THE 4 PER 1000 INITIATIVE: Achievability from Land Management DAVID POWLSON

Transcription

1 THE 4 PER 1000 INITIATIVE: Achievability from Land Management DAVID POWLSON Lawes Trust Senior Fellow Rothamsted Research, UK Visiting Professor in Soil Science University of Reading, UK & Nanjing Agricultural University, China

2 Acknowledgments Paul Poulton, Andy Macdonald, Johnny Johnston: Co-authors of Major limitations to achieving 4 per 1000 increases in SOC: evidence from long-term experiments at Rothamsted Research, UK under review Keith Goulding

3 Big challenges including: Climate change Food security

4 CO 2 emissions from fossil fuels, Global Land Project 36.8 ± 2 Gt CO 2 projected for 2017 = 10.0 Gt C CO 2 emissions from fossil fuels Total GHGs from anthropogenic sources = 13.4 Gt C equiv. Jackson et al (2017) Environmental Research Letters 12,

5 Approx. 2 billion more people by 2050

6 Yield plateau observed for several major crops in many regions e.g. wheat in Netherlands, UK, France Grassini et al (2013) Nature Communications 4: 2918 Likely to be made worse by climate change. e.g. Wheat: 6% yield decrease per 1 C temperature rise. Asseng et al (2015) Nature Climate Change 5,

7 4 per 1000 initiative

8 More organic matter always better! Improves virtually all soil properties BUT: Difficult to increase SOC Slow changes Limited options (practical, agronomic, economic) GOOD NEWS For soil quality & functioning, small increases have large effect (Bad news small loss matters)

9 Climate change mitigation through soil C sequestration Of course do it where possible! Be careful about interpretation of SOC increases is there a net transfer of C from atmospheric CO 2 to soil or vegetation? or avoided emission of CO 2 from soil? What land area available? Don t forget other GHGs from land and agriculture: N 2 O, CH 4

10 Powlson, Whitmore, Goulding (2011) European Journal of Soil Science 62, 42-55

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12 How was 4 calculated? Annual anthropogenic CO 2 emissions from fossil fuels = 8.9 Gt C* Global soil organic C to 2 m depth = 2400 Gt C Emission as percentage of SOC stock = 8.9/2400 x 100 = 0.4% = 4 *Total all anthropogenic GHGs equiv to 13.4 Gt C (IPCC AR5, 2014) ADEME (2015) cited in Minasny et al (2017)

13 Concerns about increasing SOC at 4 yr -1 Difficult to increase SOC to 2m depth - later explanations suggest 1m or 40cm Many global soils are not under human management so cannot be directly influenced Land area* Mkm 2 % Total global Agriculture of which cropland** Forest * ** Ramankutty et al (2008) Global Biogeochemical Cycles 22, GB1003, doi: /2007gb002952

14 Minasny et al (2017) Geoderma 22, Provoked controversy over 4 per mille initiative!

15 A credibility issue for the soil science community? A good initiative but lets manage not only the soil but also the expectations

16 Some issues raised Increasing SOC annually at 4 (0.4%) of initial stock: implies greater C sequestration possible in soils already high in SOC opposite of usual observations soils low in C have potential to increase more Most increases in SOC occur near soil surface (0-30cm) Ignores non-co 2 anthropogenic GHG emissions (N 2 O, CH 4 ) General limitations to soil C sequestration for climate mitigation: Finite in quantity & time, reversible N and P required to accompany C sequestered Potential for SOC loss due to increased temperature

17 Rothamsted LTEs analysed rates of SOC change 16 experiments, 3 soil types, years 114 treatment comparisons Managements included: Manure, composts Straw N fertilizer Ley-arable rotation cf. arable monoculture Green manures Arable converted to grass Arable converted to woodland [Not zero tillage]

18 Annual rates of SOC increase 1-20 yr 18 yr yr 6 yr yr 2 yr yr 1 yr -1 Manure added annually Rothamsted Hoosfield Experiment Spring barley since 1852 FYM applied 35t ha -1 fresh weight (= 225 kg N ha -1 ) Max application permitted in NVZs: = 170 kg N ha -1 = 26 t FYM ha -1 Massive nitrate leaching! Few farmers have so much manure available SOC 4 yr -1 in 0-40cm soil = 7 yr -1 in 0-23cm soil (approx.)

19 Mixed grass/arable cropping Crop rotation Annual SOC change in 35 yr yr -1 (0-25cm) Continuous arable -2 3 yr pasture + 2 yr arable Grass/clover 4 Grass + N 0 Woburn Ley-arable Experiment Arable crops in only 2 years 8yr pasture + 2 yr arable Grass/clover 7 Grass + N out of 10 9 Adapted from: Johnston et al (2017) European Journal of Soil Science 68,

20 Incorporating cereal straw Soil type No. of years Annual SOC change yr -1 Silty clay loam 12 8 Silty clay loam 21 2 Sandy loam 21 5 Review: 25 expts., 6-56 yr, temperate regions General trend for SOC increases But only significant in 6 expts. Improvements in soil biology & physical properties even when no measurable increase in total SOC Powlson et al (2011) Agronomy Journal 103,

21 Organic C. t/ha, 0-69 cm Broadbalk Wilderness: arable to woodland since yr 18 yr yr 13 yr yr 5 yr Year

22 Some points from LTE analysis The 4 yr -1 rate of SOC increase was met in 65% of comparisons BUT Required very major changes in management or land use So severe limitations to achieving this rate in practice (as opposed to experiments) Limitations: Lack of resources at farm level e.g. manure but opportunities for more efficient use Practice already applied e.g. straw retention (~ 50% in UK) most remainder animal bedding Uneconomic e.g. mixed farming but possibility to change through legislation/subsidies Negative impact on global food security e.g. removing land from agriculture

23 Minasny et al (2017) 0-48 yr -1 (mean 12 yr -1 ) 72 examples of SOC increases in experiments BUT: 26%: conversion from arable to grassland or forest removal from food production 29%: organic additions good for soil quality but probably not climate change mitigation 8%: change from all arable to rotations with grass or perennials decreased food production

24 Comments from country case authors in Minasny et al (2017) England and Wales (Ben Marchant) To increase SOC stocks by 4 yr -1 would requires increases of 0.55 t C ha -1 yr -1 Scotland (Laura Poggio and Alessandro Gimona) Peat may sequester t C ha -1 yr -1 Risk of C loss peat converted to agriculture: up to 6.5 t C ha -1 yr -1. To achieve 4 would require C sequestration of 1.7 t C ha -1 yr seems like a very ambitious target..

25 Minasny et al (2017), responding to critics, say: We believe that [4 per mille] is a worthy aspirational target that has also become a slogan in helping the promotion of sustainable soil management Some good slogans: But some bad ones:.

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27 Quote from me: Scientific advice to policy makers should be based on evidence-based reasoning not slogans!

28 Personal concluding comments 1/2 OF COURSE More organic matter in soil always good Good to convince policy-makers of this Need simple messages BUT Must recognise - many limitations to achieving SOC increase at rate of 4 yr -1 over large areas Be truthful, don t exaggerate

29 Personal concluding comments 2/2 Promising too much climate change mitigation to policy makers: risk of losing credibility gives excuse for failing to reduce GHG emissions Better to emphasise SOC enefits for: Sustainable global food security Ecosystem functions Don t forget other GHGs from land management: N 2 O and improving N management CH 4 and ruminant animals feed composition, additives easier to address? Give great emphasis to avoiding land clearance

30 .. give equal attention to stopping this: Deforestation New oil palm on organic soils

31 Thanks for you attention! 175 th wheat crop on Broadbalk Experiment

32 Extra slides

33 Henry Janzen: The soil carbon dilemma: shall we hoard it or use it? Soil Biology & Biochemistry, 38, (2006) Beyond carbon sequestration: soil as conduit of solar energy European Journal of Soil Science, 66, (2015)

34 Comments from country case authors in Minasny et al (2017) England and Wales (Ben Marchant) To increase SOC stocks by 4 yr -1 would requires increases of 0.55 t C ha -1 yr -1 USA (Keith Paustian, Adam Chambers) To achieve this level of C sequestration would require greatly increased investment, either from public or private sources. monitor. evaluate.., adjust programs France (Dominique Arrouays, Manuel Martin, Anne C. Richer-de-Forges, Vera Leatitia Mulder) we must stress that 4 per mille is a finite solution in time and space for climate change mitigation.. long-term solutions to decrease GHG emissions should remain among the policymakers priorities.

35 EDITORIAL 20 NOVEMBER 2017 As climate talks end, it is time for action Worrying disconnect between emissions rhetoric and realworld trends highlights urgent need for nations to honour their pledges. Science can help in other ways..reliable methods of reporting and verifying human-caused CO 2 emissions.. accurate atmospheric measurements to allow carbon researchers to disentangle emissions from human activity and natural processes doi: /d x

36 Environmental Science & Technology 51, (2017)

37 GHG emissions from agriculture, forestry, land use (AFOLU) N 2 O: N fertilizer & manure Methane: livestock, rice Land use change CO 2

38 Applying manure (38 tha -1 ) every 5 th year Crop rotation Annual SOC change in 30 yr yr -1 (0-25cm) Arable (inc. root crops) 0 Arable (inc. 1 yr hay in 5 yrs) 3 3yr lucerne + 2yr arable 6 3yr grazed grass/clover + 2 yr arable 12 arable arable/grass rotation

39 Soil properties Primarily determined by: Texture Mineralogy ph Climate Greatly modified by OM, affecting: Aggregates formation, stability Pores Water infiltration, retention, drainage Soil strength root penetration Fauna & microbes population size, activity, biodiversity Nutrients reserves and availability Nutrient retention - CEC Density Erosion risk..

40 Structure Background to the 4 per 1000 initiative Some criticisms Evidence from long-term experiments Personal conclusions and suggestions

41 Jackson et al (2017) Environmental Research Letters 12, ± 2 Gt CO 2 projected for 2017 = 10.0 Gt C CO 2 emissions from fossil fuels

42 Comments from country case authors in Minasny et al (2017) England and Wales (Ben Marchant) To increase SOC stocks by 4 yr -1 would requires increases of 0.55 t C ha -1 yr -1 Scotland (Laura Poggio and Alessandro Gimona) To achieve 4 would require C sequestration of 1.7 t C ha -1 yr seems a very ambitious target.. like France ((Dominique Arrouays, Manuel Martin, Anne C. Richer-de-Forges, Vera Leatitia Mulder).4 per mille is a finite solution.. long-term solutions to decrease GHG emissions should remain among the policymakers priorities. USA (Keith Paustian, Adam Chambers) To achieve this level of C sequestration would require greatly increased investment, either from public or private sources. monitor. evaluate.., adjust programs

43 Comments from country case authors in Minasny et al (2017) England and Wales (Ben Marchant) To increase SOC stocks by 4 yr -1 would requires increases of 0.55 t C ha -1 yr -1 Scotland (Laura Poggio and Alessandro Gimona) To achieve 4 would require C sequestration of 1.7 t C ha -1 yr seems like a very ambitious target..