1. Chapter 9 Topics: The relationship between soils and agriculture
Major agricultural developments
Fundamentals of soil science
Causes/consequences of soil erosion/degradation
Soil conservation: principles, solutions, and policies

2. Soil: foundation of agriculture
38% of land surface used for agriculture
Agriculture = practice of raising crops and livestock for human use and consumption
Cropland = land used to raise plants for human use
Rangeland/pasture = land used for grazing
Soil = a complex plant-supporting system
Consists of disintegrated rock, organic matter, water, gases, nutrients, and microorganisms
It is a renewable resource that can be depleted

3. The need to feed more of us
Feeding a growing human population requires
Increasing agricultural production or
Changing our diets
Land suitable for farming is running out
Mismanaged agriculture degrades soils
Allows fertile soil to be eroded
Turns grasslands into deserts
Removes forests

4. Agriculture arose 10,000 yrs ago
Many cultures independently invented agriculture
The earliest plant and animal domestication is from the “Fertile Crescent” of the Middle East

5. Traditional agriculture
Agriculture allowed people to settle in one place
Populations increased
Leading to more intensive agriculture
Traditional agriculture = biologically powered
Uses human and animal muscle power
Hand tools, simple machines
Subsistence agriculture = families produce only enough food for themselves
Polyculture = different crops are planted in one field

6. Industrialized agriculture
Industrialized agriculture = uses large-scale mechanization and fossil fuels to boost yields
Also uses pesticides, irrigation, and fertilizers
Monoculture = uniform planting of a single crop
Green revolution = new technology, crop varieties, and farming practices were introduced to developing countries
Increased yields and decreased starvation
Created new problems and worsened old ones

7. Soil as a system
Soil consists of mineral and organic matter, air, and water
Soil is a habitat for earthworms, insects, mammals, reptiles, and amphibians
Soil is an ecosystem

8. Soil formation is a slow process
Parent material = the initial rock or sediment
Weathering = processes that form soil
Physical (mechanical) = no chemical changes in the parent material (changes to size and shape)
Chemical = parent material is chemically changed
Organisms are important agents of both physical and chemical weathering
Humus = spongy, fertile material formed by partial decomposition of organic matter

9. Processes/factors of soil formation
The processes:
Additions, accumulations
Transformations, removals
The factors:
Climate: soils form faster in warm, wet climates
Organisms: plants/decomposers add organic matter
Topography: affect exposure to sun, water movement
Parent material: influences properties of resulting soil
Time: soil can take decades to millennia to form

10. A soil profile consists of horizons
Horizon = a soil layer
Soil profile = the cross- section of soil as a whole
Topsoil = inorganic and organic material most nutritive for plants
Leaching = dissolved particles move down through horizons

11. Characterizing soils
Soil color = indicates its composition and fertility
Black or dark brown = rich in organic matter
Pale gray or white = indicates leaching
Soil texture = determined by the size of particles
From smallest to largest: clay, silt, sand
Loam = soil with an even mixture of the three
Affects how easily air and water travel through the soil
Influences how easy soil is to cultivate

12. Characterizing soils Soil structure = a measure of soil’s “clumpiness”
A medium amount of clumpiness is best for plants
Repeated tilling compacts soil, decreasing its water- absorbing capabilities
Soil pH = affects the ability to support plant growth
Soils that are too acidic or basic can kill plants
pH influences the availability of nutrients for plant

13. Characterizing soils Cation exchange = allows plants to gain nutrients
Negatively charged soils hold cations (positively charged ions) of calcium, magnesium, and potassium
Roots exchange hydrogen to soil for these nutrients
Cation exchange capacity = ability to hold cations
Cations that don’t leach are more available to plants
A useful measure of soil fertility
Greatest in fine or organic soils

14. Regional differences
In rainforests, the nutrients are in plants, not the soil
Rain leaches minerals and nutrients, reducing their accessibility
Rapid decomposition of leaf litter results in a thin topsoil layer with little humus

15. Regional differences
In temperate prairies, the nutrients can accumulate in the soil
Lower rainfall leaches fewer nutrients
Long root systems extend organic matter deep into the soil

16. Land degradation
Human activities reduce and limit productivity by degrading soils in many areas
Land degradation = a general deterioration of land, decreasing its productivity and biodiversity
Erosion is the leading cause of land degradation
Other effects include loss of organic matter, nutrient depletion, water issues (scarcity, salinization, water- logging), changes to structure, chemical pollution

17. Erosion The removal of material by water, wind, glaciers
Occurs more easily on steeper slopes
The uppermost material, the topsoil, is removed first
Often occurs faster than soil is formed
Land is made more vulnerable to erosion through
Over-cultivating fields (over-use or excessive tilling)
Overgrazing rangelands
Clearing forests on steep slopes or with large clear-cuts

18. Erosion can be prevented
Erosion can be hard to detect and measure
Five tons/acre is lost per ton of grain
This amounts to a layer only as thick as a penny
Physical barriers to capture soil can prevent erosion
Plants can reduce soil loss by slowing wind/water
Roots hold soil in place
No-till agriculture leaves plant residue on fields
Cover crops protect soil between crop plantings

19. Desertification
Desertification = a loss of more than 10% productivity due to
Erosion, soil compaction
Deforestation, overgrazing
Drought, salinization, water depletion
Climate change
Areas most prone are arid and semiarid lands

20. Impacts of desertification
Affects one-third of the planet’s land area
In over 100 countries
Endangering food supplies of 1 billion people
It costs tens of billions of dollars each year
China loses over $6.5 billion/year from overgrazing
80% of land in Kenya is vulnerable
Desertification can be a positive feedback cycle
Degradation forces farmers onto poorer land
Farmers reduce fallow periods, so land loses nutrients

21. The Dust Bowl
Late 1800 – early 1900, growing of wheat, grazing cattle removed vegetation
Dust Bowl = 1930s drought + erosion caused “black blizzards” of sand and silt
Thousands of farmers left their land and were forced to rely on governmental help

22. Soil Conservation Service (SCS)
Started in 1935, the Service works with farmers to:
Assess the land’s resources, problems, opportunities
Develop conservation plans for farms
Work with landowners to implement conservation plans
Conservation districts = organized by states, operate with federal direction and funding
SCS is now called Natural Resources Conservation Service (NRCS); added responsibility for water quality protection and pollution control

23. Techniques for protecting soil
Crop rotation = different crops from year to year
Reduces pests
Legumes fix N
Contour farming = plowing level furrows
Prevents rills/gullies
Enhances infiltration

24. Techniques for protecting soil
Terracing = level platforms cut into steep hillsides
Intercropping = planting different crops in alternating bands
Increases ground cover
Replenishes soil
Decreases pests and disease

25. Techniques for protecting soil
Shelterbelts (windbreaks) trees planted along the edges of fields slow the wind
Conservation tillage reduces amount of tilling
Leaves at least 30% of crop residues in the field
No-till farming disturbs the soil even less

26. Conservation tillage Increases organic matter and soil biota
Reduces erosion and improves soil quality
Prevents carbon from returning to the atmosphere
Reduces fossil fuel use
May increase use of herbicides and fertilizers
40% of U.S. farmland uses conservation tillage

27. Plant cover reduces erosion
Plants anchor soil
Techniques that increase plant cover
Cover crops that become green manure
Move livestock to prevent overgrazing
Cut fewer trees
Plant vegetation along riverbanks & roadsides

28. Irrigation issues - quantity
Irrigation = providing water to support agriculture
Unproductive regions become productive farmland
Waterlogging = when soils are over-irrigated, the water suffocates roots
Inefficiencies in application
Large volumes of water evaporate during spraying
Watering needs may vary within a field

29. Irrigation issues – quality
Salinization = when soils are “under-irrigated”, salts accumulate in surface soil layers
Water volume insufficient to drain out of root zone
Inhibits production of 20% of irrigated cropland, costing over $11 billion/year
Easier and cheaper to prevent than to fix
Avoid water-guzzling crops in sensitive areas
Irrigate with low-salt water

30. Fertilizers Fertilizers = substances containing essential nutrients
Inorganic fertilizers = mined or synthetically manufactured
Inorganic fertilizer use has increased significantly
Inorganic fertilizers are chemically simpler and more mobile in the environment

31. Fertilizers Organic fertilizers = remains/wastes of organisms
Manure, crops/residues
Compost = produced when decomposers break down organic matter
Organic fertilizers improve:
Soil structure
Nutrient retention
Water-retaining capacity

32. Overgrazing Overgrazing = over-use of rangeland or pasture
70% of the world’s rangeland is degraded, costing $23.3 billion/year
U.S. government subsidies include few incentives to protect rangeland

33. Impacts of overgrazing

34. Agricultural policy
Industrial agriculture puts huge demands on the land
Farming can be a year-to-year gamble, encouraging a short-term perspective
Degradation occurs slowly and can be hard to see
Subsidies encourage cultivation on fragile land
Ranchers graze cattle extremely cheaply on BLM (Bureau of Land Management) land
Agriculture can be sustainable, but there is a lot of “policy inertia” in favor of the status quo

35. Wetlands then and now
Wetlands = swamps, marshes, bogs, river floodplains
Government policy encouraged draining
Swamp Lands Acts (1849, 1950, 1860) = drained and converted wetlands to control floods and malaria
Over 50% have been drained for agriculture
Wetlands are now seen as vital ecosystems
Provide habitat, flood control, recharged water supplies
Wetlands Reserve Program = landowners are paid to protect, restore, and enhance wetlands

36. A direction for the future?
Conservation Reserve Program (1985): farmers are paid to put highly erodible land in conservation reserves
Trees and grasses are planted instead of crops
Each dollar spent saves 1 ton of topsoil
Generates income for farmers
Improves water quality
Provides habitat for native wildlife
The 2008 farm bill limited reserve lands to 32 million acres but funded 14 similar land conservation programs