Stalk (TBI) Soybean Leaf Soybean Leaf (TBI) Oct (12) Nov (12) Jan (13) Apr (13) Jun (13) Aug (13) Sep (13) Oct (13) Time Figure 4. Leaf biomass remaining after 12 months of soybean stalk and leaf in a 25-year-old TBI system compared to a soybean monocrop system 28

25 C Fluxes: Findings C inputs & outputs Table 7. Accumulation of C inputs and outputs from litterfall and litter decomposition for five tree species in a 25-year-old TBI system Litterfall (t ha -1 y -1 ) C input (t C ha -1 y -1 ) Biomass decomposition (%) C Output (t C ha -1 y -1 ) Poplar Walnut Oak Spruce Cedar Assuming 43% C content for deciduous trees and 50% C for conifer trees 29

26 C Fluxes Soil Respiration Soda lime method for annual CO 2 fluxes Measured monthly June 2012 May 2013 Tree species: Poplar, walnut, spruce at 0, 2 and 6 m from the tree row 31

27 Soil Respiration (g CO 2 m -2 d -1 ) C Fluxes: Findings Soil 30 Respiration Conversion to annual C efflux: Poplar = 6.35 (+ 1.09) Walnut = 5.93 (+ 1.10) Spruce = 5.86 (+ 1.22) Soybean = 4.57 (+ 0.23) t C ha -1 year -1 Feb(13) Apr(13) May(13) June(12) July(12) Aug(12) Sept(12) Oct(12) Nov(12) Dec(12) Time 0m 2m 6m Soybean Monocrop Temperature Figure 6. Mean monthly soil respiration (g CO 2 m -2 d -1 ) of a 25- year-old TBI system in comparison to a soybean monocrop along with mean monthly temperature ( C) 32

28 Comparing TBI to conventional agriculture 33

29 TBI vs. Conventional Agriculture Table 8. Annual carbon inputs (t C ha -1 y -1 ) from five tree species commonly grown in treebased intercropping systems in comparison to conventional agricultural system planted with soybean) Aboveground tree C assimilation Belowground tree C assimilation Poplar Oak Walnut Spruce Cedar Soybean Litterfall C inputs Fine root turnover Above and belowground Crop C input 1 Total inputs Harvested soybean data obtained from Peng et al. (2012) 34

30 TBI vs. Conventional Agriculture Table 9. Annual carbon outputs (t C ha -1 y -1 ) from five tree species commonly grown in treebased intercropping systems in comparison to conventional agricultural system planted with soybean) Poplar Oak Walnut Spruce Cedar Soybean Litterfall C outputs Root C output Crop C output C leachate Total outputs Harvested soybean data obtained from Peng et al. (2012) 2 Assuming C leaching rate of 200 mm y -1 (Peichl et al., 2006) 35

31 TBI vs. Conventional Agriculture Table 10. Annual net carbon (t C ha -1 y -1 ) from five tree species commonly grown in tree-based intercropping systems in comparison to conventional agricultural system (planted with soybean) Poplar Oak Walnut Spruce Cedar Soybean Total inputs Total outputs Net Carbon

32 Summary and Final Thoughts TBI planted with hybrid poplar, red oak, black walnut, Norway spruce, and white cedar all have greater CSP when compared to conventional agriculture (soybean) The presence of perennial tree above and belowground C contribution Contribution of organic matter to the long term stable SOC pool 13 years Vs 25 years after establishment Crop rotation is important to maintain SOC levels in agricultural systems negative net loss of C in this study (soybean) 37

33 Future Work New Information The CSP of a long term TBI system CSP of five different tree species commonly found in TBI systems New Direction Fast growing species may need several short-term cutting cycles Slow growing species will continue to sequester atmospheric C Can assess their CSP in various agroforestry systems (windbreaks, riparian buffers, etc.) Can assess the various economic returns based on each species contribution Net CSP can contribute towards carbon trading 39

34 Acknowledgement Funding received from the Agriculture and AgriFood Canada s Agricultural Greenhouse Gas Program (AGGP), Government of Canada, is greatefuly acknowledged. 40

35 THANK YOU 41

36 Additional Information 42

37 Outline Introduction - TBI land-use and climate change mitigation Carbon Pools Above- and belowground biomass Soil organic carbon (SOC) Carbon Fluxes Litterfall Litter decomposition Soil respiration TBI vs. Conventional Agriculture Net carbon sequestration potential Summary and final thoughts 43

38 TBI to mitigate climate change Atmospheric carbon dioxide sequestration (perennial tree) and trees can act as a long term C sink Litterfall and root turnover returns C to the system and contributes to the long term soil carbon pool 44

39 Methods Litterfall Traps # of Traps Poplar 6 # of Reps Total 18 Oak 6 18 Walnut Spruce 4 12 Cedar 2 6 Total # of Traps 72 Location Litter Decomposition Bags # of Species # of Reps Total # of bags TBI Soybean monocrop Total (per sampling period) 25 X 7 sampling periods

40 Fertilizer rates Commercial N fertilizer was applied prior to planting at: 124 kg N ha -1 y -1, 93 kg P ha-1 y-1 and 46 kg K ha -1 y -1 for maize 117 kg N ha -1 y -1, 45 kg K ha -1 y -1 and 86 kg K ha -1 y -1 for wheat 30 kg K ha -1 y -1 for soybeans (Oelbermann et al., 2006) 48

41 HCl Fumigation Correction Factor The following chemical reaction occurs during fumigation of soil with 12 M HCl -CO 3 (s) + 2HCl (g) + - CL 2 (s) + H 2 O Change in mass of CL 2 formed (70.91 g mol -1 ) is greater than the original CO 3 (60.01 g mol -1 ) The correction factor expresses SOC content on a pre-treated soil mass basis and converts mass of the acid fumigated soil analyzed in the LECO to an equivalent mass of untreated soil. Ramnarie et al. (2011) 49

42 HCl Fumigation Correction Factor cont d Initial soil weight converted to oven dry weight using gravimetric moisture content Calculate mass change between oven dry weight after addition of acid to before addition of acid That mass change is added to the fresh weight of the amount of soil that is added into the LECO (i.e ) Correction factor: (final oven dry soil weight after acid) (initial oven dry soil weight before acid)/(initial oven dry soil weight before acid) And then: % Organic C is multiplied by correction factor to become calculated % organic C 50

43 Importance of crop rotation Disease and pest prevention Increasing yields Corn planted after corn shows reduced yield Balancing soil fertility Corn depletes N and P which can then be replenished by planting soybean Soybean can be tilled and return N to the soil. Can also be harvested and marketed. Wheat provides continuous ground cover and increases available N and can be easily planted between the leftover soybean stubble. 51