1. Why is a study of soil important? 90% of the world’s food comes from land- based agriculture. Maintenance of soil is the cornerstone of sustainable civilizations. Simply stated, it is the “foundation” of terrestrial life.

2. Global Trend: Where Did All the Farms Go? 22% global land for crops grazing and forestry are degraded; reduced potential productivity. Poor farming practices = loss of soils and farmland. –Erosion –Salinization Development in United States = loss of 1.4 million acres of farmland per year.

3. Topsoil Formation

4. Soil Profile Not all soil under your feet is the same. Soil becomes more mineral and rocky with depth as organic input is at the surface and weathering of bedrock (parent material) at depth. Nutrient content often decreases with depth

5. Soil Texture Soil texture refers to the percentage of each type of particle found in the soil. –Loam soil is approximately 40% sand, 40% silt, and 20% clay. Sand (large) 2 - 0.02 mm Silt (small) 0.02 – 0.002 mm Clay (smaller) < 0.002 mm

6. Soil Texture Classification Feel Your Soil Assignment #7 Draw three lines as follows: 1)From %clay value run line parallel to %sand. 2)From %silt value run line parallel to %clay. 3)From %sand value run line parallel to %silt E.g. Sandy Clay Loam: 25% clay 25% clay 15% silt 15% silt 60% sand 60% sand

7. Soil Texture and Properties TextureWater Infiltration Water- holding Capacity Nutrient- holding Capacity Aeration SandGoodPoor Good SiltMedium ClayPoorGood Poor OrganicMediumGood Medium LoamMedium

8. Soil Classes Mollisols: fertile soils with deep A horizon; best agriculture soils Oxisols: iron and aluminum oxides in B horizon; little O horizon; Poor agriculture soils Alfisols: well-developed O, A, E, and B horizons; suitable for agriculture if supplemented Aridisols: little vertical structure; thin and unsuitable for sustainable agriculture

9. Plant-soil-water Relationships Plants need water for photosynthesis, cell function, and turgor pressure so not to wilt. Water return to the atmosphere is slower by transpiration than direct evaporation from bare mineral soil.

10. Plant-soil-water Relationships

11. Productive Soil Good supply of nutrients and nutrient-holding capacity Infiltration, good water-holding capacity, resists evaporative water loss Porous structure for aeration Near-neutral pH Low salt content Moderate organic content Active Detritus Food Web

12. Soil: IT’S ALIVE!