Soil

1. Soil • This section is in addition to Chapter 3

2. Soil • Produced slowly (200-1000 years typically) by weathering of rock, deposition of sediments, and decomposition of organic matter • Soil horizons – separate zones within soil • Soil profile – cross-section view of soil

3. Horizons • O horizon – surface litter • A horizon – top soil, made up of inorganic particles (clay, silt, sand) and humus (organic particles from decomposed organisms) • Dark topsoil is richer in nutrients • Releases water and nutrients slowly • Provides aeration to roots • Healthy soil contains many nematodes and bacteria, fungi, etc.

4. Lords and ladies Oaktree Word sorrel Dog violet Organic debris Builds up Earthworm Grasses and small shrubs Rock fragments Millipede Mole Moss and lichen Fern Honey fungus O horizon Leaf litter A horizon Topsoil Bedrock B horizon Subsoil Immature soil Regolith Young soil Pseudoscorpion C horizon Parent material Mite Nematode Actinomycetes Root system Red earth mite Fungus Springtail Mature soil Bacteria Fig. 10.12, p. 220

5. Poor topsoil • Grey, yellow and red are not the colors of healthy topsoil • Generally means that soil is lacking nutrients • Best soil is called loam with equal parts sand, silt, clay and humus • Leaching – dissolving and carrying nutrients (or pollutants) through soil into lower layers

6. B – horizon and C - horizon • B – Subsoil mostly broken down rock with little organic matter • C- parent material broken down rock on top of the bedrock

7. Soils • Texture – relative amount of different sized particles present (sand, silt, clay) • Porosity – volume of pore space in the soil • Permeability – the ability of water to flow through the soil

8. Water Water High permeability Low permeability Sandy soil Clay soil

9. Soils • Clay – high porosity, low permeability • Sand – high permeability, low porosity • Acidity is another factor • Where rain is low, calcium and other alkaline compounds may build up (sulfur can be added – turns to sulfuric acid by bacteria)

10. Forest litter leaf mold Acid litter and humus Acidic light- colored humus Humus-mineral mixture Light-colored and acidic Light, grayish- brown, silt loam Iron and aluminum compounds mixed with clay Dark brown Firm clay Humus and iron and aluminum compounds Tropical Rain Forest Soil (humid, tropical climate) Deciduous Forest Soil (humid, mild climate) Coniferous Forest Soil (humid, cold climate) Fig. 10.15b, p. 223

11. Mosaic of closely packed pebbles, boulders Alkaline, dark, and rich in humus Weak humus- mineral mixture Dry, brown to reddish-brown with variable accumulations of clay, calcium carbonate, and soluble salts Clay, calcium compounds Desert Soil (hot, dry climate) Grassland Soil (semiarid climate) Fig. 10.15a, p. 223

12. Soil erosion • Causes – mainly water and wind • Human induced causes – farming, logging, mining, construction, overgrazing by livestock, off-road vehicles, burning, and more (go us!)

13. Soil erosion • Types • Sheet • Uniform loss of soil, usually when water crosses a flat field • Rill • Fast flowing water cuts small rivulets in soil • Gully • Rivulets join to become larger, channel becomes wider and deeper, usually on steeper slopes or where water moves fast

14. Global soil loss • This is a major problem world wide • Have lost about 15% of land for agriculture to soil erosion • Overgrazing • Deforestation • Unsustainable farming • Also 40% of ag land is seriously degraded due to soil erosion, salinization, water logging and compaction

15. Moderate Severe Very Severe Fig. 10.21, p. 228 Desertification of arid and semiarid lands

16. Areas of serious concern Areas of some concern Stable or nonvegetative areas Global soil erosion Fig. 10.19, p. 226

17. Desertification • Turning productive (fertile) soil into less productive soil (10% loss or more) • Overgrazing • Deforestation • Surface mining • Poor irrigation techniques • Poor farming techniques • Soil compaction

18. Salinization • As water flows over the land, salts are leached out • When water irrigates a field it is left to evaporate typically • This repeated process causes the dissolved salts to accumulate and possibly severely reduce plant productivity • Fields must be repeatedly flushed with fresh water to remove salt build up

19. Waterlogging • When fields are irrigated they allow water to sink into the soil. • Winds can dry the surface • As more water is applied the root area of plants is over saturated reducing yield • As clay is brought to subsoil levels it can act as a boundary for water infiltration

20. Evaporation Transpiration Evaporation Evaporation Waterlogging Less permeable clay layer Fig. 10.22, p. 229

21. Soil conservation • Conservation tillage – (no till farming) disturb the soil as little as possible • Reducing erosion also helps – save fuel, cut costs, hold water, avoid compaction, allow more crops to be grown, increase yields, reduce release of carbon dioxide

22. Soil conservation • Terracing – making flat growing areas on hillsides • Contour farming – planting crops perpendicular to the hill slope, not parallel • Strip cropping – planting alternating rows of crops to replace lost soil nutrients (legumes) • Alley cropping – planting crops between rows of trees

23. Control planting and strip cropping Fig. 10.24b, p. 230

24. Alley cropping Fig. 10.24c, p. 230

25. Fig. 10.24a, p. 230 Terracing

26. Soil conservation • Gully reclamation – seeding with fast growing native grasses, slows erosion or “reverses” it • Also building small dams traps sediments • Building channels to divert water or slow water • Windbreaks – trees planted around open land to prevent erosion • Retains soil moisture (shade, less wind) • Habitats for birds, bees, etc. • Land classification – identify marginal land that should not be farmed

27. Windbreaks Fig. 10.24d, p. 230

28. Soil fertility • Inorganic fertilizers – easily transported, stored, and applied • Do not add humus – less water and air holding ability, leads to compaction • Only supply about 3 of 20 needed nutrients • Requires large amount of energy for production • Releases nitrous oxide (N2O) during production, a green house gas

29. Soil fertility • Organic fertilizers – the odor is a problem • Animal manure – difficult to collect and transfer easily, hard to store • Green manure – compost, aerates soil, improves water retention, recycles nutrients • Crop rotation – allows nutrients to return to soil, otherwise same crop continually strips same nutrient, keeps yields high, reduces erosion