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Unit 6: Soil and Food Resources

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1 Unit 6: Soil and Food Resources
Section 2: Humans and Agriculture

2 Agriculture Arose about 10,000 years ago
Earliest plant and animal domestication occurred in “Fertile Crescent” – Present day Middle East Led to Stationary lifestyle – Establishment of cities and towns Traditional Agriculture – used hand tools and muscle power Also called sustenance or subsistence farming – farmed enough food to survive Many crops grown together (polyculture) Led to Industrial Agriculture – uses large equipment driven by fossil fuels to grow crops for profit Large fields of single crops – monoculture Use pesticides, fertilizer, and irrigation

3 Green Revolution Farming technology was introduced to developing countries Decreased starvation BUT, led to massive soil degradation

4 Soil Degradation When mismanaged, soil use can lead to land degradation Caused by… Deforestation Cropland Overgrazing Degraded soil… Doesn’t hold water as well Is unable to keep high nutrient contents Often erodes faster than other soil This can lead to… Reduced biodiversity Increased desertification Soil salinization Reduced efficiency of food production

5 Soil Erosion Erosion is driven by wind, water, and chemical substances
Flowing water deposits eroded soil when it slows Erosion targets topsoil (most nutrient rich layer) Cover crops can protect soil between plantings

6 The Dust Bowl of the 1930s Following introduction of industrial agriculture, drought occurred and soil eroded in massive dust clouds. Prairie grasses no longer present to keep soil in place due to overgrazing and farming. Lead to economic disaster as farmers abandoned their farms.

7 The Soil Conservation Service pioneered measures to address soil degradation
In response to the Dust Bowl, the U.S. Congress created the Soil Conservation Service Started in 1935, the Service works with farmers to develop conservation plans for individual farms In 1994, the Service was renamed Natural Resources Conservation Service (NRCS) Responsibilities expanded to also include water quality protection and pollution control 1985 Food Security Act (Farm Act): farmers receive a subsidy for taking highly erodible land out of production and replanting it with soil saving plants for years. The 2012 farm bill was never called for a vote in the House of Representatives The future of conservation programs is unclear

8 Farmers protect soil in many ways
Crop rotation = growing different crops from one year to the next Prevents erosion, reduces pests No-till farmers may alternate wheat or corn with nitrogen-fixing soybeans (to increase natural nitrogen in soil) Contour farming = plowing furrows sideways across a hillside Sides of furrows trap water and prevent erosion Terracing = cutting level platforms into steep hillsides The steps of this “staircase” hold water


10 Farmers protect soil in many ways
Intercropping = planting different crops in alternating bands or mixed arrangements Increases ground cover, preventing erosion Replenishes soil Shelterbelts (windbreaks) = rows of trees planted along edges of fields to slow the wind (therefore erosion) Conservation tillage = strategies that reduce the amount of tilling Leaves at least 30% of crop residues in the field (organic matter) No-till farming disturbs the soil even less


12 No-till farming has many benefits


14 Plant cover is the key to erosion control
Farming methods to reduce erosion have one goal—keep the plant cover in place Move livestock to prevent overgrazing Cut select trees in an area rather than clear-cutting Plant vegetation along riverbanks and roadsides China’s huge tree-planting program slows erosion However, the monocultures are not ecologically functioning forests

15 Overgrazing can degrade soil
Grazing animals on rangeland can be sustainable if the total number of grazing animals is kept below the rangeland’s carrying capacity Grazing above carrying capacity leads to degradation Impedes plant regrowth Soil is exposed, allowing erosion, less regrowth, and (positive feedback) more erosion Trampling compacts the soil, preventing water infiltration

16 Irrigation boosts productivity but can damage soils
Irrigation = artificially providing water to support agriculture Unproductive regions become productive farmland 70% of all fresh water used by humans goes to irrigation Irrigation Types: Center-pivot – most effective Gravity flow – uses gravity to release water down sloped ditches Drip irrigation – uses the least amount of water; hoses drip water directly on plants (plants use 90%)


18 Salinization and Waterlogging
Repeated irrigation can reduce crop yields by causing salt buildup in the soil and waterlogging of crop plants. Easier to prevent these than to fix them Irrigate efficiently Filter water

19 Fertilizers boost crop yields but can be overapplied
Organic Fertilizers – animal manure, crop residues, bone meal, and compost (best choices) Inorganic Fertilizers – man-made from chemical compounds Benefits – exact compositions are known; they are soluble & thus immediately available to the plant Costs – quickly leach away; this pollutes the water; doesn’t help the water holding capacity of the soil like organic fertilizers do.


21 Some policies worsen land degradation
Governments spend billions on farm subsides that may be unsustainable Some subsidies support growing water-intensive crops in desert regions Some encourage use of easily degraded land Grazing on federally owned land costs $1.35 per animal unit per month Low cost encourages overgrazing Ranchers are now teaming up with environmental activists to prevent loss of rangeland from development

22 Wetlands have been drained for farming
Wetlands = swamps, marshes, bogs, river floodplains Over 50% have been drained for agriculture in the U.S. Government policy encouraged draining Swamp Lands Acts (1849, 1850, 1860) = drained and converted wetlands to control floods and malaria Wetlands Reserve Program = landowners are paid to protect, restore, and enhance wetlands

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