This is the presentation deck I used when I spoke about "Soil" at the inaugural Brooklyn Dirt [http://goo.gl/fb/74fjT] on February 16, 2011 at Sycamore Bar and Flowershop.

1. Soil Chris Kreussling (Flatbush Gardener)

2. What is Soil? Physical components Structure Soil Chemistry and Fertility Mineral, Vegetable and Animal: Soil Food Web Soil as Ecosystem

3. Soil Components In this model of a typical healthy soil, roughly half of its volume is space. That space allows for the infiltration and movement of air and water, both of which are critical for life in the soil. Compaction, a common problem with urban soils, reduces this space, preventing air and water from reaching plant roots and soil organisms. Organic matter, including living things, takes up about 5% of volume. Mineral components make up the rest.

4. Mineral Components: Soil Texture Soil’s mineral components are classified by the size of the particles: Sand: .05-2mm Silt: .002-.05mm Clay: <.002mm/2μm Clay particles are roughly the size of bacteria, and smaller. Their small size provides a large surface area in a small volume, contributing to soil fertility. If the largest clay particle (2μm) were the size of a coarse sand grain (2mm), the grain of sand would be 2 meters/6 feet across. Illustration: Richard Wheeler

5. Soil Structure Proportion of space to solids in volume Determined partly by soil texture Bacterial slime and other organic residues contribute to aggregate formation, increasing pore space Organic compounds further increase volume, pore space Compaction reduces proportion of space available for air and water.

6. Plant Nutrients Obtained from air (CO2) and water (H2O): Carbon (C), Hydrogen (H), Oxygen (O) Make up 95% of plant mass The rest obtained from soil Macro-nutrients, more than .1% each: Primary: Nitrogen (N), Phosphorus (P), Potassium (K) Secondary: Ca, Mg, S Micro-nutrients, less than .1% each: Fe, Mn, B, Mo, Cu, Zn, Cl, Co, Na

7. Soil Chemistry Plants require water-soluble ionic (+ or – charge) forms for uptake Different elements typically available as positive ions (cations) or negative ions (anions) Cation Exchange Capacity (CEC) is a measure of soil fertility Clay and organic matter contribute to CEC Cycles: Water, Carbon, Nitrogen pH: Acidity, Alkalinity

8. Nitrogen Cycle

9. pH affects Nutrient Availability Illustration: Monroe County Michigan State University Extension

10. Soil Food Web Trophic Levels Illustration: USDA-NRCS

12. SOM Benefits Microbial carbon and energy source Stabilizes and holds soil particles together Improves soil’s ability to store and transmit air and water Nutrient retention through cation-/anion-exchange Reduces soil density and compaction Makes soil more friable, less sticky, and easier to work Retains carbon Reduces negative environmental effects of pesticides, heavy metals, other pollutants

13. Bacterial-Fungal Biomass Bacteria multiply, opportunistic, benefit from disturbance Fungi grow, benefit from stable soils 1:1, “Bacterially Dominated” Grasslands Agricultural Soils 5:1-10:1: Deciduous Forest 100:1-1000:1: Coniferous Forest

14. It gets weird down there Nematophagous fungi http://www.youtube.com/watch?v=jOwCOLf0IRU

15. References NRCS Soils, http://soils.usda.gov/ Life in the Soil, James B. Nardi