Environmental Sciences: Towards a Sustainable Future Chapter 8

1. Environmental Sciences: Towards a Sustainable Future Chapter 8 Soil and the Soil Ecosystem

2. Chapter Introduction

3. Why a Study of Soil Is Important • 90% of the world’s food comes from land-based agriculture. • Maintenance of soil is the cornerstone of sustainable civilizations. • Remember Easter Island. • Simply stated, it is the “foundation” of terrestrial life.

4. Golden Rules of Sustainable Agriculture • Cover the soil • Minimal or zero tillage • Mulch for nutrients • Maximize biomass production • Maximize biodiversity

5. Global Trend: Where Did All the Farms Go? • Poor farming practices = loss of soils and farmland. • Erosion • Salinization • US: loss to development because it is easy to develop on farm land and farmers can make huge profits. • Development in United States = loss of 600 thousand acres of farmland per year from 1992-2001.

6. Lesson 8.1 Soil and Plants

7. Soil vs. Dirt • A rich soil is much more than dirt; • Various detritus feeders/decomposers • Nutrients • Environment that is favorable to growth of roots.

8. Soil Texture • Sand • Silt • Clay Large 2.0-0.02mm Small 0.02-0.002mm Smaller finer than 0.002mm

9. Soil Texture • Soil texture refers to the percentage of each type of particle found in the soil. • Loam soil is approximately 40% sand, 40% silt, and 20% clay. (a common proportion found in soil). • Determine texture by placing a small amount into water and shaking it…it will separate into its layers allowing an estimation of the percentages. Soil scientists use a triangle that shows the relative proportions. FIGURE 8.3 page 198.

10. Topsoil Formation Soil production involves a dynamic interaction among mineral particles, detritus, and detritus feeders.

11. Soil Texture Triangle • Larger particles have larger spaces. a. Good water infiltration, aeration, workability • Smaller particles have more surface area. a. Good water and nutrient holding capacity

12. Soil Texture and Properties

13. Soil Texture

14. Soil Profile

15. Soil Classes

16. 4 of 12 Soil “Orders "Important to agriculture, animal husbandry, and forestry: • Mollisols: fertile soils with deep A horizon; best agriculture soils • Oxisols: iron and aluminum oxides in B horizon; little O horizon; Poor agriculture soils

17. Soil “orders” • Alfisols: well-developed O, A, E, and B horizons; suitable for agriculture if supplemented with organic materials. • Aridisols: little vertical structure; thin and unsuitable for sustainable agriculture.

18. For best growth, plants need: Optimal amounts of mineral nutrients Water Air (oxygen) pH and salinity are also critically important.

19. Nutrients that support growth: Supplied mostly by recycling of detritus. Leaching: Nutrients washed away as water moves through soil  leads to eutrophication.

20. Plant-soil-water Relationships

21. Productive Soil • Good supply of nutrients and nutrient-holding capacity • Infiltration, good water-holding capacity, resists evaporative water loss • Porous structure for aeration • Near-neutral pH • Low salt content • Irrigation may increase soil salinization.

22. Soil: IT’S ALIVE!

23. Lesson 8.2 Soil Degradation

24. GLASOD Soil degradation map prepared between 1987 and 1990. Data came from questionnaires sent out to soil experts around the world. Problem: very little of the data had actually been validated. The UNCCD launched a new project (LADA) to provide more accurate information.

25. Humus: To Be or Not to Be • Humus: • Partly decomposed organic matter • High capacity for holding water and nutrients • Typically found in O horizon

26. Erosion Wind or water Vegetative or litter mat helps to reduce Grass particularly helpful

27. Water Erosion: Splash, Sheet and Gully Erosion • Splash-impact of rain breaks apart clumps of top soil. • Sheet- decreased infiltration results in runoff which carries away particles from the surface. • Gully- as runoff continues, gullies form. • All of this leads to desert pavement.

28. Desert Pavement

29. Desertification • The formation and expansion of degraded areas of top soil and vegetation cover in arid, semiarid, and seasonally dry areas…not the advancing of deserts. • Forms drylands • 41% of Earth’s surface • Defined by precipitation NOT temperature.

30. Causes of Soil Degradation

31. Overgrazing • 65% of dryland areas are rangelands. • As grass production fails to keep up with consumption, the land becomes barren. • Tragedy of the commons-Overgrazing occurs because the rangelands are public lands not owned by the people who own the animals. Herders who withdraw lose income. (chapter 11)

32. Deforestation • Forest ecosystems are extremely efficient systems both for holding and recycling nutrients and for absorbing and holding water, because they maintain and protect a very porous, humus-rich topsoil.

33. Flooding • Water that can’t infiltrate, runs over the surface into streams and rivers, overflowing them and causing floods. Eroding topsoil, called sediments, clog channels and perpetuate the problem.

34. Over Cultivation • Traditionally, people plowed to control weeds. • Plowing loosens topsoils and causes erosion via wind and rain.

35. No-Till • Throughout the US, no-till is now routinely practiced. • Field sprayed with herbicide to kill weeds. • Planting apparatus used that cuts a furrow through the weed detritus, drops a seed and covers it all in one sweep. At harvest, the process is repeated so that waste from the previous crop becomes detritus and mulch cover for the next. Maintains a good topsoil. • Soil never left exposed to wind and water. • Variation: Low-till farming. One pass made over the field which will dig, plant, fertilize, and re-cover all in one step.

36. Correcting the erosion problem: No-till Low-till Contour strip cropping Shelterbelts

37. NRCS U.S. National Resource Conservation Service. Established in response to the Dust Bowl tragedy of the 1930’s Provides information to farmers regarding soil or water conservation practices.

38. Soil Degradation

39. Irrigation and Salinization • As crops are irrigated, even the freshest water (diverted from river through channels) has dissolved salts that remain behind and accumulate when the water evaporates.

40. Lesson 8.3 Conserving the Soil

41. Practicing Soil Conservation • Must be practiced on two levels: • Most important level: Individual land owner. Those working on the land are best situated to put into practice the conservation strategies that enhance the soil. • Public Policy: Soil policy CAN lead to soil disasters on an epic level.

42. Public Policy on Soil • Originally farm policy in the US was focused on increasing production. • More recently farm policy has emphasized maintaining farm income and support of farm commodities…subsidies. • Bad for the economy, bad for the environment.

43. Subsidies • Economically: US tax payers support agriculture to the tune of $74 bill. per year. Artificially maintained prices for food add another $25 bill. per year. • Environmentally: encourage excessive use of pesticides and fertilizers. Reduce crop rotation. Promote the continual draw down of ground water through irrigation.

44. Sustainable Agriculture • Goals: • Maintain productive topsoil. • Keep food safe and wholesome. • Reduce the use of chemical fertilizers and pesticides. • Keep farms economically viable.

45. Prevention of Soil Erosion • Change in attitude on national and local level • Federal programs encouraging sustainable land use • Focus of university agriculture programs

46. Soil Policies and Organizations • SARE: sustainable agriculture research and education • CRP: conservation reserve program • FAIR: federal agricultural improvement and reform act • WRP: wetland reserve program • WHIP: wildlife habitat incentives program • EQIP: environmental quality incentives program