David Rowlings Institute for Sustainable Resources Queensland University of Technology

Transcription

1 How does carbon influence nitrogen availability and losses? David Rowlings Institute for Sustainable Resources Queensland University of Technology

2 Outline Carbon cycle Global carbon cycle Soil carbon 3 main processes governing C & N dynamics Mineralisation Immobilisation Denitrification Global warming potential (GWP) GHG gasses N 2 O CH 4 CO 2

3 Why do we care about soil Carbon? Increased agricultural productivity and sustainability Chemical Main store of nutrients N and K Increased soil ph buffering Biological functions Habitat for soil organisms Energy source for biological processes Contributes to soil resilience Soil physical functions Increased soil stability/structure/aeration Increased water infiltration Increased water holding capacity Moderates changes in soil temperature

4 Global Carbon Cycle CO 2 Atmosphere 800 Gt C +3-5 per year CO 2 ~10 Gt C CO 2 Land Biota 630 Soil and Detritus 1600

5 What is soil carbon? Soil organic carbon (SOC): Carbon stored in the soil Soil organic matter (SOM): includes other important elements such as calcium, hydrogen, oxygen, and nitrogen. SOM is made up of plant and animal materials in various stages of decay.

6 Soil Carbon Cycle Fast Pool Months years Slow Pool years Recalcitrant/passive Pool years Michael J. Singer and Donald N. Munns Soils: An Introduction,

7 Soil C decline: tillage

8 Past Agricultural Practices Erosion Intensive tillage CO 2 Residue removal Soil organic matter Low Productivity

9 SOM sequestration Soil amendments Manure Compost Biochar Agronomic practices Limitations to soil C sequestration Clay content protection Temperature Land management

10 Soil Carbon Cycle Manure High nutrient load and turnover Limited long term effects

11 Soil Carbon Cycle Compost Lower but still high nutrient load Slower nutrient turnover Limited long term effects

12 Soil Carbon Cycle Biochar Low nutrient load Very slow turnover Substantial long term effects

13 SOM sequestration Soil amendments Manure Compost Biochar Agronomic practices Limitations to soil C sequestration Clay content protection Temperature Land management

14 Improved Agricultural Practices Conservation buffers CO 2 Conservation tillage Cover crops Soil organic matter Improved rotations

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17 SOM sequestration Soil amendments Manure Compost Biochar Agronomic practices Limitations to soil C sequestration Clay content protection Temperature Land management

18 Organic matter Mineralization NH 4 + N-cycle Mineralisation Organic compounds in OM simpler compounds or mineralised nutrients. Bacteria and fungi via release of oxidising enzymes oxidation reaction releases energy and carbon which micro-organisms need to live. end product of mineralisation is nutrients in the mineral form. 18

19 Organic matter N-cycle Plant litter production Plant N Plant N-uptake Mineralization NH + 4 NO - Nitrification 3 Death of microbes microbial N-immobilization microbial biomass 19

20 Immobilisation opposite process to mineralisation. mineralised nutrients are incorporated into organic molecules within a living cells. relocates mineral nutrients into pools within the soil that have a relatively rapid turnover time reduces their loss by leaching etc, allowing them to become available to plants. Plants less efficient than microorganisms at taking up mineral nutrients.

21 C:N ratio C inputs If added OM has a lower C:N ratio (higher N content), N is released into the soil. If OM has higher C:N (lower N) microorganisms will utilize the soil nitrogen soil nitrogen will be immobilized and will not be available. Incorporating organic matter that has a high C:N ratio can cause short term plant N deficiency.

22 Organic matter Lucerne: 16-20:1 Clover : 27:1 Manure: 18:1 Wheat straw: 128:1 Plant litter production N-cycle Plant N Plant N-uptake C:N=12:1 Mineralization NH + 4 NO - Nitrification 3 Death of microbes microbial N-immobilization microbial biomass C:N =8:1 22

23 Organic matter Volatilisation (Urea Urine) N Use Efficiency Atmospheric N deposition Plant litter production Plant N Plant N-uptake N 2 O Mineralization NH + 4 NO - Nitrification 3 Denitrification N 2 NO Manure Death of microbes microbial N-immobilization microbial biomass NO 3 losses Leaching runoff N 2 Fixation 23

24 Denitrification N 2 O NO 3 - Denitrification N 2 NO Facultative heterotrophic bacteria Facultative = use N oxides as an alternate electron acceptors when O 2 is limiting: anaerobic conditions Heterotrophic = utilise carbon as a food source NO 3 NO 2 NO + N 2 O N 2

25 Global Warming Potential (GWP) CO 2 equivalents (CO 2 -e) CO 2 = CH 4 = = = = 1 CO 2 -e + = 21 CO 2 -e N 2 O = = + = 296 CO 2 -e CO 2 -e = 1 * CO * CH * N 2 O

26 GWP of a land-use CH 4 consumption in aerobic soils Livestock = CH 4 Fossil fuel consumption = CO 2 N 2 O emissions from soils CO 2 sequestration in vegetation CH 4 production in waterlogged soils Soil organic matter - C storage and decomposition GHG emissions from agriculture

27 C trace gases processes CH 4 produced via decomposition of SOM under anaerobic conditions CH 4 uptake/consumption: Oxidation of CH 4 in aerobic conditions Controlled by O 2 availability and CH 4 diffusion into the soil CO 2 chiefly microbial oxidation of SOM regulated by factors controlling microbial activity - Aeration/ WFPS - Temperature - ph etc...

28 Denitrification rate (N2O-N kg ha day -1 ) C input on N 2 O 200 kg N ha Unamended Mill mud Rice biochar Mud/biochar Mud compost High N compost Huong Unpublished sand silt loam clay loam Carbon added (kg ha) Weier et al. 1993

29 Factors controlling N 2 O production Leaks in the pipes WFPS Substrate availability: size of pipe -Rainfall - Micro-organism food -Aeration - NO - 3 N Mineralization -Vegetation - NH + 4 Fertilization -Bulk density -Soil texture Firestone and Davidson (1989)

30 Precipitation (mm) 25 Temperature ( C) Precipitation (mm) day-1) CO22 (kg (kg C C ha ha-1 CO day -1) CO CO (kgccha day-1 ha-1 2 2(kg 60 WFPS (%) g N2O-N ha-1 yr Mar Mar Apr Apr May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct Nov Nov Dec Dec Jan Jan Feb Feb Mar Mar CH4 (g C ha-1 day-1) g N2O-N ha-1 yr Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar N N22O O (g N ha-1 day-1) 15 CH4 (g C ha-1 day-1) 24-1 day -1)) NN22OO(g day-1 (gnn ha ha-1 WFPS (%) Temperature ( C) Long-term dynamics from a subtropical pasture

31 Precipitation (mm) Precipitation (mm) 25 Temperature ( C) Temperature ( C) Precipitation (mm) (mm) CO2 (kg C ha-1 day-1) Rain events CO2 (kg C ha-1 day-1) 60 WFPS (%) emission pulse Mar Mar Apr Apr May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct Nov Nov Dec Dec Jan Jan Feb Feb Mar Mar CH4 (g C ha-1 day-1) Mar Mar Apr Apr May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct Nov Nov Dec Dec Jan Jan Feb Feb Mar Mar N N22O O (g (g N ha-1 day-1) 15 CH4 (g C ha-1 day-1) 24-1 day NN22O day-1) O (g (g N N ha ha-1 WFPS (%) Temperature ( C) ( C) Controls on emissions

32 N 2 O Mitigation - Fertiliser Use Efficiency Optimizing N fertiliser use = reduced N 2 O + reduced input costs

33 Organic matter Volatilisation (Urea Urine) N Cycle Plant N Plant N-uptake N 2 O Mineralization NH + 4 NO - Nitrification 3 Denitrification N 2 NO NO 3 losses Leaching runoff 33

34 Organic matter Volatilisation (Urea Urine) Inhibitors Plant N Plant N-uptake N 2 O Mineralization Nitrification NH 4 + NO 3 - Denitrification N 2 NO Inhibitor NO 3 losses Leaching runoff 34

35 Questions?