Soil Degradation and Conservation

1. Soil Degradation and Conservation Soil Degradation – the reduction in the quality and usefulness of soil Soil Conservation – maintaining and/or restoring soil to optimal quality

2. Agriculture today We have converted 38% of Earth’s surface for agriculture, the practice of cultivating soil, producing crops, and raising livestock for human use and consumption. Croplands (for growing plant crops) and rangelands (for grazing animal livestock) depend on healthy soil.

3. Natural Capital Croplands Croplands Ecological Services Economic Services Ecological Services Economic Services • Help maintain water flow and • soil infiltration • Provide partial erosion protection • Can build soil organic matter • Store atmospheric carbon • Provide wildlife habitat for some • species • Food crops • Fiber crops • Crop genetic • resources • Jobs • Help maintain water flow and soil infiltration • Provide partial erosion protection • Can build soil organic matter • Store atmospheric carbon • Provide wildlife habitat for some species • Food crops • Fiber crops • Crop genetic resources • Jobs

4. World soil conditions • Soils are becoming degraded in many regions. Figure 8.1a

5. Soil degradation by continent • Europe’s land is most degraded because of its long history of intensive agriculture. • But Asia’s and Africa’s soils are fast becoming degraded. Figure 8.1b

6. Causes of soil degradation • Most soil degradation is caused by: • • livestock overgrazing • • deforestation • • cropland agriculture. Figure 8.2

7. The Importance of Humus • AKA – Organic Matter • Dark, crumbly mass of undifferentiated material made up of complex organic compounds • Soils with high humus content • hold moisture better and • are more productive for plant life.

8. Soil characterization • Soil can be characterized by color and several other traits: • Texture (percentage sand, silt, clay) • Structure • Porosity • Cation exchange capacity – the ability of clay and humus particles to attract K, Mg, Ca, Fe, and other metal minerals necessary for plant growth • pH • Parent Material • Infiltration rate / Permeability • Nutrient concentrations • Best for plant growth is loam, an even mix of sand, silt and clay.

9. Erosion and deposition • Erosion = removal of material from one place and its transport elsewhere by wind or water • Deposition = arrival of eroded material at a new location • These processes are natural, and can build up fertile soil. • But where artificially sped up, they are a big problem for farming.

10. Erosion • Commonly caused by: • • Overcultivating, too much plowing, poor planning • • Overgrazing rangeland with livestock • • Deforestation, especially on slopes

11. Types of soil erosion Splash erosion Rill erosion Gully erosion Sheet erosion Figure 8.11

12. Erosion: A global problem • Over 19 billion ha (47 billion acres) suffer from erosion or other soil degradation. • Much of the erosion ends up in the water shed • Mississippi River…to thin to plow to thick to drink (Sam Clemens) • Soil integrity and fertility is reduced.

13. Desertification • A loss of more than 10% productivity due to: • • Erosion • • Soil compaction • • Forest removal • • Overgrazing • • Drought • • Salinization • • Climate change • • Depletion of water resources When severe, there is expansion of desert areas, or creation of new ones, e.g., the Middle East, formerly, “Fertile Crescent”.

14. The Dust Bowl • Drought and degraded farmland produced the 1930s Dust Bowl. • Storms brought dust from the U.S. Great Plains all the way to New York and Washington, and wrecked many lives. Figure 8.14

15. Kansas Colorado Dust Bowl Oklahoma New Mexico Texas MEXICO

16. Consequences Causes Overgrazing Deforestation Erosion Salinization Soil compaction Natural climate change Worsening drought Famine Economic losses Lower living standards Environmental refugees

17. Soil conservation • As a result of the Dust Bowl, • the U.S. Soil Conservation Act of 1935 and • the Soil Conservation Service (SCS) were created. • SCS: Local agents in conservation districts worked with farmers to disseminate scientific knowledge and help them conserve their soil.

18. Preventing soil degradation • Several farming strategies to prevent soil degradation: • • Crop rotation • • Contour farming • • Intercropping • • Terracing • • Shelterbelts • • Conservation tillage

19. Crop rotation • Alternating the crop planted (e.g., between corn and soybeans) can restore nutrients to soil and fight pests and disease. Figure 8.16a

20. Contour farming • Planting along contour lines of slopes helps reduce erosion on hillsides. Figure 8.16b

21. Intercropping • Mixing crops such as in strip cropping can provide nutrients and reduce erosion. Figure 8.16c

22. (c) Alley cropping

23. Terracing • Cutting stairsteps or terraces is the only way to farm extremely steep hillsides without causing massive erosion. It is labor-intensive to create, but has been a mainstay for centuries in the Himalayas and the Andes. Figure 8.16d

24. Shelterbelts • Rows of fast-growing trees around crop plantings provide windbreaks, reducing erosion by wind. Figure 8.16e

25. Conservation tillage • No-till and reduced-tillage farming leaves old crop residue on the ground instead of plowing it into soil. This covers the soil, keeping it in place. • Here, corn grows up out of a “cover crop.” Figure 8.16f

26. Conservation Tillage Advantages • Reduces erosion • Increases humus • Saves fuel • Reduces carbon dioxide emissions • Reduces irrigation because soil holds water • Reduces soil compaction • Allows for several crops per season • High crop yield

27. Conservation tillage • Issues with Conservation tillage • More chemical herbicides (because weeds are not plowed under) • More fertilizer (because other plants compete with crops for nutrients) • Fungal growth due to soil moisture • Breeding ground for pest insects and rodents • Expensive new equipment • Time and cost to train farmers • Legume cover crops can keep weeds at bay while nourishing soil, and green manures can be used as organic fertilizers.

28. Soil Enhancement • Crop rotation • Addition of aeration organisms such as earthworms • Addition of compost, manure, other organic matter - • Mulch on top of soil

29. Irrigation • The artificial provision of water to support agriculture • 70% of all freshwater used by humans is used for irrigation. • Irrigated land globally covers more area than all of Mexico and Central America combined. • Irrigation has boosted productivity in many places … but too much can cause problems.

30. Waterlogging and salinization • Overirrigation can raise the water table high enough to suffocate plant roots with waterlogging. • Salinization (buildup of salts in surface soil layers) is a more widespread problem. • Evaporation in arid areas draws water up through the soil, bringing salts with it. Irrigation causes repeated evaporation, bringing more salts up.

31. Improved irrigation • In conventional irrigation, only 40% of the water reaches plants. • Efficient drip irrigation targeted to plants conserves water, saves money, and reduces problems like salinization. Figure 8.17

32. Solutions Soil Salinization Prevention Cleanup Flushing soil (expensive and wastes water) Not growing crops for 2-5 years Installing under- ground drainage systems (expensive) Reduce irrigation Switch to salt- tolerant crops (such as barley, cotton, sugar beet)

33. Fertilizers • Supply nutrients to crops • Inorganic fertilizers = mined or synthetically manufactured mineral supplements • Organic fertilizers = animal manure, crop residues, compost, etc. Figure 8.18

34. Global fertilizer usages • Fertilizer use has risen dramatically in the past 50 years. Figure 8.19b

35. Trade-Offs Inorganic Commercial Fertilizers Disadvantages Advantages Easy to transport Easy to store Easy to apply Inexpensive to produce Help feed one of every three people in the world Without commercial inorganic fertilizers, world food output could drop by 40% Do not add humus to soil Reduce organic matter in soil Reduce ability of soil to hold water Lower oxygen content of soil Require large amounts of energy to produce, transport, and apply Release the greenhouse gas nitrous oxide (N2O) Runoff can overfertilize nearby lakes and kill fish

36. Overgrazing • When livestock eat too much plant cover on rangelands, impeding plant regrowth • The contrast between ungrazed and overgrazed land on either side of a fenceline can be striking. • Overgrazing reduced by using paddocks – grazing rotation Figure 8.22

37. Overgrazing • Overgrazing can set in motion a series of positive feedback loops. Figure 8.21

38. Recent soil conservation laws • The U.S. has continued to pass soil conservation legislation in recent years: • • Food Security Act of 1985 • • Conservation Reserve Program, 1985 • • Freedom to Farm Act, 1996 • • Low-Input Sustainable Agriculture Program, 1998 • Internationally, there is the UN’s “FAR” program in Asia.