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

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1 Components of Soil Humus: (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 o allows water to infiltrate (permeability) o holds water oholds nutrients oallow for aeration of the soil Why is aeration one of the important characteristics of soil?

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. soils form more micropores. Macropores allow for. soils form more macropores

6 Soil Texture Water- Infiltrating Capacity Water- Holding Capacity Aeration Nutrient- Holding Capacity Clay Silt Medium Medium Medium Medium Sand Loam (even mix of particle sizes) Medium Medium Medium Medium

7 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 related to it ability to retain water. Soil Permeability le06/permeability.htm

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

9 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

10 Soil Video

11 Soil Layers O horizon- A horizon- topsoil Anchored by vegetation E horizon- B horizon- parent material contains most of soil s inorganic material

12 Typical Soil Profiles in Different Biomes

13 Typical Soil Profiles in Different Biomes

14 Soil Erosion While soil is a potentially renewable resource, it takes long periods of time to form topsoil, typically years to form Topsoil is eroding faster than it forms in about one third of the world's cropland.

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

16 Soil conservation: reducing erosion conservation tillage farming minimizes soil disturbance. use of special tillers which loosen subsurface soil without turning over top soil methods that inject seeds, fertilizers, & herbicides in unplowed soil maintaining a layer of (on 30 % or more of the field) reduces water Crop residue

17 Discuss with our table partner: Review the difference between conventional tillage and conservation tillage.

18 Desertification of arid & semiarid lands results when land productivity drops markedly. Causes: overgrazing deforestation & devegetation poor irrigation techniques; salt buildup

19 Discuss with your table partner: Salinization: salt build-up in irrigated lands to levels that decrease crop yields. Why does salinization occur?

20 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?

21 Soil Conservation Terracing protects, 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.

22 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

23 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? Besides improving soil fertility, crop rotation can also reduce pest levels. Why might this be the case?