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2

Soil Resources and Sustainable Agriculture

• Ways We Use and Abuse Soil– Erosion

• Other side effects of Agriculture• Toward Sustainable Agriculture

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Erosion

• NATURAL PROCESS! Part of Rock Cycle

• What are the mechanisms for erosion?– Water– Wind– Chemical– Heavy machinery and trampling

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Fig. 11.14Percent ofAgriculturalLands withHuman-causedSoil erosion

Percent ofWorld land areaAffected byErosion types

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CS Fig 9.17

Is it a coincidence that areas of remaining Frontier Forests and areas of stable soils overlap?

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Human History of Dirt

• Agriculture started about 10,000 years ago– Evidence from increased sedimentation and

pollen from crops• Erosion increased dramatically after plow

invented ~2,000 years ago• Romans recognized problem of soil erosion and

loss of fertility– Developed soil conservation methods and soil

enrichment methods still used today

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Soil Erosion: the downfall of civilizations!

• When the soil erodes faster than it is replenished, what will happen to the soil?– It will disappear

• What happens when nutrients are used faster than they are replenished?– The soil will become sterile

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Roman Empire

• Roman Empire expanded to get new land (and slave labor) to feed Empire– Eventually over-extended themselves because soil

degradation caused them to expand so far– Land has still not recovered 2000 years later!

• George Marsh (ambassador to Italy appointed by President Lincoln) observed:– “There are parts of Asia Minor, of Northern Africa, of

Greece, and even of Alpine Europe where the operation of causes set in action by man has brought the face of the earth to a desolation almost as complete as that of the moon.”

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Mayan Civilization

• Started ~2000 BC. Large cities by 350 BC – 250 AD (~1 million people). 3-6 million people by 600-900 AD. Less than 0.5 million people 200 years later. What happened– Evidence in geologic record

• Huge surge in sediments piling up in lakes right as civilization peaked

– Practiced slash and burn agriculture• Works well for small population• Why doesn’t it work well for large populations?

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Why don’t civilizations see this coming and do something about it?!

• Lack of understanding of geologic rates– People don’t always notice soil leaving – average rate

~1 inch per hundred years (in tropical areas can reach 1 inch per decade)

• Does this sound like a lot?– Global average for soil production is 1 inch in 240 to

820 years (Deciduous forests of Maryland – 1 inch in 4,000 years)

• Even when Romans understood problem of soil erosion, couldn’t help themselves– There’s always a new place to expand into– Slaves in charge of farming didn’t have vested interest

in taking care of soil

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Examples• Land disappears and people don’t notice:

– Iceland: 1100 years of human settlement• Started out as forested island – 96% gone• 60% of vegetative cover gone• Most locals don’t even know their island was largely forested• Once soil gone, bare rock! Vegetation won’t grow back any time

soon

• Short term gains outweigh long term losses– Cash crops of newly settled America – tobacco and cotton

• Farmers exhausted the soil’s fertility and left highly rutted land and moved on

– Modern agriculture – requires expensive equipment, fertilizer, pesticides, etc.

• Farmers must make sure to make enough money to cover their costs

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Where do we stand?

• Until the 1980’s, new land brought under cultivation compensated for soil loss. Since the 1980’s, land under cultivation has been declining– Peak Soil!?

• We use 1/10th of the Earth’s land surface to grow crops and 1/4th for grazing. There is little suitable land left for expanding either.

• Where is the main place left to expand?– Is this a good idea?

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Easter Island?

• Worldwide, 38% of cropland moderately to severely degraded (UN)

• Worldwide, erosion losses same as removing 1% of cropland each year!

• Population is rising– With population rising and soil declining, does

that provide and incentive to think long term or short term?

• Worldwide ~70 inches of topsoil left on average– How long will this last?

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What can we do?• Practice no-till agriculture

– Use disk to mix organic matter into soil surface– Leave crop residue on ground– Plant seeds with chisel plow (punches seeds past

residue)– 23% of US agriculture and growing!

• Practice polyculture– Plant complimentary crops that cover the ground surface

for more of the year– Plant crops that enrich the soil (symbiotic with Nitrogen

fixing bacteria) like legumes, alfalfa• Use composted manure (animals important!!)

– Only way to actually build up the soil!

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FOOD SUPPLIES

• World food supplies have more than kept up with human population growth over the past two centuries.– 1950 - 2.5 billion people - average daily diet

was less than 2,000 calories/person.– 2001- 6.0 billion people - world food supply

can provide more than 2,500 calories/person.

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The Green Revolution

• The result of development of High Responders through agricultural research

• New plants allow high yield, yet require optimal conditions

• Made it possible for world food production to keep up with world population

CS Fig 9.25

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The Green Revolution

• Started only 50 years ago• Dwarf wheat one of earliest developments (earned

Norman Borlaug the Nobel Prize)

CS Fig 9.24

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Farmers get the “Big Squeeze”

• New varieties require optimal conditions– Farmers must be able to afford expensive

seeds, fertilizers, irrigation methods, etc.• If farmers can’t afford these things, the regular

varieties won’t produce enough yield to keep them in business

• Big business farming wins long-term

1919

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Pesticides

• Carcinogens affect humans and wildlife• Insects become resistant, requiring more

pesticides!

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Modern vs. Sustainable Farming

• Modern methods fight against natural processes– Soil loss requires increasing amounts of fertilizer,

Pesticide use escalates, creates vicious cycle• Sustainable methods work with natural processes

Diversification is key• Soil erosion reduced, nutrients replenished naturally, need

for pesticides reduced (natural microbes much higher)

– Natural fertilizer (manure, crop rotations)• Can Sustainable methods feed the world?

– YES! – Why? They have to.

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Analysis

• Sustainable/organic farming advantages– Use 1/3 to ½ of fertilizer, energy used in

conventional methods– Use virtually no pesticides– Soil condition improves instead of degrades– Same to 20% lower harvests, but with lower

costs, profits are same or better

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Farm Subsidies

• Complicated economic issue!– Subsidies at home, tariffs at home and abroad

• Eyebrow raising fact:– 1/10th of producers get 2/3 of the subsidies– Lobby hard to keep subsidies

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Genetic Engineering

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The Role of Genetic Engineering?

• The next wave of the Green Revolution?

• The Good: less pesticide use required, poor soils could be productive

• The Bad: more herbicide use possible, “contamination” of wild species, lowered pest resistance

CS Fig 11.22

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It’s already begun

• Current GMO’s– 82% of all soybeans– 71% of cotton– 25% of corn

• 60% of processed food in America has GMO ingredients – YOU’RE EATING THEM ALREADY!!

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GMO’s: The big scam?

• The National Academy of Sciences’ Agricultural Board found that GMO soybeans give smaller harvests than natural seeds in over 8,000 trials!

• The US Department of Agriculture found that there was no reduction in pesticide use, even though a decrease in pesticide use was advertised as being a benefit

• GMO and high-yield seeds are proprietary. The companies can sue you if some of the plant seeds itself because you didn’t pay for that seed. A farmer in Canada fought and won, but many don’t fight.

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Peak Soil vs Peak Oil

• How can you tell when a non-renewable resource has peaked and will no longer be available in the amounts it was in the past?– Relationship between price and long term

supply not quite that simple, but good indicator• What is driving up price of food?

– Increased demand?– Decreased supply? Why?

• How is soil different from oil?

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The End.

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