STEWARDSHIP OF THE MICROBIAL ECOSYSTEM OF AGRICULTURAL SOIL. Dr. Bridgitta Steyn Pr.Sci.Nat. 21 August 2018

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1 STEWARDSHIP OF THE MICROBIAL ECOSYSTEM OF AGRICULTURAL SOIL Dr. Bridgitta Steyn Pr.Sci.Nat. 21 August 2018

2 Soil is a basic treasure. Soils produce good yields and keep on doing so if they are well managed. The management of soil is among the oldest of the arts, but none is changing more rapidly than it. We know more about taking care of the soil than our fathers and grandfathers did. There is much more that we should know. Ezra Taft Benson

3 Soil fertility: capacity of soils to supply essential plant nutrients in amounts and forms readily available to plants (or fertility)

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5 Soil Biology and Soil Fertility Least well-understood component Ancient practice dating back to 300BC First inoculant nitrogen years before the Haber-Bosch process Liquid ammonia 450 C 200 atm

6 Soil Fertility Active Immediately available Potential Becomes available Chemical or microbial action on minerals and organic matter Mineralization = Conversion of complex molecular compounds into organic forms carried out by microorganisms

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8 A soil devoid of micro-organisms is a dead soil Jacob Lipman

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11 Some of the organisms associated with the roots are attracted and nourished by molecules secreted from the roots, and then take part in 2- way signaling and exchange of nutrients. This situation clearly parallels the organisms associated with the mucus layer in the colon, where the mucus nourishes the microbiota, which in turn provides nutrients and metabolic signals (e.g. short chain fatty acids) to the host.

12 Kumar et al Frontiers in Plant Science

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22 Building soil health can be accomplished by employing five principles: 1.Armor the soil. 2.Minimize soil disturbance. 3.Increase plant diversity. 4.Keep living roots in the ground all year. 5.Integrate livestock grazing.

23 It holds the soil in place. 1. Armor the Soil Reduces soil evaporation rates. Helps maintain a more moderate range of soil temperatures. Reduces soil compaction by raindrops. Provides a protective habitat for the surface dwellers of the soil food web.

24 2. Minimize Soil Disturbance Biological disturbance = overgrazing Chemical disturbance = over application of nutrients and pesticides Physical disturbance = over time tillage Water erosion Wind erosion Water ponding Easy crusting Depletion of soil organic matter

25 3. Increase Plant Diversity The soil food web use to receive carbon exudates (food) from a diversity of perennial plants, it now receives carbon exudates from only one annual plant species at a time resulting in less biodiversity in the soil food web. Diverse crop rotations provide more diversity, benefiting the soil food web

26 4. Keep Living Roots in the Soil Live plant root exudates = primary food source for the microbial component of the soil food web. Continuous growth of plants throughout the year = root exudates feed the microbial component of the soil without interruption. Cropland systems = usually one crop per season with dormant periods before the next crop is planted. No live plant roots feeding the microbes exudates and they starve to death.

27 Cover crops have the following benefits: Carbon exudates = feed the microbes in the soil food web. Building soil aggregates and pore spaces = improve infiltration. Cover the soil = controlling wind and water erosion, soil temperature and rainfall compaction. Catch and release of inorganic nutrients = improving water quality. Salinity management. Provides food and habitat to pollinators. Weed suppression. Food, habitat and space for wildlife. Integration of livestock to the system. Adding crop diversity. Adjusting the cover crop combination s carbon/nitrogen ratio, to either accelerate or slow decomposition.

28 5. Integrate Livestock Grazing Returning livestock to the system will: Convert high carbon crop residue to low carbon organic material, balancing the C/N ratio with fall or winter grazing. Spring or summer grazing with short exposure periods followed by long recovery periods will allow plants to regrow and harvest additional sunlight and CO2, thereby feeding the microbes in the soil. Grazing of the crop residues in the fields recycles the majority of nutrients, minerals, vitamins and carbon back into the soil. Grazing reduces weed pressure.

29 Soil is essential for the maintenance of biodiversity above and below ground. The wealth of biodiversity below ground is vast and underappreciated: millions of microorganisms live and reproduce in a few grams of topsoil, an ecosystem essential for life on earth Australian Soils and Landscapes, An Illustrated Compendium

30 We are only focusing on the tip of the iceberg, which is the aboveground biodiversity, while the rest of the iceberg, which is the belowground biodiversity, is being neglected

31 Microorganisms = cooks Rhizosphere = kitchen SOM + fertilisers = ingredients/groceries Microbial enzymes = recipes Simple ionic compounds = prepared dishes

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