Building and Enhancing Soil Biology

TheCan Caesar-TonThat

Research Soil Microbiologist

USDA-ARS, Northern Plains Research Laboratory,

Sidney, Montana

Interactions between soil management and soil biota.

Sustainable soil with emphasis on preservation, enhancement of the soil biota for the benefit of soil structure.

Beneficial Fungi involved in soil aggregation

n Obligate fungi: Mycorrhizal fungi (VAM & ECM)

n Saprophytic fungi: Basidiomycetes

Ligninolytic enzymes.                               

                  Rhizomorphs.

                  “Sticky” mucilage (polysaccharides).

                  Slow-growing fungi; sensitive to soil disturbance (tillage)                                               

Detection of basidiomycetes in field soil using
ELISA (Enzyme-Linked Immunosorbent Assay)

Trends in the basidiomycete populations under different tillage practices

n Basidiomycetes are sensitive to disturbance caused by FALLOW and by TILLAGE.

n Residue quality affect the populations of basidiomycetes.

     (high C:N and lignin:N).

n Fungi are more abundant in the surface of 0-5 cm of NO TILL than Conventional TILL management.

Examples of important Bacterial groups in Agrosystems

n Decomposers of organic materials (plants and animals residues).

         Pseudomonas spp.

n Nitrogen-fixers convert atmospheric nitrogen to ammonium.

Free N₂ fixers: Azobacter spp., Azospirillum brasilense

Symbiotic N₂ fixers: Rhizobium spp.

n Nitrifyers convert ammonium to nitrates. Nitrosomonas spp., Nitrobacter spp.

n Growth-promoting bacteria

         Pseudomonas spp.

n Soil-aggregating bacteria 

Study of soil-aggregating bacteria in microaggregates of two cultivated soils

Teton and Pondera counties, Montana.

Varney-Rothiemay clay loam

Organic matter: 2 - 4 %.

n Continuous barley (40 years), TILL.

n Continuous alfalfa (9 years), NO TILL

n Contrary to the macroaggregates, they are highly stable and resistant to stress.

n They are the building blocks of the macroaggregates.

n They are habitat for many bacteria producing soil

     binding agents.

Approach

n Disrupt the microstructures of microaggregates to release the bacteria.

n Isolate the predominant bacteria inhabiting the microaggregates and purify them.

n Identify the predominant bacterial isolates.

n Prepare artificial aggregates amended with bacteria from different genera.

n Test their water stability.

n Test their resistance to breakage.

Conclusions for this study:

Different species of bacteria with ability to aggregate     and stabilize soil cohabit in consortia in soil         microaggregates.

            More diversity in the communities of soil-aggregating     bacterial in microaggregates of alfalfa soil (NO TILL)   than of barley soil (TILL).