Chapter 8: Soil

Part 3

Erosion• Erosion: the process of soil and humus particles

being picked up and ___________ away by water and wind– Occurs any time soil is bared and ___________

• Soil removal may be _______ and gradual (e.g., by wind) or ___________ (e.g., gullies formed by a single storm)

• _____________ cover prevents erosion from water– Reducing the ____________ of raindrops– Allowing slow _____________

• Grass is excellent for erosion ____________• Vegetation also slows wind _______________

Splash, sheet, and gully erosion• __________ erosion: begins the process of erosion– Raindrops _______ up the clumpy structure of topsoil– Dislodged particles wash ________ other aggregates– ____________ infiltration and aeration

• _________ erosion: the result of decreased infiltration– More water ____ ____, carrying away fine particles

• Gully erosion: water __________ into rivulets and streams– Water’s greater volume, velocity, energy remove soil

• Once started, erosion can turn into a vicious cycle– Less vegetation exposes soil to more erosion

Desert pavement• Another devastating feature of wind and water

erosion: ________________removal of soil particles– ______ humus and clay are the first to be carried away– Rocks, stones, coarse sand ____________– The remaining soil becomes _____________

• Deserts are sandy because ________ removes fine material

• Desert pavement: occurs in some deserts– Removal of fine material leaves a thin surface ______ of

stones and gravel– This protective layer is easily _____________ (e.g., by

vehicles)

Formation of desert pavement

Cryptogamic crusts• ____________ erosion can change soil composition– Rainfall clogs soil– Soil ____________ when it dries– Cryptograms (algae, ____________, mosses) grow

• Growth of these __________ causes a cryptogamic crust– It ________________s soil– It adds nutrients through nitrogen ___________– It can __________ infiltration and seed germination

• These crusts are easily broken up by __________, etc.– Loosened soil is subject to wind and water erosion

Drylands and desertification• Clay and humus are the most _______ parts of soil– For nutrient- and water-holding capacity– Their removal results in nutrients being removed

• Regions with _______ rainfall or long dry seasons support grasses, scrub trees, and crops only if soils have good water- and nutrient-_________ capacity– Erosion causes these areas to become deserts

• Desertification: a __________ reduction in the productivity of arid, semiarid, and seasonally dry areas (drylands)– Does not mean advancing deserts

Drylands• Desertification is a process of land ___________– Due to droughts, overgrazing, erosion, deforestation,

_____________________– It is extremely serious because it is ____________

• Dryland ecosystems cover 41% of Earth’s surface– They are defined by ____________, not temperature– They receive minimal rainfall– Droughts are __________ —they can last for years

• Rainfall causes vegetation to ________ so drylands are not desertified

Drylands in danger• 10–20% of drylands suffer some form of degradation– Inhabited by some of the world’s _____________

• The UN Convention to Combat Desertification (______________)– Addresses funding projects to _______ degradation– “_____________” programs so people can help

themselves– Gathering and dissemination of ___________ knowledge

• TerrAfrica: UNCCD alliance to coordinate efforts to arrest degradation and promote sustainable management

• __________ pose the greatest threat to dryland ecosystems

Causes of erosion: overcultivation• Plowing to grow crops ___________ soil to wind

and water erosion– Soil remains _____ before planting and after harvest

• Plowing causes ____________ erosion – Destroying soil’s aggregate ___________– Decreasing aeration and infiltration

• Tractors _____________ soil– Reducing aeration and infiltration– Increasing ____________ water loss and humus

oxidation• ____________ cash crops with hay and clover is

sustainable

No-till planting• __________ agriculture: a technique allowing

continuous cropping while minimizing erosion– Routinely practiced in the ________.

• After spraying a field with __________ to kill weeds– A planting apparatus cuts a _________ through the mulch– Drops ____________ and fertilizer– Closes the furrow

• The waste from the previous crop becomes ______– So the soil is never ________________

• Low-till farming uses _______ pass (not 6–12) over a field

Inorganic fertilizer• Can provide optimal amounts of nutrients ________– But it lacks ________ matter to support organisms and

build soil structure• It can keep nutrient content high under _________

cultivation (two or more cash crops/year) – But ______________ and soil degradation proceed– Additional fertilizer _____________ into waterways

• Chemical fertilizers have a valuable ___________ in agriculture– Organic fertilizers may not have enough __________

• Growers must use each fertilizer as necessary

Reducing soil erosion• ___________ __________cropping: plowing and cultivating

at right angles to contour slopes– ____________: protective belts of trees and shrubs planted

along plowed fields• The U.S. Natural Resource Conservation Service (NRCS)– Established in response to the _________ _________– Regional offices provide information to farmers and others

regarding soil and water conservation _______• U.S. soil erosion has decreased through conservation– Windbreaks, grassed waterways, ___________ to filter runoff

Overgrazing• Livestock __________ on grasslands and cleared

forest slopes– 65% of drylands are grasslands

• Land is often overgrazed– _____________ land is eroded and degraded

• In the 1800s American buffalo (bison) were slaughtered– Rangelands stocked with ________ were overgrazed– Leading to erosion and growth of ___________ plants

• U.S. western rangelands produce less than _____of the forage they produced before commercial grazing– Yet 20% of rangelands remain ______________

Degraded rangelands

• The National Public Lands Grazing Campaign documents ________ effects of livestock grazing – Competition of livestock with _____ animals for food– One-third of ____________ species are in danger due to

cattle-raising practices (predator control, fire suppression)– Wooded zones along streams are __________ and

polluted– _________ streams make fish species the fastest-

disappearing wildlife group• Desertification impacts 85% of North America’s

drylands– The most widespread cause is livestock _________

Public lands

• Overgrazing occurs because rangelands are public lands– ___________of the ___________: the incentive is for all to

keep grazing, even though the range is being overgrazed• The U.S. Bureau of Land Management (____) and

Forest Service leases grazing rights on 2 million km2 of land– Federal land is owned by ______________– Animal unit = one cow-calf pair or _______ sheep– The grazing fee ($1.35/animal unit/month) is ______ what

would be paid on private land

Why are rangelands overgrazed?• The 1934 Taylor Grazing Act prohibits reducing

grazing levels or keeps grazing fees below ______ level– The U.S. government lost ______ million in 2004– $500 million more was lost in ecological ______ (to

watersheds, streams, wildlife, endangered species)

• When Congress and the BLM try to raise fees, western congressmen threaten to cut the BLM ___________

Irrigation• Irrigation: supplying water to croplands _________– Dramatically increases ______________– Is a ___________ contributor to land degradation

• Flood irrigation: river water flows into canals to ______________ fields

• Center-pivot irrigation: water is pumped from a well into a giant pivoting _______________

• The U.S. Bureau of Reclamation is involved with supplying irrigation water to the western ________– Irrigating 4 million hectares (10 million acres)

• Worldwide irrigation is huge and is still _________

Salinization

• Salinization: the accumulation of _______ in and on the soil– Suppresses plant growth

• Even the ________ irrigation water has some salt– Watering dryland soils ________ minerals in the soil– ____________ or transpiration leaves salts behind

• Salinization is considered a form of ____________– ____ million hectares (3.7 million acres) are lost each year

to salinization and waterlogging– 160,000 hectares (___________ acres) in California are

unproductive, costing $30 million/year

Salinization can be avoided or reversed• Enough water must be used to ________ salts

downward– Insufficient _________ results in waterlogged soils– Installing drainage pipes is ____________

• Kesterson National Wildlife Refuge received drainage from ____________-enriched soils– ___________ birds, fish, insects, and plants– It was declared a ___________ waste dump– It has been drained and capped with __________

• Over 14 other U.S. locations have toxic irrigation water– The “Kesterson Effect”

Soil conservation• Healthy soils are essential for agricultural

production– _______ activities (overcultivation, overgrazing,

deforestation) cause erosion

• Sustainability means doing all we can to reduce erosion

• Soil conservation must be practiced at two levels– ________ landholders can best preserve soil through

traditional knowledge and practices– _________ policies can lead to conservation or disaster

Helping individual landholders• Individual landholders, farmers, and herders hold the

key to sustainable soil stewardship• They must be convinced that conservation will work– That it is _______ and will help them in the ____ ___

• Small, realistic steps must be taken– ______________, advice, and encouragement

• Sustainable Agriculture and Rural Development Initiative (SARD) coordinates efforts to reach small farmers– _____________organize and adopt sustainable practices– These practices can be used in other similar situations

The Keita Project• Niger is one of the ________ countries in the world– Part is in the Sahel, a _____________ grassland

• In 1982 the Italian government started an ______________ project in the Keita district, which has 230,000 people– _______ were built to catch summer rains– 18 million trees were planted– Rock dams stopped _______ erosion– Local people (especially __________) worked

• The Keita district is now a flourishing place for crops– Desertification has been halted

Land in the Keita district of Niger

Two paradigms

• Desertification is happening in many areas– Leading to permanent damage, poverty, and misery– Human factors: population growth, immigration,

_______ land tenure, cash crops– Erosion from overgrazing and overcultivation is made

worse by drought and __________ change• Desertification is not inevitable: another option is

to recognize degradation and take corrective measures– Better management, soil and water conservation,

diversifying income to relieve pressure on the land

Public policy and soils• Original U.S. farm policy: increasing __________– This goal was achieved

• The federal government supports agriculture through ___________________– Farm policy emphasizes ___________ and farm

commodities– Farmers are ____________ price levels for grains, cotton,

sugar, peanuts, dairy products, soybeans, etc.• Subsidies cost taxpayers____ billion in 2009– Crop ___________ and loans added $10 billion more– Subsidies occurred in spite of __________ income

Subsidies hurt the environment• They encourage excessive use of pesticides and

_______________• They reduce crop _____________ by locking

farmers into annual crop support subsidies• They encourage _______________ drawdown– For irrigation

• Subsidies __________ objectives of soil conservation

Goals of sustainable agriculture• Maintain productive topsoil• Keep food safe and wholesome• Reduce chemical fertilizers and pesticides• Keep farms economically viable• Sustainable options mimic past practices– Contouring, crop rotation, terracing, little or no chemicals

• The U.S. Sustainable Agriculture Research and Education program (SARE) (1988)– Provides $5–12 million/year for building and

disseminating knowledge about sustainable agriculture

Farm legislation• Federal Agricultural Improvement and Reform Act (FAIR)

(1996) _______ subsidies and controls– Farmers had greater ________ over what to plant

• Declining prices prompted farm ___ packages, which maintained subsidies and controls

• 2002 Farm Security and Rural Investment Act subsidized farm products and kept price supports and farm income

• The Food, Conservation and Energy Act of 2008 kept _____ subsidies and encouraged farmers to _______ grasslands– But it does have programs to _________ soil and wetlands

Conservation programs

• The Conservation Reserve Program (CRP; 1985)– Farmers are paid $125/hectare ($50/acre) per year – Highly erodible land is put into forest or grass– In 2008, 14 million hectares (34.7 million acres) were

enrolled, saving 454 million tons of topsoil from erosion/year

– The 2009 acreage was reduced to 32 million acres• Conservation activities now receive $5

billion/year– Wildlife Habitat Incentives Program (WHIP)– Environmental Quality Incentives Program (EQIP)

Other farmland conservation programs• The 2002 Conservation Security Program (CSP) – Encourages stewardship of farms, forests, watersheds– Renamed the Conservation Stewardship Program in the

2008 farm bill– $1 billion to enroll 12 million acres of farmland

• Farmers and ranchers should have incentives to protect soil– Productivity would increase

• The most significant obstacle to soil conservation– A lack of knowledge about what conservation can do– Particularly in developing countries

Solutions to overgrazing• Better management could ________ rangelands– Benefiting wildlife and ________ production

• Conservation Stewardship Program (NRCS)– Provides ________ and support to land-owning ranchers

to burn woody plants, reseed land, rotate cattle• The government could buy up some of the 26,000

permits– ___________ rangelands– Generously _______ ranchers for their permits– Use the land for wildlife, recreation, watershed

_____________

Deforestation• Porous, _________-rich forest soil efficiently holds

and recycles nutrients– Also absorbs and ________ water

• Converting a forested hillside to grassland doubles the amount of ________ and increases nutrient leaching

• When _________ are cut and soils are left exposed– Topsoil becomes saturated with water and _______ off

the slope– ___________ continues to erode

Forests are cut at alarming rates• 13 million hectares (32 million acres) are cut per year– Mostly in ____________ countries

• Cutting ___________ rain forests causes acute problems– Heavy rains have ___________ soils of minerals– Parent material is already maximally weathered– So tropical soils (__________) lack nutrients

• Clearing rain forests washes away the thin layer of _____________– Leaving only the nutrient-poor subsoil– Very _________ for agriculture

The other end of the erosion problem• Water that does not infiltrate enters streams and

____________– Causing __________________

• Sediment: _________soil carried into streams and rivers– _______ channels, intensifies floods, fills reservoirs– _______ fish and coral reefs– Damages streams, rivers, bays, ___________

• Excess sediments and nutrients from erosion are the __________ pollution problem in many areas

• Groundwater is _____________– Rainfall runs off and does not refill soil or ground water

Irrigation• Irrigation: supplying water to croplands _________– Dramatically increases ______________– Is a ___________ contributor to land degradation

• Flood irrigation: river water flows into canals to ______________ fields

• Center-pivot irrigation: water is pumped from a well into a giant pivoting _______________

• The U.S. Bureau of Reclamation is involved with supplying irrigation water to the western ________– Irrigating 4 million hectares (10 million acres)

• Worldwide irrigation is huge and is still _________