Soil, Food and Agriculture Chapters 14 a nd 23

1. Soil, Food and AgricultureChapters 14 and 23

2. Soil: the foundation for agriculture Soil is a thin covering over most land that is a complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, air, and billions of living organisms, most of them microscopic decomposers

3. Soil is important because: • It provides most of the nutrients needed for plant growth, and subsequently consumer growth. • It is the primary filter that cleanses water as it passes through. • It is a major component of the earth’s water recycling and water storage processes.

4. Components of soil 25% air (mostly N and O) 25% water 45% mineral 5% organic matter Amounts of air and water vary

5. Soil is a renewable resource Formation of soil depends on 5 factors: 1. climate 3. biologic activity 5. time 2. terrain 4. geology It takes 15 to 100s of years to form one cm of soil! * ** *Parent material = the base geologic material of soil **Bedrock = the continuous mass of solid rock comprising the Earth’s crust

6. Weathering produces soil • Weathering = the physical, chemical, or biological processes that break down rocks to form soil • Physical (mechanical) • wind and rain • no chemical changes in the parent material • Chemical • substances chemically interact with parent material • Biological • organisms break down parent material

7. Soil Horizons: Layers of mature soil O horizon – organic material, leaf litter, many organisms live here A horizon – topsoil layer, zone of accumulation of organic matter and nutrients These top 2 horizons contain: - the roots of most plants - billions of living things (bacteria, fungi, earthworms, insects, etc.)

9. Soil Horizons: Layers of mature soil B horizon – subsoil, accumulates iron, clay, aluminum and organic compounds that leach down from above (leaching: process in which water seeps down through open spaces or pores in soil, dissolving minerals and organic matter and carrying them to lower layers)

10. Soil Horizons: Layers of mature soil C horizon – parent material, contains large lumps or shelves of rock R horizon (under C horizon)- bedrock

11. Soil Particles Three types, based on size: • Sand: 2.0-0.05 mm • Silt: 0.05-0.002mm • Clay: less than 0.002mm Relative amounts determine soil texture

12. Soil Textural Classification

13. Soil Permeability Definition: the rate at which water and air move from upper to lower soil layers The more spaces there are between soil particles, the more permeable it is Plants need good drainage, but not too much

14. Plants are like Goldilocks Sandy soil: This soil is too permeable – water runs right through Clay soil: This soil is too impermeable – water can’t get through Loam: This soil is just right! (mixture of sand and clay) Which is which? Sand on left Loam in middle Clay on right

15. Other soil characteristics that are important to plants • Nutrient content – nitrogen (N), phosphorus (P) and potassium (K) • pH – if soil is too acidic or basic, plants can’t grow

16. Agriculture and Population Growth The earth has a carrying capacity for the human population – we don’t know what it is. We do not have unlimited land and resources to produce food for people.

17. How do we supply 7 billion people with enough food? • Agriculture = practice of raising crops and livestock for human use and consumption • Cropland = land used to raise plants for human use • Rangeland or pasture = land used for grazing livestock Land devoted to agriculture covers 38% of Earth’s land surface

18. Agriculture arose 10,000 years ago • Agriculture was invented independently by different cultures • The earliest plant and animal domestication is from the “Fertile Crescent” of the Middle East • Wheat, barley, rye, peas, lentils, onions, goats, sheep

19. Traditional agriculture • Traditional agriculture = biologically powered agriculture, using human and animal muscle power • Subsistence agriculture = families produce only enough food for themselves • Uses animals, irrigation and fertilizer, but not fossil fuels

20. Industrialized agriculture is a recent phenomenon • Industrialized agriculture = using large-scale mechanization and fossil fuels to boost yields • Yield = amount of food that can be produced in a certain area • Also uses pesticides, irrigation and fertilizers • Monocultures = uniform planting of a single crop • Why might monocultures be a bad idea?

21. Monocultures increase output, but at a cost • Monoculture = a large expanse of a single crop • More efficient, increases output • Devastates biodiversity • Susceptible to disease and pests • Narrows human diet: 90% of our food comes from 15 crop species and 8 livestock species Armyworms easily defoliate monocultures

22. Dramatically increased per-acre yields Spread to the developing world in the 1940s with wheat, rice, corn Depended on large amounts of Synthetic fertilizers Chemical pesticides Irrigation Heavy equipment The Green Revolution

23. Humans and Nutrition Food provides 1. Energy (Calorie = amount of heat required to raise the temperature of one kilogram of water by one degree at one atmosphere pressure) 2. Materials to build body (carbon, proteins, minerals, lipids, etc.)

24. Nutrients Humans need a variety of foods to supply their nutritional needs Maj0r categories of nutrients: • Carbohydrates • Proteins • Fats • Vitamins • Minerals The Food Pyramid is a guide for what we should eat daily.

25. Nutrient deficiencies Malnutrition – a condition when a person does not consume enough calories or nutrients to supply the body’s needs Marasmus (“wasting away”)– not enough calories and protein Kwashiorkor (“displaced child”) – severe protein deficiency, bloated belly, can cause mental retardation

26. Overnutrition – too many calories, results in health problems including diabetes, heart disease, stroke

27. We face food issues as our population grows:

28. 1. Lack of enough arable land Graph showing per capita arable land over time:

29. 2. Soil degradation soil erosion – the dislodging and movement of soil by wind or water, occurs when vegetation is absent Erosion increases through: excessive tilling, overgrazing, and clearing forests Can result in desertification - most prone areas are arid and semiarid lands

30. The Dust Bowl • In the late 19th and early 20th centuries, settlers arrived in Oklahoma, Texas, Kansas, New Mexico and Colorado • Grew wheat, grazed cattle • Removed vegetation • A drought in the 1930s made conditions worse • Thousands of farmers left their land and had to rely on governmental help

31. We lose 5-7 million ha (12-17 million acres) of productive cropland annually

32. 3. Uneven food distribution around the world Developing countries: usually faster population growth, more poverty, less infrastructure to grow and distribute food

33. 4. Problems with irrigation • Irrigation = Artificially providing water to support agriculture • Unproductive regions become farmland • Only about 3% of the world’s land is suitable for farming without adding water • Waterlogging = over-irrigated soils • Water suffocates roots • Salinization = the buildup of salts in surface soil layers • Depletion of ground and surface waters

34. 5. Loss of biodiversity When we convert natural habitats to farms, we reduce natural habitat We also plant monocultures and use few species for crops

35. 6. Negative effects of overgrazing • Soil compaction • Non-native invasive species invade • Less palatable to livestock • Out compete native vegetation Ungrazed plot Grazed plot

36. 7. Pollution from: Agriculture - pesticides, herbicides, fertilizers, Livestock (on feedlots) – animal waste, excess methane is a greenhouse gas

37. Overapplication of Fertilizer • Inorganic fertilizer use has skyrocketed • Overapplying fertilizer can ruin the soil and severely pollute several areas • Runoff causes eutrophication in nearby water systems • Nitrates leach through soil and contaminate groundwater • Nitrates can also volatilize (evaporate) into the air

38. Eutrophication of the Gulf of Mexico – The Dead Zone • Seasonal – starts in spring with the beginning of the growing season in the central U.S. and fades in the winter

40. 8. Resistance to pesticides • Some individuals are genetically immune to a pesticide • They survive and pass these genes to their offspring • Pesticides stop being effective • Evolutionary arms race: chemists increase chemical toxicity to compete with resistant pests

41. Solutions to our agriculture issues:

42. 1. Sustainable Agriculture • Industrial agriculture may seem necessary, but less-intensive agricultural methods may be better in the long run • Sustainable agriculture = does not deplete soil, pollute water, or decrease genetic diversity

43. 2. Protecting soil: crop rotation and contour farming • Crop Rotation = alternating the crops grown field from one season or year to the next, • Cover crops protect soil when main crops aren’t planted • Wheat or corn and soybeans • Contour Farming = plowing furrows sideways across a hillside, perpendicular to its slope, to prevent rills and gullies

44. Protecting soil: terracing and intercropping • Terracing = level platforms are cut into steep hillsides, sometimes with raised edges • A “staircase” to contain water • Intercropping = planting different types of crops in alternating bands or other spatially mixed arrangements • Increases ground cover

45. Pros and cons of no-till farming • Almost half of U.S. farmland uses no-till farming • Benefits: reduced soil erosion, greater crop yields, enhanced soils • Negatives: increased use of herbicides and fertilizers

46. 3. Biological control • Biological control (Biocontrol) = uses a pest’s natural predators to control the pest • Reduces pest populations without chemicals • Cactus moths control prickly pear • Bacillus thuringiensis (Bt) = soil bacteria that kills many pests

47. 4. Salinization prevention • It is easier and cheaper to prevent salinization than fix it • Do not plant water-guzzling crops in sensitive areas • Irrigate with low-salt water • Irrigate efficiently, supplying only water that the crop requires • Drip irrigation targets water directly to plants

48. 5. Integrated Pest Management (IPM) • IPM uses multiple techniques to suppress pests • Biocontrol • Chemicals, when necessary • Population monitoring • Habitat alteration • Crop rotation and transgenic crops • Alternative tillage methods • Mechanical pest removal Within 4 years of using IPM in Indonesia, rice yields rose 13%, and $179 million saved by phasing out subsidies

49. 6. Genetically Modified Organisms (GMOs) • Genetic engineering = laboratory manipulation of genetic material • Genetically modified organisms = organisms that have been genetically engineered by … • Recombinant DNA = DNA created from multiple organisms

50. Genetic engineering has both benefits and risks • Benefits of genetic engineering: • Increased nutritional content • Increased agricultural efficiency • Rapid growth • Disease and pest resistance • Negatives of genetic engineering: • Risks are not yet defined or well understood • Protests from environmental activists, small farmers, and consumer advocates