Components of Soil Humus: partially decomposed organic matter (a carbon sink)

1. Components of Soil Humus: partially decomposed organic matter (a carbon sink) Dark brown or black color indicates high nitrogen content.

2. Inorganic Soil Components: Particle Size: Clay- Very fine Silt- Fine Sand- Medium Gravel- Large

3. Discuss with your table partner: Some important characteristics of soil are how well the soil • allows water to infiltrate (permeability) • holds water • holds nutrients • allow for aeration of the soil Why is aeration one of the important characteristics of soil? The cells in plant roots need to perform cellular respiration to obtain energy.

4. Discuss with your table partner: • How would the pore spaces in clay soil compare to the pore spaces in sandy soil? • How would the different pore spaces affect each of these soil types ability to: • Allow water to infiltrate • Hold water • Allow air to infiltrate • Hold nutrients Fill in the next two slides with your answers.

5. Soil Porosity Micropores : allow for attractive forces that retain water. • Clay and silty soils form more micropores. Macropores: allow for better water infiltration and air spaces. • Sandy soils form more macropores http://techalive.mtu.edu/meec/module06/Permeability.htm

7. Video: Fine particle soil

8. Discuss with your table partner: What is the relationship between with water (and air) infiltrating capacity of a soil and its water-holding capacity? The ability of a soil to allow water to infiltrate is inversely related to it ability to retain water. Soils that can best balance these competing demands of the plants are generally best suited for plant growth.

9. Loams: Roughly equal mixture of clay, silt, and sand. Mixture of pore sizes to balance water retention and aeration.

10. Discuss with your table partner: Use the soil triangle to determine the soil sample type from the percentages shown. 20% sand 45 % silt 35 % clay clay loam/silty clay loam

11. Soil Video http://www.youtube.com/watch?v=knrmCbctGEA

12. Soil Layers O horizon- leaf litter and humus A horizon- topsoil Anchored by vegetation E horizon- leached nutrients B horizon- parent material contains most of soil’s inorganic material

13. Typical Soil Profiles in Different Biomes

14. Typical Soil Profiles in Different Biomes

15. While soil is a potentially renewable resource, it takes long periods of time to form topsoil, typically 200–1000 years to form 2.5 centimeters (1 inch) of topsoil; • Topsoil is eroding faster than it forms in about one–third of the world's cropland. Soil Erosion

16. Conventional Tillage Conventional tillage leaves the soil loose and uncovered which can lead to erosion. Tilling Disk Harrow

17. Soil conservation: reducing erosion conservation–tillage farming minimizes soil disturbance. • use of special tillers which loosen subsurface soil without turning over top soil • no–till methods that inject seeds, fertilizers, & herbicides in unplowed soil • maintaining a layer of crop residue (on 30 % or more of the field) reduces water erosion. Crop residue

18. Discuss with our table partner: Review the difference between conventional tillage and conservation tillage. Conventional tillage is referring to traditional methods of plowing/ overturning the soil. Conservation tillage is a method to reduce soil erosion (save soil) by reducing the disruption of the soil.

19. Desertification of arid & semiarid lands results when land productivity drops markedly. Causes: • overgrazing • deforestation & devegetation • poor irrigation techniques; • salt buildup • soil compaction by farm machinery.

20. Discuss with your table partner: Salinization: salt build-up in irrigated soil to levels that decrease crop yields. Why does salinization occur? Why does it only occur for irrigated fields? Occurs because irrigation water (unlike rain) contains some salts which increases in concentration as evaporation of water leaves behind salt.

21. Discuss with your table partner: Waterlogging results when excess irrigation water raises the water table (level of the water below the soil surface) & lowers crop productivity. Why would waterlogging reduce crop productivity? Prevents the aeration of the roots.

22. Soil Conservation Terracing protects steep slopes, retains water for crops at each level and reduces erosion by controlling runoff. Contour farming follows natural land contours. Each row of crops acts as a dam to slow water runoff.

23. Soil Conservation • wind breaks uses trees between fields to slow wind erosion • strip cropping uses strips of different plants in between crops to slow erosion

24. Discuss with your table partner: Another strategy to improve soil fertility is crop rotation. What type of crops might be grown in alternating years that would improve the nutrient levels of the soil? Legumes (beans, peas, alfalfa, clover) because they have root nodules that hold nitrogen-fixing bacteria) Besides improving soil fertility, crop rotation can also reduce pest levels. Why might this be the case? May reduce the population of pests that specialize on a particular crop such as the corn borer.