1. Soil

2. Chemistry Review Cation: atom that forms a positive charge (example: Ca +2 ) anion: atom that forms a negative charge (example: S -2 )

3. pH Scale

8. Soil (non organic) Clay Silt Sand

10. Particle Size NameParticle diameter Sand0.05-2.0 mm Silt0.002- 0.05 mm clayLess than 0.002

11. Soil (organic) a) bacteria—base of the soil food web b) humus—decomposed organic material; dark and rich

12. composting producing humus in controlled conditions

14. What particles make up the BEST soil Clay, Silt, or Sand?

15. Water Holding Capacity Should retain water for plant growth During heavy rains, if water is not absorbed water can pool and take a long time to drain or run off resulting in flooding Most important factor: Spaces of air between the soil particles

17. Infiltration Rate Gravitational flow through soil Soils with high infiltration rate are easily leached (removing nutrients)

19. Capillary Action Strong attraction between water molecules and soil causes water to be drawn upward from the water table. Capillary action increases when soil is packed close enough to provide a continuous film of surface Soils with high rate of capillary action lose water more quickly through evaporation than soil where capillary action is slower.

21. Ion Exchange Capacity Plants need ions to use for nutrients. Soil has +/- sites where ions can bind The higher the capacity to exchange ions, the more nitrate, phosphate, and potassium ions the soil can hold, and the less likely water will wash them out Soil has sites that are either positively or negatively charged. These sites can bind with ions. If the soil can’t hold onto ions, the plants will not be able to absorb nutrients

23. Free Ions Macronutrients that plants get from soil are nitrogen N -3, phosphorus P -3, potassium K +1, calcium Ca +2, magnesium Mg +2, and sulfur S -2.

24. Soil pH soil pH close to neutral is optimal for most plants and animals

25. Soil pH Mineral cations help keep soil pH higher. When these cations are depleted, the soil pH decreases. What causes nutrient depletion in soil? 1.Plant material being removed 2.Water drains too quickly from soil it can strip soil of nutrients

26. Why is soil pH important Phosphorus soluble between 6.8 and 9 Nitrogen fixed bacteria function at specific pH If pH gets too low, aluminum becomes soluble and aluminum is toxic to plants

27. Soil Permeability If water passes too quickly through soil, the plants can not absorb the water or the nutrients dissolved in the water.

28. How is soil degraded? 1. overcultivation—frequent plowing a) crop rotation—alternating the type of crops grown b) no-till agriculture—weed control, planting, and covering up all at once (low-till farming— decrease the amount of tilling) c) contour-strip cropping—cultivation along sloping ground d) shelter belts—“belts” of trees planted around farmland to reduce wind erosion

29. Overcultivation

30. Crop Rotation

31. No-Til agriculture

32. Contour Strip

33. Shelter Belt Farming

34. 2. Frequent Planting a) problems with fertilizers inorganic chemical fertilizer does not replenish organic material mineral content remains high but soil degrades anyway

36. 3. overgrazing—animals stripping vegetation at a rate too fast for natural growth patterns to counteract it

38. 4. deforestation—depletion of forest land a) causes increased leaching and erosion b) worst-case scenario—layers above the subsoil are gone c) the other end of the erosion problem: Where do the particles go? displaced sediments can wash into rivers and streams

40. 5. Irrigation and Salinization a) irrigation—controlled introduction of water to an area b) salinization—salts accumulating in and on the soil, hindering plant growth

42. From the Environmental Literacy Council: Salt buildup is an existing or potential hazard on almost all of the 42 million acres of irrigated farmland in the United States. Much of the world‘s unused land is in arid and semiarid regions where irrigation will be necessary. Water contains a small amount of salt and over time this salt accumulates in the soil. A small amount of salt in the soil will not affect the germination and growth of crops. However, as salt concentrations increase, negative impacts occur. Eventually salt concentrations will affect the germination of seeds. Excessive salinity is presently costing the U.S. billions of dollars in lost food crops. ‖

45. Wind Erosion

46. Water Erosion

49. Irrigation

50. 2/3 of fresh water is used for irrigation Excessive irrigation = waterlogged plants

51. Farming strips nutrients in soil Farmers add fertilizers to soil to put back nutrients Nitrogen, potassium, phosphorus

52. Fertilizer Runoff