Potential soil organic matter benefits from mixed farming: evidence from long-term experiments - David Powlson
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The document evaluates the benefits and drawbacks of mixed farming in enhancing soil organic matter (SOM) and overall soil quality, suggesting that mixed systems may increase SOM while reducing the need for nitrogen fertilizers. Long-term experiments indicate mixed farming contributes to carbon sequestration, aiding in climate change mitigation but may result in lower total crop yields during rotations. Additionally, the incorporation of straw and legumes improves soil physical properties and resilience, despite potentially high costs and economic challenges associated with mixed farming practices.
Potential soil organic matter benefits from mixed farming: evidence from long-term experiments - David Powlson
- 1. Potential soil organic matter benefits from mixed farming: evidence from long-term experiments David Powlson & “Johnny” Johnston Lawes Trust Senior Fellows Department of Sustainable Soils & Grassland Systems Rothamsted Research, UK
- 2. Mixed livestock & arable farming Pros • Recycling nutrients from manure • N inputs from biological N2 fixation in ley phase – decreased need for N fertilizer • SOM content likely to be higher cf continuous arable • Landscape, habitats Cons • Costs of fencing • Costs & labour for animal husbandry • Economics • Inability to specialise (for small enterprises) • Less total grain/arable production during rotation
- 3. Soil – Earth’s Living Skin
- 4. Soil quality Global carbon cycle • Food security • Sustainability Climate change: • mitigation OR • worsening SOM
- 5. Organic inputs and outputs Powlson, Smith, De Nobili (in Soil Conditions and Plant Growth, Eds. PJ Gregory & S Nortcliff, 2013) Results in an equilibrium SOC content characteristic of soil type, climate, cropping system
- 6. Extremes of SOC change in agricultural soils
- 7. SOC changes following land use change, Rothamsted 40 30 20 10 0 1960 90 1940 70 50 80 100 60 20001980 Year -1 Started arable Started grass Johnston et al (2009) Advances in Agronomy 101, 1-57 Movement towards new equilibrium SOC content
- 8. Woburn Ley-arable Experiment (started 1938)
- 9. Continuous arable with fallows Continuous arable 3 year grass/clover ley Woburn Ley/Arable Experiment sandy loam soil, 7% clay, 60 years 3 years “treatment” cropping followed by 2 years arable “test” crops Johnston et al (2009) Advances in Agronomy 101, 1-57 “Treatment” cropping 3 year grass ley + N %C increase ≈ 0.23%
- 10. SOC increases from leys cf continuous arable cropping • Sandy soil: approx. 6.8 t ha-1 in 60 yrs (generous), (but difference established in approx. 30 yrs then no further increase) ≈ 0.2 t C ha-1 yr-1
- 11. Rothamsted Ley/Arable Experiment silty clay loam soil, 23% clay, 36 years 3 years “treatment” cropping followed by 3 years arable “test” crops Johnston et al (2009) Advances in Agronomy 101, 1-57 Increase in %C due to 3 yr leys over 36 yrs
- 12. SOC increases from leys cf continuous arable cropping • Sandy soil: approx. 6.8 t ha-1 in 30 yrs = 0.2 t C ha-1 yr-1 • Silty clay loam soil: approx. 7.2 t ha-1 in 36 yrs = 0.2 t C ha-1 yr-1
- 13. Contribution to decreasing UK GHG emissions • 4.6 Mha arable land • Increased SOC from conversion to ley/arable = 0.2 t C ha-1 yr-1 (generous) = 0.92 Mt C total UK = 3.37 t CO2e total UK • UK annual GHG emissions (DECC 2013, provisional) = 569.9 Mt CO2e • Annual UK GHG emissions savings through soil C sequestration from converting all arable land to ley/arable = 0.6%
- 14. A small change in SOC can have a disproportionately large impact on soil physical properties (“soil quality”)
- 15. Review of straw experiments • 25 experiments, – 6-56 years, Europe, North America, Australia • All had “straw returned” and “straw removed” treatments. • Mainly wheat or barley, some maize, sorghum • Straw removed – mainly baled, in a few cases burned. Powlson, Glendining, Coleman, Whitmore (2011) Agronomy Journal 103, 279 – 287
- 16. • Trend for soil organic C (SOC) content to increase with straw incorporation – but effects small. • Increases only significant in 6 out of 25 experiments, mainly <10%. • Increases in microbial biomass proportionately much greater than for total SOC. Straw results (1/2) Powlson, Glendining, Coleman, Whitmore (2011) Agronomy Journal 103, 279 – 287
- 17. Straw results (2/2) • In some cases soil physical properties measured: – aggregate stability, penetrometer resistance, water infiltration rate – greatly improved with “straw returned” even where no measurable impact on total SOC. – similar results for ‘conservation agriculture’ in Africa and South Asia • Implications for seedling emergence, root growth, water infiltration, decreased soil erosion ……………………. • Evidence from Rothamsted LTEs of positive impact of increased SOC on yield for short-duration crop (spring barley) but not long-duration crop (winter wheat).
- 18. Improved soil structure Greater root exploration of soil More efficient capture of immobile nutrients, e.g. P
- 19. SOC % Grain yield t ha-1 Olsen P to achieve 95% yield Field experiment (spring barley) 1.40 5.00 16 0.87 4.45 45 Pot experiment (grass) 1.40 23 0.87 25 Spring barley grown on low or high OM soil - OM content differed from past manure applications
- 21. • Small increase in SOC cf continuous arable • Small climate change benefit from soil C sequestration – provided not counteracted by grass to arable conversions • Some decrease in N fertilizer use if utilise legumes in ley phase • Improved soil physical structure – agronomic and environmental benefits • More diverse landscapes and habitats BUT • Decreased arable crop production during rotation • Utilisation of pasture • Large changes in agricultural structure required to make economically and practically feasible Arable Mixed arable/grass
- 22. Thanks for your attention
- 23. Extra slides
- 24. After: - Continuous arable 3 year grass ley + N 3 year grass/clover ley Winter wheat Spring barley Johnston & Poulton (2005) SOM influencing crop yield through N supply
- 25. Decline in SOC content in a sandy soil (7% clay) over a 100 years (UK) Johnston et al (2009) Advances in Agronomy 101, 1-57 Continuous cereals, inorganic fertilizers 4 course rotation plus manure
- 27. 0 1 2 3 4 5 6 7 8 9 10 1840 1860 1880 1900 1920 1940 1960 1980 2000 2020 Grain,t/haat85%drymatter Cont wheat Unmanured Cont wheat FYM Cont wheat N3PK 1st wheat FYM+N2 (+N3 since 2005) 1st wheat Best NPK Fallowing Liming Herbicides Fungicides Red Rostock Red Club Sq. Master Red Standard Sq. Master Cappelle D. Flanders Apollo HerewardBrimstone 1st Wheat Cont. wheat Modern cultivars FYM Broadbalk wheat yields, varieties and major chang NPK Grain yield of winter-sown wheat: not very sensitive to SOC concentration, despite improved soil structure in FYM treatment (10 month growing season)
- 28. Example of SOM influencing crop yield – through soil structure or water availability? Hoosfield spring barley - changing yield trends with changes in variety 1976-79 Julia 1988-91 Triumph 1996-99 Cooper 2004-2007 Optic Johnston et al (2009) Advances in Agronomy 101, 1-57 FYM FYM FYM FYM PK PK PK PK Modern cultivars of spring-sown barley (high yield potential): grain yield is sensitive to SOC concentration only (5-6 month growing season) FYM applied 2001 – 2006 only
- 29. Morrow Plots, Illinois Points: measured Lines: RothC simulation 0 10 20 30 40 50 60 70 80 1860 1880 1900 1920 1940 1960 1980 2000 2020 Year SOC(t/hato15cm) Bluegrass Border Continuous Corn Corn-oats -clover C lost to atmosphere Gollany et al (2011) Agronomy Journal 103, 234-246
- 30. Total SOC Small changes from straw return or removal Microbial biomass (and other “active fractions” within total SOC) Changes in response to straw return/removal proportionately much greater Soil physical properties Larger impacts - even when no measureable change in total SOC