This presentation is depicting soil colour aspects and its estimation and different types of water

2. SOIL PROFILE

6. • It is the dominant
spectral color.
• It is arranged radially
from one arid to next
card.
• The symbol is the letter
of abbreviation of
rainbow (VIBGYOR)
proceeded by numbers
from 0 to 10.

7. • It is the measure of
intensity of light.
• The notation consists of
numbers from 0 to 10,
where 0 is for absolute
black and 10 is for
absolute white.
• It is vertically arranged.
• The color becomes
successively lighter from
bottom of card to top and
value increases .

8. • It is the relative purity
of the light.
• Its notation consists of
numbers beginning at 0
for grey and increases
with decrease in
grayness.

14. Soil water

22. Types of water in soil:
HYGROSCOPIC WATER
– Adhesion water
– Remove by oven drying
– Not available to plants

24. 2. CAPILLARY WATER
– Cohesion water
– Remove by air drying
– Most is available to plants
• some unavailable to plants (especially in clay or high
OM soils)
– 15 – 20 molecules thick

26. Difference between wilting point and hygroscopic
coefficient:
Moist Dry to touch
Can’t squeeze water Air-dried
Plant can’t get water Can be oven dried to
remove water
at wilting
point
at hygroscopic
coefficient

27. 3. Gravitational water
– Not available to plants
– Drains through soil under influence of gravity
– Through large pores
• Small pores can hold water against pull of gravity
through capillarity

29. Gravitational
water
Plant-available
Water
(capillary)
Plant-unavailable
water
(capillary)
Adhesion
water
Field capacity
Wilting pointHydroscopic
coefficient
Oven
dry
No water
(Air dry)

30. CAPILLARITY
Height water will
rise in cylinder
depends on
diameter of tube;
due to adhesion of
water and tube
Plastic Glass

31. CRITICAL LEVELS OF WATER IN SOIL:
• Field capacity
• Wilting point
• Hygroscopic coefficient

32. Field Capacity
• Amount of water in soil after free drainage has
removed gravitational water (2 – 3 days)
• Soil is holding maximum amount of water
available to plants
• Optimal aeration (micropores filled with
water; macropores with air)

34. Wilting Point
• Amount of water in soil
when plants begin to
wilt.
• Plant available water is
between field capacity
and wilting point.

35. Hygroscopic coefficient
• Amount of moisture in air dry soil
• Difference between air dry and oven dry
amounts

36. Not all capillary water is equally available to plants
• Plants can extract water easily from soils that
are near field capacity
• Wilting point is not the same for all plants
– Sunflowers can extract more water from soil than
corn

38. Wilting point Field Capacity
Adhesion water
Micropores full;
macropores have air
Gravitational water
All pores full

39. Hydraulic pressure of soil water
• Pressure = force / area
Open body of water
“0”
at surface
increases with
depth
Hydraulic pressure

40. • Same in saturated soil
“0”
at surface
increases with depth

41. Capillary pressure
• Thin tube in open pan water
Pressure in tube
decreases away
from water surface
0
-10
-20 g/cm3
(Adhesion to walls of tube;
cohesion in center of tube;
therefore thin tube only)

42. Same in unsaturated soil:
• Capillary water is water in small pores
continuously connected to free water surface
(soil water table)
Capillary water
(continuous film)
Soil water table
Saturated soil
0
-10
-20
+10

43. • the smaller the pore space, the higher
capillary water will rise in profile
• Smaller pore space, tighter water is held to
particle surfaces against gravity (i.e., higher
field capacity)
Pan of water
clay silt sand

44. at
• Insert Fig 9.6

45. Energy status of soil water
• Energy status
– Things move to lower energy states
• It takes work to keep them from doing so
– E.g. keeping something from falling in response to gravity
– Influences water movement
• E.g. adhesion attracts water to soil particles so particles
close to soil are at lower energy state

46. Forces on soil water:
• Adhesion
– Attracts water to soil particles
• Holds adhesion(hygroscopic) water and cohesion
(capillary) water
– Called “matric force”
• Ions in solution
– Attracts water to ions
– Called “osmotic force”
• Gravity
– Pulls water downward
– “gravitational force”

47. • Soil water potential
– Amount of work required to move water
– Expressed in bars or Pascals
– Similar to soil water tension

48. Water is held at various tensions/attractions

49. potentials
Water is removed by various potentials

50. • Water moves from areas of higher water
potential (wetter) to areas of lower water
potential (drier).

51. Potentials
• Matric
• Gravitational
• Hydrostatic
• Osmotic
• Total

52. Matric potential
• Work required to remove water held by
adhesion to soil surface and cohesion in
capillary pores.
– Hygroscopic and capillary water
– Zero (if saturated) or negative

53. Gravitational potential
• Work required to draw water down in
response to gravity
– Applies to gravitational water only
– Increases with increasing elevation above soil
water table
• Positive

54. Hydrostatic Potential
• Work required to move water below the water
table; applies only to saturated conditions

55. Osmotic potential
• If there are solutes in the solution, water will
group around them and reduce the freedom
of water movement, i.e., lowering the
potential.

56. Osmotic potential
• Water containing salts is less able to do work than
pure water
– e.g., cannot boil at standard boiling point
• The more salts, the lower (higher absolute value) the
potential
– negative
• Important for plant uptake
– In salty soil, potential in soil solution may be lower than
inside plant root cells, impeding ability of water to pass
into plant

57. Total water potential=
Matric + osmotic + gravitational + hydrostatic

58. • Unsaturated flow: water movement in soils at
less than saturation
– Water moves in response to water potential
gradient (high to low)
• Saturated flow: moves according to
gravitational potential only

59. Hydraulic conductivity
• Ability of a soil to transmit water
• Depends on :
– Pore size
• Coarse grained soil has higher cond. than fine-grained
because movement through large pores is faster
– Amount of water in soil
• Cond. decreases as water content increases
– Water moves through largest pores first