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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 12

3. Erosion NATURAL PROCESS! Part of Rock Cycle
What are the mechanisms for erosion?
Water
Wind
Chemical
Heavy machinery and trampling

4. Fig. 11.14 Percent of Agricultural Lands with Human-caused
Soil erosion
Percent of
World land area
Affected by
Erosion types

5. CS Fig 9.17
Is it a coincidence that areas of remaining Frontier Forests and areas of stable soils overlap?

6. 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

7. 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

8. 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.”

9. Mayan Civilization
Started ~2000 BC. Large cities by 350 BC – 250 AD (~1 million people). 3-6 million people by 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?

10. 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

11. 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

12. 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?

13. 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?

14. 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!

15. FOOD SUPPLIES
World food supplies have more than kept up with human population growth over the past two centuries.
billion people - average daily diet was less than 2,000 calories/person.
billion people - world food supply can provide more than 2,500 calories/person.

16. The Green Revolution CS Fig 9.25
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

17. The Green Revolution Started only 50 years ago
Dwarf wheat one of earliest developments (earned Norman Borlaug the Nobel Prize)
CS Fig 9.24

18. 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

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20. Pesticides Carcinogens affect humans and wildlife
Insects become resistant, requiring more pesticides!

21. 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.

22. 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

23. 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

24. Genetic Engineering

25. 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

26. 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!!

27. 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.

28. 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?

29. The End.
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