Soil physical and chemical properties the analogy lecture. Beth Guertal Auburn University, AL

Transcription

1 Soil physical and chemical properties the analogy lecture. Beth Guertal Auburn University, AL

2 Soil Physical Properties Porosity Pore size and pore size distribution Water holding capacity Bulk density Texture Hydraulic conductivity Infiltration Layering and compaction layers

3 Porosity The holes in the soil that are filled with air or water. Pore space is typically around 50% of the total soil volume. We separate pores into two size classes: macropores and micropores.

4 Macropores & Micropores Pore Size Distribution Macropores aid in water drainage, greater in sandy and well-aggregrated soils. Micropores water holding capacity, capillary mvt of water, greater in finetextured soils. Would like about half micro- and half macropores in our distribution of pore sizes.

5 How Water Moves Two forces control water movement: 1. Gravity 2. Matric potential aka wicking, capillary action

6 Gravity

7 Capillary Flow

8 Bulk Density Mass of soil divided by the volume that soil occupies Bulk density = Weight of the oven dry soil Volume of soil

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10 1.8 Bulk Density as Affected by Traffic bulk density (g cm -3 ) Jun-97 Jun Relative Level of Traffic

11 You can aerify to reduce soil bulk density Soil bulk density as affected by aerification - loamy sand with Tifway bermudagrass. Oct Aerification? YES NO Nov Bulk density grams per cm a 1.74 b

12 Texture and pore size etc. etc. Texture is the relative percentage of sand, silt and clay.

13 Soil with a high sand content High macropore content. Rapid drainage of water. Less prone to compaction. Low nutrient holding capability.

14 Soil with a high clay content High micropore content. Higher water holding capacity. More prone to compaction. Higher nutrient holding capacity.

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16 Hydraulic Conductivity Quantity of water that flows through a column of soil. We most typically refer to K sat Saturated Hydraulic Conductivity Infiltration Rate at which water enters a soil Infiltration rate time

17 How water moves though soil Unsaturated flow capillary (micro) pores Force of gravity Once soil is saturated gravity predominates

18 Water movement in layered soils

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23 Layered soil profiles

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26 Saturated Hydraulic Conductivity Constant Head method (Klute and Dirksen,1986) TGRU 2000 # Aerifications K sat, in hr a 1 11 b

27 Compaction Relief - Aerification 0 soil resistance (kpa) depth (mm) X X X XY XY X X X SRH No Aerification

28 Compaction Relief - Aerification soil resistance (kpa) depth (mm) XY XY XY X GA60H No Aerification

29 Compaction Relief - Aerification soil resistance (kpa) depth (mm) X X X X X GA60S No aerification

30 Root Weight and Shoot Density AU Practice Field Dry weight of Shoot roots density Trt g core -1 number core -1 SRH 3.9 a c SRS 4.4 a a GA60H 5.3 a bc GA60S 6.0 a 99.8 c Pull Behind 4.8 a a No Aerification 1.6 b bc

31 Soil Chemical Properties Cation exchange capacity Acidic and basic cations base saturation Clays and clay types ph

32 Clays - backbone of soil chemistry the soil colloids very small particle size extremely high surface area carry a charge (can be or -) all of this holds true for OM, too

33 All types of soil clays are constructed from two basic building blocks: silicate tetrahedrons aluminum octrahedrons arrangement of these blocks dictates clay behavior

34 Silica Tetrahedron Silicon Oxygen

35 Aluminum octrahedron aluminum or magnesium oxygen or hydroxy

36 It is the arrangement of these two basic clay building blocks that determines the characteristics of clays

37 1:1 Clays Al octahedron Si tetrahedron Hydroxyl Aluminum Oxygen or Hydroxyl Silicon Oxygen

38 1:1 Clays - Kaolinite When the tetrahedral and octahedral sheets alternate the clay type is a 1:1 clay. Tetrahedral and octahedral sheets in a 1:1 clay are held tightly and no expansion between layers occurs when the clay is wetted. 1:1 clays have a low surface area and relatively small cation exchange capacity.

39 1:1 Clays Kaolinite

40 2:1 Clays tetrahedral layer octahedral layer tetrahedral layer adsorbed cations and water in interlayer tetrahedral layer octahedral layer tetrahedral layer

41 2:1 Clays Expanding Smectite (Montmorillonite) and Vermiculite When clay layers are created by sandwiching an octahedral layer between two tetrahedral layers, and stacking these layers, the clay is a 2:1 clay mineral. The different types are: Smectite, 2) Vermiculite, and, 3) Micas. Smectite and Vermiculite are both EXPANDING 2:1 clays. Such clays swell when wetted, have a high surface area and a high cation exchange capacity due to isomorphic substitution. Smectite will expand the most because water fits into between the layers. Vermiculite will expand less as it has different interlayer characteristics.

42 Vermiculite Montmorillonite

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45 2:1 Clays Non expanding Illite Mica (nonexpanding) will not expand because of potassium ions in the interlayer space, ions which cause the layers to stick together.

46 Product Name: TURFACE MVP Revision Date: 1/1/14 MSDS Number: BLM001 Common Name: N.A. CAS Number: Description: Calcined, non-swelling illite and non-crystalline opal CT mineral.

47 Illite

48 The source of charge in soils Soils have (generally) a net negative charge: Thus, cations ( charge) attach to the soil The net negative charge comes from two things: ph dependent charge (not as much) Clays and organic matter (important) We talk about these negative charges via CEC (cation exchange capacity)

49 How clays get that negative charge: Isomorphous Substitution Al 3 Si 4 net charge = -1 Mg 2 Al 3 net charge = -1

50 The clay type and clay content, and the organic matter content determine the cation exchange capacity (CEC) of a soil. This affects the ability of the soil to retain nutrients.

51 Cation Exchange Capacity Sum total of exchangeable cations that a soil can absorb clay or OM Mg 2 Ca 2 Ca 2 K K Mg 2 K Ca 2 K soil solution

52 NH 4 Soil NH NH 4 4 NH NH 4 4 NH 4 NH 4 K Mg 2 K Ca 2 Ca 2 Na K 1. NH 4 NH 4 NH 4 NH 4 NH 4 NH 4 NH 4 NH 4 NH 4 Mg 2. NH 4 K 2 K Ca 2 Ca Na 2 K K K K K K K K NH 4 NH 4 NH 4 NH 4 NH 4 NH 4 NH 4 NH 4 NH 4 3. NH 4 K K K 4. NH 4 NH 4 NH 4 K K K K K NH 4 NH 4 NH 4 NH 4 NH 4 NH 4 NH 4

53 Typical cation exchange capacities (CEC) and source of the CEC material Total CEC fixed variable cmol/kg organic smectite vermiculite kaolinite USGA greens mix 2 (sand) %

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55 Treatments: Amendment Percentage (by vol) Sand 100 Profile (illite) 50 Profile 25 Clinolite (zeolite) 50 Clinolite 25 Axis (diatomaceous earth) 50 Axis 25 None 0 4 replications of each treatment in a RCB design.

56 Physical Properties of the Amendments Amendment Surface Area - external Surface Area internal Water content at field capacity CEC m 2 /g m 2 /g ml/100 g cmol c /kg Axis Clinolite Profile Peat NA Sand NA

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58 Mehlich Soil-Test Extraction Results after Year 3 Mehlich Extractable soil P, K, Ca and Mg, and soil ph 10 mo. after 3rd incorporation (April, 2007) Trt P K Ca Mg ph lb/a Sand 70 a 50 c 602 ab 68 a 6.0 a Profile (50) 77 a 70 bc 623 ab 77 a 5.9 a Profile (25) 70 a 60 bc 613 ab 71 a 6.0 a Clinolite (50) 76 a 100 a 774 a 77 a 6.1 a Clinolite (25) 80 a 118 a 628 ab 76 a 6.1 a Axis (50) 74 a 56 c 545 b 63 a 5.8 a Axis (25) 77 a 62 bc 593 ab 68 a 5.9 a Nothing 79 a 70 bc 714 ab 81 a 6.0 a

59 Base Saturation nonacid cations: Ca 2, Mg 2, K, Na acid cations: H, Al 3 base saturation = nonacid cations CEC (acid nonacid cations) x 100

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61 Soil Acidity measured via soil ph ph = -log [H ] active acidity : H in soil solution potential acidity : H on CEC, plus nonexchangeable H

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63 Soil Buffering - resistance to change in ph the buffering capacity is considered when determining how much lime must be applied

64 Potential Acidity Active acidity Active acidity are those acidic cations in the soil solution. Potential acidity is the exchangeable acidity (those acidic ions on the CEC) plus residual acidity (nonexchangeable Al and H associated with clays and organic matter).

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66 Lime must neutralize activity acidity and some portion of potential acidity. The buffer ph is used to determine how big that pool of potential acidity is.

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68 All Done!!