Click here to load reader

Science and management of soil biology

  • View

  • Download

Embed Size (px)


This is a slightly modified version of a presentation that I shared at the VA No-till Alliance meeting in Harrisonburg, VA on 2/7/2012

Text of Science and management of soil biology

2. Is conventionally managed soil a biological ghosttown? 3. Microherd Even soils receiving intensive tillageand chemical inputs contain billions ofbacteria per gram of soilPhil Brookes 4. The soil beneath our feet may be teeming with a hundred times more species of bacteria than previously thought, according to biologists in New Mexico, US.Measuring the bacterial biodiversity of soil is difficultbecause only a few species can be cultured, according to Jason Gans of the Los Alamos National Lab. Fortunately, biologists can also estimate biodiversityusing a technique called DNA reassociation. This involves chemically unzipping the two strands of all the bacterial DNA in a sample, mixing them up and seeing how longthey take to join up again with matching partners. 5. Their results reveal that there are a fewvery common species in soil but lots of rareSSSAspecies. "There is a very large number oflow abundance species," says Gans. Somany rare species, in fact, that the estimate of bacterial biodiversity rises to ~ 1 million species per gram of soil. 6. How much of the C in these corn stalkswill return to the atmosphere within 1year? > 75% This is not possible without an activemicrobial community 7. Which trajectory forSOM is most commonC in the US?BA150 b/a How is it possible for residue levels toCorn yield increase > 3x withoutbuilding SOM?30 b/a1950 8. Broadbalk continuous wheat experiment Data modelled by RothC-26.3 (solid lines) 100 Organic C in soil NPK systems are both producing > 100 bu/a wheatThe manure and(t C ha-1)Farmyard manure annually 80Soil C (tons/ha) 60Why has the NPK programresulted in so little increase in 40 SOM? NPK 20 unfertilized Unmanured018201840 1860 1880 1900 192019401960 19802000 2020Year 9. The current OM level in a soil is aresult of the long-term balancebetween organic inputs and outputs 10. The current OM level in a soil is aresult of the long-term balancebetween organic inputs and outputsOrganic outputs Yield enhancing practices will not build SOM if OM outputs increase at acomparable rate to OM inputs 11. Drainage + Tillage + Lime + N + harvest = Accelerated loss of SOM But with the removal of water through furrows, ditches, andtiles, and the aeration of the soil by cultivation, what the pioneers did in effect was to fan the former simmering firesinto a blaze of bacterial oxidation and more complete combustion. The combustion of the accumulated organic matter began to take place at a rate far greater than its annual accumulation. Along with the increased rate of destruction ofthe supply accumulated from the past, the removal of cropslessened the chance for annual additions. The age-old processwas reversed and the supply of organic matter in the soil beganto decrease instead of accumulating.William Albrecht 1938 Yearbook of Agriculture 12. How do these soils differ ??manurecover cropscrop residuescrop residues20 years of similar tillage and total organicinput but different types of organic inputs Rodale Institute Farming Systems Trial 13. Granular crumb structurePoor structureThe development of crumb structure isa key step in retaining SOM 14. We are well aware that a poorlybalanced diet for humans results inheart disease, tooth decay,obesity what are theconsequences of feeding soil a white bread diet?White bread diet for soil = very little diversity of organic inputs 15. Unfortunately this is thenorm in agriculture today :-< AcuterootVS.diseaseChronic rootmalfunction 16. Dramatic effect of steamsterilization and compost ongrowth of pepper plants 17. The digestive capacity of soilmicroorganismsgreatly exceedsorganic inputs to soils. 18. Sowhy does organic matteraccumulate at allin soil? 19. In the long run 20. Nature, October 2011 it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readilyRecent analytical and experimental advances havedemonstrated that molecular structure alone does notcontrol SOM stability: in fact, environmental and biological controls predominate 21. Mined humate products mayhave value but are not thesame as old soil organic matter The traditional concept oflarge stable humusmolecules has beenrejected by most scientists 22. Organic matter accumulates under anaerobic conditions Blackland soils ofNorth CarolinaLily (1981) > 1 million acres 23. Impact of temperature on SOM accumulation Organic matter accumulates in climates that support high biomass production but limitOrganic matter dynamicsdecomposition TemperatureBrady and Weil (2002) 24. Organic matter production Impact of temperature on plant growth TemperatureBrady and Weil (2002) 25. Organic matter consumption Impact of temperature on decomposition TemperatureBrady and Weil (2002) 26. Visualizing soilhabitat at biologically relevant scales 27. Worms eye view? 28. Nematodes eye view? 29. Bacteria occupy< 5 % of soil surfacesand < 0.1% of soilporosityVisualizing soil habitat at relevant scales 30. Most of the pores where soilmicroorganisms reside are eitherenvironmentally suppressive or lacking in suitable substrates. 31. Microorganisms have very limited ability to move within the soil matrix. 32. As a result,soil is a very sleepy place !osmobiosis anhydrobiosis thermobiosis anoxybiosis cryobiosis 33. Most soil microorganisms are in a dormant state waiting 34. For their prince charmings to arrive ! 35. RootsRainThere are many types of prince charmings ! TillageOrganic Amendments 36. Dormant earthworm SSSAJ 69(3) cover 37. Earthworm cocoonsoffer much more protection 38. Most plants in yoursoils are in a state of dormancy 39. Seed dormancythanis much better microbialunderstood dormancy 40. Who lives in the soil? Bacteria Body size FungiMicrofloraincreasing Algae Protozoa Microfauna Nematodes Microarthropods Mesofauna Enchytraeids Earthworms Macrofauna Ants, termites, spiders MollusksMegafauna Others: rodents, snakes,voles, amphibians, etc. 41. Most soil organisms widely in sizeSoil organisms vary are tiny !!! Bacteria FungiMicroflora aka microbes Algae Protozoa Microfauna Nematodes Microarthropods Mesofauna Enchytraeids Earthworms Ants, termites, spiders Macrofauna Mollusks Others: rodents, snakes, MegafaunaAbundancevoles, amphibians, etc. 42. Soil microbes carry out> 90% of alldecomposition 43. Soil animals have a disproportionate impact onnutrient cycling, energy fluxes and plant growth 44. Soil animals are mobile but have limited digestive abilitySoil microbes are relatively immobilebut have almost unlimited digestive abilityfungi bacteria 45. 3 main types of digestive interactionsoccur between soil animals and microbes 46. Microbivory +NH4+ NH4NH4+ NH4+NH4+NH4+I want somebacteria for lunch ! Microfauna (e.g. protozoa and nematodes)harness the microbess digestive abilities by grazing on them 47. Externalrumen digestionWhen mesofauna feed on fresh litter, their fecalpellets contain shredded, moistened and mixed but largely undigested residuesReingestion of fecal pellets after a few days ofmicrobial activity greatly increases assimilation 48. Manymicroarthropods use this digestivestrategy 49. Leaf cutter ants are a morewell known example of external rumen digestion 50. Internal rumen digestiongreatly enhances utilization of complex substrates bysoil macrofauna 51. Macrofauna are alsoecosystem engineers 52. Do roots andmacrofauna playsimilar ecologicalroles? 53. Microbial activationStructural modification bacteria root hair rhizoplane Structural modification Microbial activation 54. Navigating the rhizosphere Rhizoplane End of the rhizosphere Endo- Root free soilRhizosphere Ecto-Rhizosphere> 100 X microbialactivity (Lavelle and Spain, 2001) 55. Why do roots have a priming effect? AggregateRelease of protected Disruptionorganic matterGrowing Priming Root EffectExudation Activation of microorganisms(Lavelle and Spain, 2001) 56. Soil in organismsare HOTconcentratedSPOTS ! drilosphereporosphere detritusphereaggregatusphererhizosphereAdapted from Coleman et al. (19??) 57. casts middensDrilosphereZone ofearthworm influence 58. Detrituspherefungisurface residue zone 59. Clean tillageeliminates thedetritusphereMany soil organisms prefer to feed at the surface 60. 3 main strategies forConservation managing soilAugmentationbiology Activation 61. Not all earthworms are sensitive to tillagebut the ones that make vertical burrowsthat connect the topsoil and subsoil are 62. Earthworm functionalcontinuumEpigeic Anecic Endogeic worms worms worms 63. Myco = fungusMycorrhizal diversityRhiza = root EctomycorrhizaeMost woody plantsAM endomycorrhizae Most herbaceousArbutoidplants includingmycorrhizaecorn and soybeansEricoidendomycorrhizaeOrchid endomycorrhizae Lavelle and Spain (2001) 64. Mycorrhizal Networks: Connecting plants intra- and interspecifically Many plants are connected underground by mycorrhizal hyphal interconnections.Mycorrhizal fungiare not very host specific. Illustration by Mark Brundrett Mycorrhizal inoculants are availablebut conservation of established networks is more important 65. Increase nutrient uptakesuppress pathogens (especially P) MycorrhizaeMediate plant competitionImprove soil structureGlomalin Superglue of the soil ?? 66. Are you conserving the beneficialfungi on your crop foliage? 67. Frogeye leafspot fungus resistance to strobilurinchemistry a concern for Mid-South soybean growersHembree Brandon - Mar. 2, 2011 5:36amAdd another to the growing list of weeds, insects, and diseases that havedeveloped resistance to the chemicals that farmers rely on to control pests andprotect yield