Chapter 12Chapter 12Soil ResourcesSoil Resources

Soil ProblemsSoil Problems

o Soil ErosionSoil Erosion• Def: wearing away or removal of soil from Def: wearing away or removal of soil from

the land the land • Caused primarily by water and windCaused primarily by water and wind

o Why a problem?Why a problem?• Causes a loss in soil fertility as organic Causes a loss in soil fertility as organic

material and nutrients are erodedmaterial and nutrients are eroded• More fertilizers must be used to replace More fertilizers must be used to replace

nutrients lost to erosionnutrients lost to erosiono Accelerated by poor soil management Accelerated by poor soil management

practicespractices

Three types of soil erosionThree types of soil erosiono Sheet erosion Sheet erosion – water moves down a slope and – water moves down a slope and

erodes topsoil evenlyerodes topsoil evenlyo Rill erosion Rill erosion – cuts shallow channels in the soil– cuts shallow channels in the soilo Gully erosion Gully erosion - is the most severe- cuts deep - is the most severe- cuts deep

channels in the soil. Usually occurs on steep channels in the soil. Usually occurs on steep slopesslopes

o Soil erosion destroys the soil profile, decreasing Soil erosion destroys the soil profile, decreasing the water-holding capacity and increasing the water-holding capacity and increasing compaction. Because water cannot percolate compaction. Because water cannot percolate through, it runs off the land, taking more soil with through, it runs off the land, taking more soil with it. Is this a positive or negative feedback loop?it. Is this a positive or negative feedback loop?

o POSITIVEPOSITIVE

Case in Point: American Case in Point: American Dust BowlDust Bowl

o Great Plains have low Great Plains have low precipitation and subject precipitation and subject to droughtto drought• 1930-1937 severe drought1930-1937 severe drought• No natural vegetation No natural vegetation

roots to hold soil in placeroots to hold soil in place• Replaced by annual cropsReplaced by annual crops

• Winds blew soil as far east Winds blew soil as far east as NYC and DC.as NYC and DC.

• Farmers went bankruptFarmers went bankrupt

Poor agricultural techniques can Poor agricultural techniques can lead to soil erosionlead to soil erosion

o Monoculture cropsMonoculture cropso Row croppingRow croppingo OvergrazingOvergrazingo Improper plowingImproper plowingo Removing crops wastesRemoving crops wastes

o Soil erosion causes damage to Soil erosion causes damage to agriculture, waterways(canals) and agriculture, waterways(canals) and infrastructures (dams)infrastructures (dams)

Soil ProblemsSoil Problemso Nutrient Mineral DepletionNutrient Mineral Depletion

Soil ProblemsSoil Problemso Soil SalinizationSoil Salinization

• The gradual accumulation The gradual accumulation of salt in the soil, usually of salt in the soil, usually due to improper irrigation due to improper irrigation techniquestechniques

• often occurs in arid and often occurs in arid and semiarid regions due to semiarid regions due to the high natural the high natural concentrations of concentrations of inorganic compounds inorganic compounds (mineral salts) in the soil(mineral salts) in the soil

o Salt concentrations get to Salt concentrations get to levels toxic to plantslevels toxic to plants

Soil ProblemsSoil Problems

o DesertificationDesertification• the degradation of once-the degradation of once-

fertile rangeland or forest fertile rangeland or forest into nonproductive desert into nonproductive desert caused partly by soil caused partly by soil erosion, forest removal, erosion, forest removal, overcultivation, and overcultivation, and overgrazingovergrazing

o Change in vegetation Change in vegetation changes climate, further changes climate, further decreasing precipitation decreasing precipitation levelslevels

Soil ConservationSoil Conservationo Conservation TillageConservation Tillage

a method of cultivation in which a method of cultivation in which residues from previous crops are left residues from previous crops are left in the soil, partially covering it and in the soil, partially covering it and helping to hold in place until the helping to hold in place until the newly planted seeds are establishednewly planted seeds are established

Conservation tillage Conservation tillage reduces soil reduces soil erosion, increases organic matter, erosion, increases organic matter, and improves water-holding and improves water-holding capacitycapacity

No-tillage leaves the soil undisturbed in the winter; it saves on fuel costs, machinery wear and tear, and labor time

Crop RotationCrop Rotation

• Planting a series of different Planting a series of different crops in the same field over a crops in the same field over a period of yearsperiod of years

• It lessens insect damage and It lessens insect damage and disease, helps retain essential disease, helps retain essential nutrient minerals, decrease nutrient minerals, decrease erosion, and helps maintains erosion, and helps maintains soil fertilitysoil fertility

Soil ConservationSoil Conservation

o Contour PlowingContour Plowing• Plowing around hill Plowing around hill

instead of up-downinstead of up-down• Decreases soil erosionDecreases soil erosion

o Strip CroppingStrip Cropping• Alternating strips of Alternating strips of

different crops along different crops along natural contoursnatural contours

o TerracingTerracing• Creating terraces on Creating terraces on

steep slopes to prevent steep slopes to prevent erosionerosion

Strip Strip CroppingCropping

TerraciTerracingng

Contour plowing, strip cropping, and terracing help control erosion of farmland with variable topography

Preserving Soil FertilityPreserving Soil Fertilityo Preserving soil fertility can be accomplished Preserving soil fertility can be accomplished

through the use of both organic and through the use of both organic and commercial inorganic fertilizerscommercial inorganic fertilizers

o Organic fertilizersOrganic fertilizers• Animal manure, crop residue, bone meal and compostAnimal manure, crop residue, bone meal and compost• Nutrient available to plants only as material Nutrient available to plants only as material

decomposesdecomposes• Slow acting and long lastingSlow acting and long lasting

o Inorganic fertilizersInorganic fertilizers• Manufactured from chemical compoundsManufactured from chemical compounds• SolubleSoluble

• Fast acting, short lastingFast acting, short lasting• Environmentally sound to limit useEnvironmentally sound to limit use

• Mobile- easily leach and pollute groundwaterMobile- easily leach and pollute groundwater

Soil ReclamationSoil Reclamationo Soil reclamation involves Soil reclamation involves

two steps, stabilizing the two steps, stabilizing the land to prevent further land to prevent further erosion (seeding and erosion (seeding and eventual ground eventual ground cover)and restoring the cover)and restoring the soil to its former fertilitysoil to its former fertility

o ShelterbeltsShelterbelts are one of the are one of the best ways to reduce the best ways to reduce the effects of wind on soil effects of wind on soil erosion (Row of trees erosion (Row of trees planted to reduce wind planted to reduce wind erosion of soil.)erosion of soil.)

oAgroforestryAgroforestry uses both uses both forestry and agricultural forestry and agricultural techniques to improve techniques to improve degraded areas and offer degraded areas and offer economic benefitseconomic benefits

Soil Conservation Policies in USSoil Conservation Policies in US

The Soil Conservation Act of 1935 The Soil Conservation Act of 1935 authorized the formation of the Soil authorized the formation of the Soil Conservation Service (now the NRCS); Conservation Service (now the NRCS); Mandates the protection of the nation’s Mandates the protection of the nation’s soil reserves. Deals with erosion, carries soil reserves. Deals with erosion, carries out soil survey and does research on soil out soil survey and does research on soil salinity.salinity.

o Food Security Act (Farm Bill) 1985Food Security Act (Farm Bill) 1985• contained provisions for two main soil contained provisions for two main soil

conservation programsconservation programs– Conservation Compliance ProgramConservation Compliance Program– Conservation Reserve Program (CRP)Conservation Reserve Program (CRP)

Just some factoidsJust some factoids

o Soil on cultivated land in the USA is Soil on cultivated land in the USA is eroding 16x faster than it can form.eroding 16x faster than it can form.

o More soil is lost each year in the US than More soil is lost each year in the US than during the dust bowl due to soil erosion.during the dust bowl due to soil erosion.

o 15% of all land on Earth (mostly in 15% of all land on Earth (mostly in Africa/Asia) is no longer available to grow Africa/Asia) is no longer available to grow crops due to overgrazing (35%) crops due to overgrazing (35%) deforestation(30%) and unsustainable deforestation(30%) and unsustainable farming (28%).farming (28%).