1. Chapter 10 - Soil Fertility

2. Essential Plant Nutrients - 14 are Mineral Based Macros - N, P, K, Ca, Mg, S Micros - B, Cu, Cl, Fe, Mn, Mo, Zn, Ni

3. Nutrients Exist in the Soil as Ions Ions are charged particles and can be… positively charged (cations): Ca +2, K +, NH 4 + or negatively charged (anions): Cl -, H 2 PO 4 -, SO 4 -2

4. Ions are either adsorbed or absorbed adsorbed - “like a magnet” absorbed - “like a sponge”

5. Stored (held in reserve) minerals (quartz, feldspar, etc.) organic material soil colloids (clay and humus particles) Readily Available soil solution (ions + water) Nutrient Sources

6. Soil Colloids very small particles (< 1 millionth of a meter) large surface area negative charges along surfaces types of soil colloids: clays, oxides and humus clay humus

7. Soil Colloids Silicate Clays - flat, plate-like crystals arranged in layers - negative surface charge Oxide Clays (sesquioxides) - iron and aluminum based - red in color - common in older soils with hot, humid climates Humus - decomposed organic matter - dark brown to black in color - mostly negative surface charge - high water holding capacity

8. Tetrahedron: Basic building block is 1 silicon atom, connected to 4 oxygen atoms Octahedron: Basic building block is aluminum or magnesium, connected to six hydroxyl groups or oxygen atoms There are many layers in each micelle Typical Clay Structure silica alumina silica

9. Illite

10. - - - - Mg +2 Na + Mg +2 K+K+ Ca +2 - - - - - - - - - - - - - - - Al +3 - - - K+K+ Clay Particle Clay and Organic Particles have Negative Charges Cations are “attracted” and held to these particles with varying degrees of attraction…the order of relative strength of attraction is: Al +3 > H + > Ca +2 > Mg +2 > K + = NH 4 + > Na + NH 4 +

11. CEC - the ability of a soil to hold and release nutrients (cations)

13. Roots Access Nutrients in Solution by… root interception mass flow diffusion