Soil biological indicators: Organic Farming Systems

Dr. Rachel Creamer, Prof. Bryan Griffiths

Johnstown Castle Environment Research Centre

Acknowledgements: A Bispo – ADEME, Karl Ritz – Cranfield University,

Scottish Agricultural College, SCRI, Dundee

Why does sustainable soil management matter?

Soil Quality

Why soil biology as indicators?

• Soil harbours most of the world’s biodiversity

• Responsible for many key ecosystem functions

• Turnover 50,000 kg fresh material ha-1 yr-1

• Predicted 20 MT CO2-C yr-1 sequestered (NL)

• Soil fauna represent 10% of biomass but are responsible for 30% of N mineralisation

• Cycling of energy and nutrients intimately associated with the soil food web

Biomass

Diversity of soil organisms

Does Size Matter?

Community Structure – Food Web (de Ruiter et al. 1993, J Appl Ecol 30, 95-106)

The soil food web - energy flows

Tulloch, Scotland - Organic Rotation(Scottish Agricultural College)

Intensive Arable Experimental Site, Scotland

Comprehensive set of field measurements

• Soil Physics – air permeability, bulk density, total porosity, macroporosity, available water capacity, and water repellency

• Soil chemistry – NO3-, NH4

+, DOC, DON, pH, soil C:N

• Soil function – Potential nitrification and denitrification rates in lab assay.

- Monthly in situ gas fluxes, CO2, N2O

• Microbiology – Nucleic acid analysis of: nitrifiers, denitrifiers, methanotrophs, eubacteria and fungi. - ELFA, ester-linked fatty acids.

• Soil animals – counted and identified where possible to species. – Earthworms, Microarthropods, Nematodes, Protozoa

Samples taken in 2006 (summer, autumn) and 2007 (spring, summer, autumn). Analytical completion planned for end March 2008

Soil Sustainability ModelGross Visual scorestructure Bulk Density

Air permeabilityPore Water Retention

Physical structure Faunal Pores EarthwormsEnchytraeids

Repellency FungalChemical

pHStructure Chemistry NH4

PNR

Methane oxidisers Bacteria Denitrifiers

Nitrifiers Biodiversity Microbes Eubacteria

FungiQuality Fauna Nematode spp

Earthworm spp

NO3Leaching TEN

DOCLosses CO2 FieldCO2

Gas flux DecompositionN2O FieldN2O

PDR Function

Earthworms Comminution Enchytraeids

Detritivores Collembola Oribatids

Decomposition Bact:Fung B:F ELFAB:F nematodesMicrobivore-nematodes

Mineralisation Microbivores ProtozoaMicrobivore-arthropodsOmnivore-nematodes

Predators Predator-nematodesMesostigmatids

• Control

• All parameters at medium values

• Grassland Organic System

• Increase in decomposition /

biodiversity and recovery of losses

• Arable System

• Added manure increased:

decomposition / physical strength/

chemistry / biodiversity

BUT increased losses of leachates and gases

Model Control

Grassland

Arable

• Marinari et al., 2006 (Ecological Indicators) The field under organic management showed significantly better soil

nutritional and microbiological conditions; with increased level of total nitrogen, nitrate and available phosphorus, and an increased microbial biomass content, and enzymatic activities (acid phosphatase, protease and dehydrogenase). No consistent increase in total organic carbon was observed.

• Birkhofer et al., 2008 (Soil Biology and Biochemistry) Long-term organic farming and the application of farmyard manure

promoted microbial biomass and fostered natural enemies and ecosystem engineers. Application of farmyard manure increased the activity and biomass of decomposer biota. Mineral fertilizers and herbicide application, reduced natural pest control. The combined application of mineral and organic fertilizers appeared to counteract beneficial effects of organic fertilizers, such as enhanced microbial biomass or reduced pest abundance. However 23% higher yields in systems receiving min fertilisers and herbicides

• Fließbach et al., 2006 (Agriculture, Ecosystems and Environment) Both organic C and biological soil quality indicators were clearly

dependent on the quantity and quality of the applied manure types, but soil microbial biomass and activities were much more affected than organic C.

Literature overview

Conclusions

• Organic systems – beneficial for soil biological communities

• Type and quantity of organic matter is important

• Assessment of soil biology can inform on the quality status of soils

• Presence of different trophic groups within Taxa is the best indication e.g. feeding groups of nematodes