Understanding the Relationship Between Soils and Agriculture

2. This lecture will help you understand: • The relationship between soils and agriculture • Major agricultural developments • The fundamentals of soil science • Causes and consequences of soil erosion and degradation • Principles of soil conservation

3. No-till agriculture in Southern Brazil (1990s)Tilling: common practice of turning the earth by plowing, harrowing in Europe, Asia, etc. But, Problems in subtropical regions with heavy rain fall • Southern Brazil: maize, wheat, soy beans. • Repeated tilling & planting has diminished the productivity of the soil top soil loss → eroded away by rain and wind → crop yields reduced • Leaving crop residues on their fields after harvesting and planting “cover crops” reduced erosion, increased yields & cut costs

4. Soil: the foundation for agriculture • Land for agriculture covers 38% of Earth’s land surface • 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 • Soil = a complex plant-supporting system consisting of disintegrated rock, organic matter, water, gases, nutrients, and microorganism. It is a renewable resource Cf. ~ 7 Billion, 38% Agriculture (2011) 40% Services 22% Manufacturing Industry

5. Population and consumption degrades soil • Feeding the world’s rising human population requires changing our diet or increasing agricultural production • Land suitable for farming is running out • We must find ways to improve the efficiency of food production • Mismanaged agriculture turns grasslands into deserts; removes forests; diminishes biodiversity; and pollutes soil, air, and water • Fertile soil is blown and washed away

6. Millions of acres of cropland are lost each year We lose 5-7 million ha (12-17 million acres) of productive cropland annually (cf. GA: 60,000sq. mi = 15 M ha = 38M acres)

7. Soil degradation has many causes • Soil degradation results from deforestation, agriculture and overgrazing • Over the past 50 years, soil degradation has reduced global grain production by 13%

8. Agriculture arose 10,000 years ago: ← Hunter/gatherer • 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 Start 10/16/008

9. From Hunter/gatherer (for 250,000 yrs) to Settler Plant Animal Species Time(BC) Origins Species Time(BC) Origins This change eventually lead to the first city state and the rise of civilization some 4,000~5,000 yrs ago • Dog: 15,000 E. Asia , Africa • Sheep,Goat: 10,000 SW Asia, Iran • Pig: 9,000 Near East • Cow: 8,000 India, Middle East • Chicken: 6,000 India, SE Asia • Horse: 4,000 Eurasian Steppes • Honeybee: 4,000 (Multiple Places) • Silkworm: 3,000 China Wheat, Peas: 9,500 Mesopotamia Rice, Millet: 7,500, Asia Squash 7,000, Mesoamerica Wheat, Legumes: 6,000, Indus Valley Sorghum, Rice: 5,000, Sahel Cotton: 4,000, Indus Val. Maize: 3,000, Mesoamerica Note: the Ages determined with Radio Carbon Dating Method: 14C → 14N + e- t1/2 = 5,730 yrs Start 10/16/008

10. Traditional agriculture • Traditional agriculture : biologically powered agriculture, using human and animal muscle power • Subsistence agriculture : families produce only enough food for themselves • Intensive agriculture : produces excess food to sell Uses animals, irrigation and fertilizer, but not fossil fuels Tool Materials: Old Stone Age New Stone Age Bronze Age Iron Age - Middle Age Modern Age (Plastics) Start 10/16/008

11. Mammal(220M), Primate (50M), Hominid(5M), Homo(2M), H. Sapience(0.25M) • Paleolithic Ages (2,500,000~ 10,000 BP): Hunting & Gathering (Last Ice Age: 110,000~10,000 BP, peak:18,000) “Where Mt. Tuba Eruption: 74,000 BP (10 yrs of winter) to Move?” • Mesolithic Ages (20,000-12,000 BP): Hunting & Gathering (Last Ice Age ends at 10,000 BP) • Neolithic Ages (12,000~4,500BP): revolutionary, “How to settle better?” Farming, Hunting & Gathering, Fishing, Animal Domestication - Pre-pottery Neolithic (9,400 -6,500BC) Early village/town: Jerico, Catal Huyuk(~7,700 BC) - Pottery Neolithic (6,500-4,500 BC) (Stonehenge) • Chalcolithic Ages (4,500 BC-): Farming, cattle, breeding, craft, trading • Bronze Age (3,500 BC -): Farming, cattle, breeding, craft, trading • Iron Age (1,200 BC -): Farming cattle, breeding, craft, trading Mediterranean & Europe(9~12C BC), India & Sri Lanka, (10C BC), Britain (8C BC), Sub-Sahara (12C BC), China(6C BC), Korea (4C BC), Japan (3C BC)

12. Industrialized agriculture is a recent phenomenon • Industrialized agriculture = using large-scale mechanization and fossil fuels to boost yields • Also uses pesticides, irrigation and fertilizers • Monocultures : very effective uniform planting of a single crop in vast are • Green revolution : the use of new technology, crop varieties and farming practices introduced to developing countries • Increased yields dramatically

13. Soil as a system • Soil consists of mineral matter, organic matter, air, and water • Dead and living microorganisms, and decaying material • Bacteria, algae, earthworms, insects, mammals, amphibians, and reptiles Since soil is composed of living and non-living matter, it is considered an ecosystem

14. Soil formation is slow and complex • Parent material: the base geologic material of soil • volcanic ash, rock, dunes • Bedrock: the continuous mass of solid rock comprising the Earth’s crust • 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 react with parent material (H2O, O2, CO2, H2CO3, etc.) • Biological : Physical disruption by plant roots, Bacterial action to help breakdown of parent material

15. Rocks Weather to produces soil Chemically broken down mostly by Carbonic acid (H2CO3) to Sand: Quartz (SiO2) plus → Clay: Kaolinite (Al2Si2O5(OH)4) • Granite: Quartz (SiO2, Inert, do not react) • Feldspar (KAlSi3O8) • Albite (NaAlSi3O8) • and Others

16. Soils are characterized in many ways • Soils are classified based on color, texture, structure, & pH • 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 Influences how easy it is to cultivate and let air and water travel through the soil

17. Twelve Classes of Soil texture Silty soils with medium-size pores, or loamy soils with mixtures of pore sizes are best for plant growth and crop agriculture The Composition: 20 % Clay 40% Silt 40% Sand *

18. A Soil Profile: the cross-section of soil as a whole consists of horizons(= each layer of soil) • Up to six major horizons may occur in a soil profile - O Horizon: litter layer on surface • Topsoil (A): inorganic and organic material most nutritive for plants (Humus) • Leaching : dissolved particles move down through E horizons to B(Subsoil, mineral accumulates) • C: weatherparental rock • R: purebed rock Cf. Lake or Sea bottom

19. Soil structure and pH • Soil structure: a measure of soil’s “clumpiness” • Large clumps can discourage plant roots • Repeated tilling compacts soil, decreasing its water-absorbing capabilities • Plowpan: a hard layer resulting from repeated plowing that resists water infiltration and root penetration • Soil pH: influences a soil’s ability to support plant growth • Soils that are too acidic or basic can kill plants

20. Cation exchange is vital for plant growth • Cation exchange: process that allows plants to gain nutrients • Negatively charged soils hold cations (positively charged ions) of calcium, magnesium, and potassium • Cation exchange capacity: a soil’s ability to hold cations, preventing them from leaching, thereby increasing their availability to plants • A useful measure of soil fertility • Greatest in fine soils (or clay, the smallest particles)

21. Processes affect soil formation • Erosion: the dislodging and movement of soil by wind or water • Occurs when vegetation is absent • Biological activity includes deposition, decomposition, and accumulation of organic matter • Humus: a dark, spongy, crumbly mass of material formed by partial decomposition

22. Various types of soil erosion Splash Sheet Rill Gully

23. Soil erodes by several methods • Plants protect soils form erosion • Removing plants accelerates erosion • Rill erosion moves the most topsoil, followed by sheet and splash forms of erosion • Water erosion occurs most easily on steep slopes • Erosion in the U.S. declined between 1982 and 2001 • Soil conservation measures Despite conservation measures, the U.S. still loses 6 tons of soil for every ton of grain harvested

25. Soil erosion is a global problem • Humans are the primary cause of erosion • It is occurring at unnaturally high rates • In Africa, erosion over the next 40 years could reduce crop yields by half • Coupled with rapid population growth, some observers describe the future of agriculture as a crisis situation

26. Desertification • Desertification: a loss of more than 10% productivity • Erosion, soil compaction, forest removal, overgrazing, salinization, climate change, depletion of water sources • Most prone areas: arid and semiarid lands

27. Desertification has high costs • Desertification affects 1/3 of the planet’s land area • In over 100 countries • Costs tens of billions of dollars each year • China loses over $6.5 billion/year alone from goat overgrazing • In Kenya, 80% of he land is vulnerable to desertification from overgrazing and deforestation

28. 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

29. Protecting soil: crop rotation and contour farming • Crop Rotation: alternating the crops grown field from one season or year to the next, • Return nutrients to soil that are depleted by one crops from repeated use • Wheat or corn and soybeans • Rotate even with animal farm cf. Hog Farm, Iowa (2010) • Contour Farming = plowing furrows sideways across a hillside, perpendicular to its slope, to prevent rills and gullies

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

31. Protecting soil: shelterbelts and reduced tillage • Shelterbelts or Windbreaks : rows of trees or other tall, perennial plants that are planted along the edges of fields to slow the wind • Reduced Tillage: furrows are cut in the soil, a seed is dropped in and the furrow is closed • No-till farming disturbs the soil even less

32. 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 • But, green manure (dead plants and fertilizer) and rotating crops minimizes the negatives

33. Plant cover reduces erosion • Eroding banks along creeks and roadsides are stabilized by planting plants to anchor soil • China has the world’s largest tree-planting program • It does slow erosion • But it does not create ecologically functional forests, because monocultures are planted

34. Irrigation: boosted productivity, but problems, too • Irrigation = Artificially providing water to support agriculture • Unproductive regions become farmland • Waterlogging = over-irrigated soils • Water suffocates roots • Salinization = the buildup of salts in surface soil layers (Ca, Mg Salts) water => very hard (SW US) • Worse in arid areas Concentration of Calcium: < 40ppm > 100ppm Soft Hard Salinization inhibits production of 20% of all irrigated cropland, costing more than $11 billion/year

35. 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 (soft) Rain water (the best, No Ca) • Irrigate efficiently, supplying only water that the crop requires • Drip irrigation targets water directly to plants

36. Fertilizers boost yields, but cause problems • Fertilizer : substances that contain essential nutrients N, P, K (BTW, where in plants & animals are these needed?) • Inorganic fertilizers: mined or synthetically manufactured mineral supplements - NH3, NH4NO3, Ca(H2PO4)2, etc • Organic fertilizers : the remains or wastes of organisms • Manure ((NH4)2CO, etc.), crop residues, fresh vegetation • Compost: produced when decomposers break down organic matter (Home garden) Applying synthetic fertilizer vs. Planting rye, a “green manure”

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 (NH4)2CO NH3, NH4NO3, (NH4)2SO4, (NH4)2HPO4, Ca(H2PO4)2, etc

38. Environmental effects of over-fertilizing Eutrophication: over-enrichment of nutrients in natural water causes excessive growth of plankton → oxygen depletion(hypoxia) End 10/16/2008 – finished Chapter

39. Overgrazing causes soil degradation • Overgrazing = too many animals eat too much of the plant cover • Impedes plant regrowth • A leading cause of soil degradation • Government subsidies provide few incentives to protect rangeland 70% of the world’s rangeland is classified as degraded

40. Forestry impacts soil Along withfarming and ranching, forestry impacts soils Clear-cutting = the removal of all trees from an area at once Leads to soil erosion, especially on steep slopes Modern methods remove fewer trees over longer periods of time Minimizes soil erosion

41. U.S. programs promote soil conservation Food Security Act of 1985: (the 1985 Farm Bill) to help farmers that adopt soil conservation plan to receive price supports and other benefits Conservation Reserve Program (1985) Farmers are paid to place highly erodible land into conservation reserves Trees and grasses are planted instead of crops Saves 771 million tons of topsoil per year (~792 m or half a mile) cubed Generates income for farmers Provides habitat for native wildlife

42. Other Acts: Food, Agriculture, Conservation, & Trade Act of 1990 (the 1990 Farm Bill) and Federal Agriculture Improvement and Reform Act of 1996 (the 1996 Farm Bill), to promote the conservation of wetlands on agricultural lands. protection of wildlife habitat and water quality.

43. International soil conservation programs Food and Agriculture Organization (FAO) : the United Nations’ main agricultural organization Farmer-Centered Agricultural Resource Management Program (FAR) → a grassroots approach (bottom-up) Helps farmers duplicate agricultural success stories Uses local communities to educate and encourage farmers to conserve soils and secure the food supply Supports innovative approaches to resource management and sustainable agriculture in around the world China, Thailand, Vietnam, Indonesia, Sri Lanka, Nepal

44. QUESTION: Review Traditional subsistence agriculture uses all of the following, except: • Animal power • Irrigation • Irrigation water • Fossil fuels

45. QUESTION: Review Physical weathering is characterized by: • The chemical interaction of water with parent material • Organisms breaking down parent material • Wind or rain breaking down parent material • The dislodging or movement of soil by wind

46. QUESTION: Review Which horizon is the most valuable for agriculture? • Topsoil (A horizon) • E horizon • B horizon • R horizon

47. QUESTION: Review Erosion increases through all of the following, except: • Excessive tilling • Overgrazing • Clearing forests • All of the above increase erosion

48. QUESTION: Review Which sustainable farming method involves planting rows of trees along field edges to slow the wind? • Terracing • Crop rotation • Shelterbelts • Contour farming

49. QUESTION: Weighing the Issues Should developed nations fund reforestation projects in developing nations to combat erosion and deforestation? • Absolutely, developing nations are facing a crisis • No, not with money, but developed nations could give advice • No, developed nations had to solve their problems, let the others solve their own problems • I don’t care, it doesn’t really affect me

50. QUESTION: Weighing the Issues Should the U.S. government provide farmers with financial incentives to use technologies such as no-till farming and crop rotation? • Absolutely, farmers may be more likely to switch to these techniques • Yes, but farmers must put any money received into the farm • No, it’s not the government’s job to interfere with farming practices • I don’t care, it doesn’t really affect me