Biochar and the nitrogen cycle: Unravelling the interaction. Daniel Dempster

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1 Biochar and the nitrogen cycle: Unravelling the interaction Daniel Dempster

2 Acknowledgements My Supervisors Assoc/Prof. Deirdre Gleeson Prof. Daniel Murphy W/Prof. Lyn Abbott Grains Research and Development Corp University of Western Australia Bangor University Prof Davey Jones Liebe Group

3 Biochar What is it? Remnant plant or animal material from pyrolysis Pyrolysis chemical decomposition of organic matter by heating (>250 C) in the absence of oxygen

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5 Previous Research Biochar has been reported to: Improve plant yields and nutrition Increase microbial abundance and activity Increase ph of acidic soils Increase cation exchange capacity Due to sorption of nutrients Increase water retention

6 Western Australian Soils Characterised by: Coarse textured top-soil Low nutrient-holding capacity Low water-holding capacity Biochar is likely to improve soil fertility in WA sands

7 Biochar: The new silver bullet? You may think Improved Fertility Carbon Sequestration Energy Production

8 Various Biochars Poultry Manure Radiata Pine

9 Today Is biochar the silver bullet for agriculture in Australia? How does biochar influence N cycling?

10 Aim To assess how biochar influences the nitrogen cycle in coarse-textured soils of the WA wheatbelt How does biochar influence: Pot experiments: N mineralisation, N leaching? Field experiment: Grain yield, Grain N, Plant N, Soil N?

11 Pot Exp Net N Mineralisation 3 Jarrah biochar rates 0, 5 and 25 t/ha Wheat grown for 10 weeks in sandy soil Expect: Increase with biochar addition

12 Net N Mineralisation mg N/kg dry soil t/ha 5 t/ha 25 t/ha Weeks Incubating

13 Why did N mineralisation decrease? Sorption No Not detected at 5 and 25 t ha -1 biochar addition Immobilisation No Microbial biomass N did not change with biochar addition Toxic compounds on biochar Maybe but undetected Maybe sorption of high molecular weight N compounds

14 Summary Biochar decreased N mineralisation Microbial biomass C Plant growth See Dempster et al., 2012, Plant and Soil for more details Criticism? Sealed pots negate leaching

15 Pot Experiment: Leaching Does biochar alter N leaching on a WA coarsetextured soil? Expect: Decrease Is biochar as good an amendment as sub-soil clay to decrease N leaching? Expect: Yes, better

16 Experimental Design Topsoil treatment (top 10 cm) Control Jarrah Biochar (25 t/ha) homogenously incorporated into top 10 cm Biochar layer (same type and rate) at 10 cm depth Clay (25 t/ha) homogenously mixed to 10 cm Clay layer (same rate and type) at 10 cm depth 40 kg N ha -1 added to each pot

17 mg N / pot 18 Ammonium Leached Control Clay Homogenous Clay Layer Biochar Homogenous Biochar Layer Days

18 mg N / pot Nitrate Leached 20 Control Days Clay Homogenous Clay Layer Biochar Homogenous Biochar Layer

19 Why would N leaching decrease? Sorption: unlikely Increased water-holding capacity Biochar likely to decrease nitrification No effect of different incorporation methods

20 Summary Biochar and clay decreased inorganic N leaching Land managers should use the most readily available source to decrease N leaching See Dempster et al., 2012, Soil Research for more details

21 Field experiment 1) Does biochar influence the required application rate of N fertiliser? Decrease? 2) How does biochar influence grain yield? 3) Does application method make a difference? Trial conducted at the Liebe group Using wheat chaff biochar

22 Design Treatments Biochar Control Spread (4 t/ha) Banded (4 t/ha) Nitrogen Control (0 N) 20 kg N/ha 40 kg N/ha Control Spread Banded Rate of added Nitrogen (kg N/ha)

23 Biochar applied prior to seeding Soil Sampling Pre-biochar application, seeding, re-seeding, terminal spikelet, anthesis, harvest Soil NH 4 + and NO 3 - Plant Sampling Plant Biomass Plant Nitrogen Grain Yield and N

24 No effect on soil N Results No effect on plant or grain N Biochar correlated with a significant difference in plant biomass in one sampling period

25 Grain Yield 2.0 (t/ha) Control Banded Spread Control Banded Spread Control Banded Spread 0 kg N/ha 20 kg N/ha 40 kg N/ha Control plots yielded the most Banded treatments yielded significantly less Plot harvester results showed no difference

26 Summary Wheat chaff biochar did not influence soil or plant N. Hand cuts showed decreased grain yield BUT Trial harvester results showed no difference Wheat chaff biochar application is unlikely to influence grain production or N cycling in a field situation

27 Conclusions Biochar can decrease: Nitrogen mineralisation Nitrogen leaching losses Field application has had very little effect in one year field trial

28 Biochar: the new silver bullet? Results may be different if: Different biochar types are used Biochar is applied to different soil types Different rates of application My experiments: few benefits for the N cycle in coarse-textured soils Unlikely to be a silver bullet for agriculture in WA