Soil components

1. Soil components Average:

3. Weathering - breakdown of rocks at the Earth’s surface • 3 types: • Physical • (mechanical) • Chemical • Biological

5. Immature soil O horizon Leaf litter A horizon Topsoil Regolith B horizon Subsoil Bedrock C horizon Parent material Young soil Mature soil Fig. 10.12, p. 220

6. Soil Profile – cross section of horizons O Horizon – organic, leaf litter A Horizon - plant roots grow in this dark-colored layer. humus & mineral particles.E Horizon - eluviation (leaching) layer B Horizon – subsoil, clay and mineral leachate C Horizon or regolith, weathered parent materialR Horizon - The unweathered rock (bedrock) layer that is beneath all the other layers.

7. Soils vary by region

8. Most productive agricultural soils

9. Soil Properties • Texture • Porosity • Structure • Permeability • Cation exchange capacity • Nutrient Content • pH

10. Soil Texture Classification

11. Soil Quality Texture Nutrient Infiltration Water-Holding Aeration Tilth Capacity Capacity Clay Good Poor Good Poor Poor Silt Medium Medium Medium Medium Medium Sand Poor Good Poor Good Good Loam Medium Medium Medium Medium Medium Fig. 10.15b, p. 223

12. Porosity - % pore space Finer particles – lower porosity, low oxygen and water infiltration Larger particles – water passes too quickly Best for agriculture: mixed loam

13. Capillary Action • Capillary water • Capillary action (capillarity) can pull water upwards against gravity • Smaller spaces = more capillary action ~Ex. clay

14. Soil Structure

15. Cation exchange = • Negatively charged soils hold cations: Ca +2, Mg+2, K+ • Cation exchange capacity = a soil’s ability to hold cations – reducing leaching • A useful measure of soil fertility • Greatest in fine soils www.uwsp.edu

17. Primary Plant Nutrients • Nitrogen (N): most important nutrient besides water; determines rate of growth • deficiency symptom: yellowing of leaves • Phosphorous (P): required during germination and fruit/seed formation • Deficiency symptoms: stunted growth; purple-colored leaves • Potassium (K): regulatory • Deficiency symptoms: stunted growth; mottled leaves

18. Justus von Liebig’s Law of Minimum Plant production can be no greater than that level allowed by the growth factor present in the lowest amount relative to the optimum amount for that factor

19. Soil Degradation

20. Soil Degradation by Agriculture

21. Soil erosion Splash Sheet Rill Gully

22. Desertification • Desertification = a loss of more than 10% productivity • Erosion, soil compaction, forest removal, overgrazing, salinization, climate change, depletion of water sources • Most prone areas = arid and semiarid lands

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26. Protecting soil: crop rotation and contour farming • Crop Rotation = alternating the crops grown field from one season or year to the next, • Cover crops protect soil when main crops aren’t planted • Wheat or corn and soybeans • Contour Farming = plowing furrows sideways across a hillside, perpendicular to its slope, to prevent rills and gullies

27. Protecting soil: shelterbelts and reduced tillage • Shelterbelts or Windbreaks = rows of trees or other tall, perennial plants that are planted along the edges of fields to slow the wind • Alley cropping = shelterbelts + intercropping • Reduced Tillage = furrows are cut in the soil, a seed is dropped in and the furrow is closed • No-till farming disturbs the soil even less

28. Plant cover reduces erosion • Eroding banks along creeks and roadsides are stabilized by planting plants to anchor soil • China has the world’s largest tree-planting program • It does slow erosion • But it does not create ecologically functional forests, because monocultures are planted

29. Salinization prevention • It is easier and cheaper to prevent salinization than fix it • Do not plant water-guzzling crops in sensitive areas • Irrigate with low-salt water • Irrigate efficiently, supplying only water that the crop requires • Drip irrigation targets water directly to plants

30. Fertilizers boost yields but cause problems • Fertilizer = substances that contain essential nutrients • Inorganic fertilizers = mined or synthetically manufactured mineral supplements • Organic fertilizers = the remains or wastes of organisms • manure, crop residues, fresh vegetation • Compost = produced when decomposers break down organic matter Applying synthetic fertilizer, vs. Planting rye, a “green manure”

31. Overapplication of Fertilizer • Inorganic fertilizer use has skyrocketed • Overapplying fertilizer can ruin the soil and severely pollute several areas • Runoff causes eutrophication in nearby water systems • Nitrates leach through soil and contaminate groundwater • Nitrates can also volatilize (evaporate) into the air

32. Environmental effects of over-fertilizing

33. Effects of overgrazing • Non-native invasive species invade • Less palatable to livestock • Out compete native vegetation Ungrazed plot Grazed plot

34. Forestry impacts soil • Clear-cutting = the removal of all trees from an area at once • Leads to soil erosion, especially on steep slopes