HOW WATER MOVES IN SOIL Beth Guertal Auburn University

Transcription

1 HOW WATER MOVES IN SOIL Beth Guertal Auburn University

2 What s Up for Today Terms associated with water movement in soil. How things in sports field construction/remediation can affect water movement. How you can affect that.

3 What Makes Water Special

4 Hydrogen Bond

5 The Polarity of Water: The Hydrogen Bonds. Many unique properties of water are due to the hydrogen bonds. Ice floats because hydrogen bonds hold water molecules further apart in a solid than in a liquid. Unique physical properties: high heat of vaporization, strong surface tension, nearly universal solvent properties of water are also due to hydrogen bonding. The hydrophobic effect, or the exclusion of compounds containing carbon and hydrogen (nonpolar compounds) is another unique property of water caused by the hydrogen bonds.

6 The Properties of Water that are Important for Soil 1. Cohesion (water molecules attracted to each other) 2. Adhesion (water molecules attracted to a soil surface) Surface Tension (cohesion, liquid-air interface) Capillary rise (adhesion, surface tension) Capillary rise is inversely proportional to a tube radius and liquid density. h = 0.15/r (cm) where: h = height of rise r = radius of tube

7 Surface tension (Cohesion water molecules attracted to each other)

8

9 Cohesion water molecules attracted to each other

10

11 Adhesion attraction of water molecules to a surface Adhesion and surface tension cause water to move up a column.

12 Smaller the pore size (narrower the diameter of the tube) the higher the rise of the water.

13 What Makes Water Move? There are really four things we talk about (in soil physics we call it potential ) 1. Gravity 2. Matric (capillary, suction) 3. Submergence 4. Osmosis

14 Submergence This is a positive pressure due to the weight of water in saturated soils and aquifers. This is the water below the water table (springs, aquifers). An artesian aquifer is a confined aquifer containing groundwater under positive pressure.

15 Osmotic Potential Semi-permeable membrane, such as in plant cells, for osmotic potential to matter. Osmosis movement across a semi-permeable membrane.

16 Gravity The force of gravity acts on soil water the same as any other body. Attraction towards the center of the earth pulls water down.

17

18 Matric (Suction, Tension, Capillary, Pressure) Due to the attractive forces between the water and the soil solids (adhesion). In the most correct sense we measure it as a negative. Often, we drop the negative for ease of use.

19 Pore Size and Water Macropores aid in water drainage, greater in sandy and well-aggregrated soils. Micropores water holding capacity, capillary mvt of water, greater in fine-textured soils. Often called capillary pores. This is related to soil texture sands have more macropores and clays an d soil with organic matter have more micropores.

20 SO Macropores gravity drainage Micropores suction, tension, capillary water holding capacity

21 Where we see these terms in turfgrass management. Macro Micro

22 Capillary Flow

23 So, for water movement in SOILS Gravity And Matric (pressure, suction, capillary)

24 How soil water content changes as a soil dries Drier >

25 Descriptions of Soil Wetness The soil moisture curve (as shown in previous slides) is a continual curve. However, we have distinct points along that curve that we like to use as indicators of the degree of soil wetness. Sort of like a highway is a continual road from one place to another, but you have distinct stops at certain places along that road.

26 Descriptions of Soil Wetness Saturated all soil pores filled with water, volumetric water content close to the total porosity. Gravitational water water is in the macropores, but it begins to percolate downward under the force of gravity. Field capacity the point at which the macropores have drained and are now filled with air. The micropores still hold water which is largely plant available. We use this term a lot.

27 How Water Flows Through Soil Saturated flow all pores, large and small, are filled with water flow is largely controlled by gravity. Unsaturated flow flow in water in which all the pores are not filled with water, this is capillary flow, mainly. Much harder to describe and measure. That is why many of our measurements of water flow are most often done under saturated conditions.

28 Other terms for Water Movement: Infiltration and Percolation Infiltration -the downward entry of water into the soil Infiltration rate: Infiltration/time; decreases with time (initially fast, then slows as soil becomes saturated) Percolation: downward movement of water through the soil (usually saturated conditions) Infiltration is the entry of water at the surface, while percolation is the movement down through the soil. Many use percolation as the same thing as saturated hydraulic conductivity.

29 Measuring Saturated Hydraulic Conductivity (Ksat)

30 Saturated Hydraulic Conductivity Constant Head method (Klute and Dirksen,1986) Sandy loam soil # Aerifications K sat, in hr a 1 11 b

31

32 Water movement in layered soils

33

34

35 How to fix this in real life soils Aerify Get drainage Eliminate layers

36

37 Amendment Inclusion Study Installed each June in 2004, 2005 and 2006 in 5 x 10 foot plots. Saugahactee CC, Auburn, AL. Tifdwarf hybrid bermudagrass P. rye overseeding each Fall.

38 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

39 Double-ring infiltration measurements, in the field. August 30th, (Two mo. after 2 nd application) Trt in/hr Sand Profile (50) Profile (25) Clinolite (50) Clinolite (25) Axis (50) Axis (25) Nothing 3.0 a 2.4 a 2.8 a 2.2 a 3.4 a 3.4 a 2.2 a 3.4 a

40 Laboratory hydraulic saturated conductivity measurements Trt Sept 04 Nov 05 Mar 05 inches/hour Sand 16 a 18 ab 10 ab Profile (50) 13 a 14 ab 11 ab Profile (25) 11 a 11 b 7 ab Clinolite (50) 12 a 23 ab 12 ab Clinolite (25) 14 a 12 b 14 a Axis (50) 14 a 24 a 13 ab Axis (25) 10 a 15 ab 6 b Nothing 11 a 14 ab 8 ab

41 Water Drop Penetration Test

42 Trt Time (seconds) for the water droplet to penetrate the core, by depth (cm) at thatch 1 cm 2 cm 3 cm 4 cm 5 cm 6 cm Feb Control 118 a 64 a 32 a 1.1 ab 0.8 ab 0.9 a 0.9 ab ACA b 21 b 1.7 c 0.4 b 0.4 ab 0.4 a 0.5 b ACA b 24 b 16 abc 0.4 b 0.3 b 0.4 a 0.8 ab ACA b 36 b 13 bc 1.0 ab 0.9 a 1.2 a 1.5 a ACA b 27 b 8 bc 3.8 ab 0.6 ab 0.8 a 1.1 ab ACA b 28 b 16 abc 8.0 a 0.5 ab 0.4 a 0.6 b ACA b 25 b 15 abc 1.6 ab 0.5 ab 0.4 a 0.6 b ACA a 27 b 27 ab 3.1 ab 0.8 a 1.3 a 0.9 ab

43 Thank You.