1. SOIL FORMATION Chapter 2

5. Processes of Soil Formation

18. → →

22. Rock

28. 2KAlSi 3 O 8 + 13H 2 O → Al 2 O 3 + 6H 4 SiO 4 + 2K + + 2OH - Rock

29. → → Fe 3+

30. Rock It fizzes because CaCO 3 + 2HCl → Ca 2+ + 2Cl - + H 2 CO 3 H 2 CO 3 → H 2 O + CO 2 ↑

31. Factors of Soil Formation

32. Factors of Soil Formation, Parent Material These are the types of transported parent material. Residual parent material is residual, i.e., weathered rock. Organic soils don’t fit into this dichotomy.

33. Factors of Soil Formation, Parent Material

34. As the cementing agent (carbonate) dissolves, limestone residue can be any size particulate, from sand to clay. Sandstone give sandy soils but how deep these are depends on how fast the cementing agent dissolves. Shale gives clayey soils.

35. Factors of Soil Formation, Parent Material Soils formed in colluvial parent material are found in landscapes like to right.

36. Factors of Soil Formation, Parent Material These are the three types of alluvial deposits.

37. Factors of Soil Formation, Parent Material These not all that common.

38. Factors of Soil Formation, Parent Material Common and often important in agriculture.

39. Factors of Soil Formation, Parent Material Deposition is greatest near the bank leading to highest elevation. Furthermore, this area of deposition is comparatively high in sand + silt. Thus, since the coarser particles are deposited quickly, deposition from the flood water further away is low in sand + silt and high in clay.

40. Factors of Soil Formation, Parent Material A laterally compressed cross section of the Mississippi River natural levee. Notice any familiar names to the soils? The name comes from some place or geographic feature nearby where the soil was first described.

41. Factors of Soil Formation, Parent Material Another depiction of the Mississippi River natural levee. The course has followed a low position in the landscape, and river sediments have been deposited in the channel and outside it, the latter creating the levee.

42. Factors of Soil Formation, Parent Material Apparent old levee, thus earlier course.

43. Factors of Soil Formation, Parent Material

44. These old materials vary in composition depending on their ancient source. Due to uplift or sea level drop, these became exposed and have undergone pedogensis. As with alluvial parent materials (floodplain and deltaic deposits), there are a lot of soils in Louisiana that have formed in marine sediments.

45. Obviously, no.

47. Factors of Soil Formation, Parent Material Partially melted in summer, giving sediment deposited at leading edge or further away. See various topographic features in a glaciated landscape.

48. Factors of Soil Formation, Parent Material None of this in La., however, there are soils in eolian parent material that came from glacial melt. See next slide.

49. Factors of Soil Formation, Parent Material This figure shows loess only to east of river, however, there is loess to the west, just not as much. Also, not nearly as deep in Baton Rouge as further north, like Natchez.

50. Well, not necessarily because there are deposits that are more sandy.

51. Factors of Soil Formation, Parent Material, Misfits

52. This is the general progression.

53. Factors of Soil Formation, Climate Clearly, parent material is the most important of the 5 factors of soil formation. Climate comes in next. Without precipitation (water) and warm temperature, there will not be a lot of plant growth, mineral weathering nor translocation of particulate matter in the profile –thus, pedogenesis is slow.

54. Factors of Soil Formation, Climate Example effects High rain and low temperature (increase / decrease) organic matter High rain (increase / decrease) salt leaching The reason why low temperature leads to accumulation of organic matter is the effect it has on slowing microbial decomposition of organic matter.

55. Factors of Soil Formation, Climate High rain (increase / decrease) clay translocation High rain and high temperature (increase / decrease) mineral weathering

56. represents generally cool and dry climate D is the right choice. If it’s cool and dry there, there hasn’t been a lot of weathering and leaching going on. The opposite would be true for Panama in the next slide.

57. represents generally warm and wet climate

58. Factors of Soil Formation, Climate The 5 factors of soil formation are interrelated to varying extent. In this example, ample water is needed for forest vegetation and jointly due to greater rainfall and specific effect of trees, forest soils are different from prairie soils.

59. Factors of Soil Formation, Organisms

62. The preceding slide was omitted earlier because the explanation is long. It goes like this. Soils are open and leaky systems, at least in humid climates. Thus, soluble substances are leached from them, including nutrient cations, like Ca 2+, Mg 2+ and K +. To some extent these are replaced by deposition from the atmosphere but this is not sufficient to offset natural leaching. To make this matter worse, there is continuous generation of H + in the soil. It comes from CO 2 released in respiration (microbes, roots, etc.) which forms H 2 CO 3, a weak but abundant acid. Furthermore, the decomposition of organic matter in soil results in release of various organic acids (R-COOH) and small amounts of the strong acids, nitric (HNO 3 ) and sulfuric (H 2 SO 4 ). The H + from these acids tends to replace base cations like Ca 2+, Mg 2+ and K + that are adsorbed onto the negatively charged soil colloidal particles (clay and humus), thus acidifying them, and with the bases in solution, they are subject to loss in water that drains through the soil. The net effect is long-term acidification of soil. This is the natural course of things. However, if the base cations, which are nutrients, are taken up in large quantities by plant roots, the acidification process is slowed. Ca 2+ etc. taken up by plants is returned to the soil in litter so that these nutrients are cycled between soil and plant. Some plants, like the deciduous trees compared with coniferous trees, cycle nutrients quickly, thereby more effectively slow soil acidification.

63. Factors of Soil Formation, Organisms So how can a soils guy say that observed differences between two soils are due to one or another of parent material, climate, organisms, topography or time? If the focus is effect of organisms, find 2+ soils that come from the same parent material, formed under the same climate, on the same type of landscape and are about the same age. These 2+ soils would constitute a biosequence of soils.

64. Factors of Soil Formation, Organisms So there you see. The effect of trees has been to cause deeper profile development, greater mineral weathering and greater soil acidification.

65. Factors of Soil Formation, Topography Erosion takes away topsoil. Furthermore, less water infiltrates so there is less translocation of clay to form a clayey B horizon.

66. Factors of Soil Formation, Topography

67. Factors of Soil Formation, Topography It does the this, not the that. Where there is a shallow groundwater table, it tends to roughly parallel the soil surface, but not exactly. The effect of a shallow water table is to impede drainage, thus minimize translocation of particulates through the profile.

68. Factors of Soil Formation, Topography To the left, there is deeper soil development at the top of the hillock but in the lower scenario there may be deeper development on the sides. However, erosion probably comes into play, complicating interpretations.

69. Factors of Soil Formation, Topography Probably more on side away from heat source, lower temperature so slower rate of microbial activity and organic matter decomposition. The low wet spot is prime for accumulation of organic matter since poorer aeration slows overall microbial activity.

70. Factors of Soil Formation, Time

71. Red River soils are somewhat special in that they can have carbonate (from the West Texas, New Mexico, Oklahoma source area) in them. However, it tends to be neutralized and leached with time. So which is oldest and on what levees is it found?

72. Factors of Soil Formation, Time Gallion on abandoned levees and Severn on current levees. Roxanna on both.

74. Factors of Soil Formation, Time

76. Horizon Designations

77. Patrick F. Taylor Hall, alas Horizon Designations

79. The t is for translocated, of course. Not clearly an A or an E but more like an A than an E, etc.