Transcript HYDRAULICS_8 - NYF Webmail

IRRIGATION_2
Design of Irrigation Systems
by
László Ormos
Soil properties
Soil texture(water holding capacity)
• Clay
<0.002 mm
• Silt
0.002-0.02mm
• Fine sand
0.02-0.2mm
• Coarse sand
0.2-2mm
• Gravel
>2mm
Sandy clay
Clay
Clay loam
Silty clay
Silty clay loam
Sand
Loamy sand
percent sand
Sandy loam
Loam
Soil texture
Silt loam
Silt
Soil properties
Soil structure (infiltration rate)
Single grains
Prismatic
Platy
Infiltration rate
rapid
(20-100mm/hr)
Infiltration rate
moderate
Infiltration rate
slow
(4-5mm/hr)
Soil-water-plant relationship
Soil moisture
Total water potential acting is as following:
Pt  Pm  Pg  Po  Pp
where
Pt is the total water potential,
Pm is matric potential due to capillary forces,
• adhesion force (attractive force betweenthe solid particle and
the water)
• cohesion force (attraction between water molecules)
Pg is gravitational potential due to the gravity,
Po is osmotic potential due to the dissolved salts in the water,
Pp is pressure potential due to the position with respect to a fixed
datum level.
Soil-water-plant relationship
Classes and availabilities of soil water
Saturation
Field capacity
Available moisture
Gravitational water
Rapid drainage
Capillary water
Slow drainage
Permanent wilting
Unavailable moisture
Hygroscopic water
Essentially no drainage
Soil-water-plant relationship
Suction
Hysteresis effect
Moisture content
Soil-water-plant relationship
The movement of water in the soil
• Hydraulic conductivity (or flow velocity)
 cm 3 
Q

s
H cm 
 cm 


V


KS
2

A cm 
L cm 
 s 
where
Q is the amount of water which moves through the soil,
A is the cross section area of the tested soil sample,
H is the difference in water pressure head between two points,
L is the distance between the two points,
KS is the Darcy coefficient of proportionality.
Soil-water-plant relationship
KS in saturated soil is the following:
 cm  L cm 

V
KS
 s   H cm 


KnS in unsaturated soil is the following:
 cm 
V

 s 
K nS  H  
hG
where hG is the hydraulic gradient computed as follows:
hG 
H 2 cm   H 1 cm 
L cm 
H1 and H2 are pressure head values.
Soil-water-plant relationship
Infiltration under various methods of irrigation
• Furrow irrigation: gravitational influence,
• Flood irrigation: gravitational influence,
• Sprinkler irrigation: water distribution is more or less symmetrical,
• Micro-sprinkler: the distribution pattern is trapezoid, and wets the
area only partially (50-70%),
• Drip irrigation: cone-shaped volume of moistured soil surrounding the
plant root-zone, size and shape depend on the type
of soil, the discharge of dripper, and the duration of
water application.
Soil-water-plant relationship
Root distribution in the various
soil layers
0
3
7.4%
40%
30%
20%
10%
Soil depth [cm]
68.7%
D/4 D/4 D/4 D/4
Root zone extraction
Depth D
Water distribution in the soil
10
10.3%
20
9.4%
30
4.2%
40
Soil-water-plant relationship
Storage in soil
• Small pores are required to store the water.
• Medium-sized pores help the movement of water in the soil.
• Large-sized pores are required for aeration of soil.
The saturation
• Saturation capacity means the pores of soil are full filled with water.
• Gravity occurs the water drains quickly from the root zone.
Soil-water-plant relationship
Field capacity Fc
•
•
The moisture content of soil means the remained water quantity after the
gravitational water has been removed.
Field capacity depends on the texture of soil.
Permanent wilting point Pw
•
•
•
It is the minimum of the available moisture of soil.
When water content is at the wilting point or it is lower then plants
permanently wilt and they might not be recovered after being placed in
moisturized environment.
Wilting point is influenced by soil texture.
Temporary wilting point
•
It is occurred in any hot windy days but plants will recover in cooler portion
of days.
Soil-water-plant relationship
Available soil water AW
 g 
 S  3
 cm 
AW %    F C %   P W %  
 g 
 W  3
 cm 
where AW is in percent of moisture volume, S is the specific density
of soil and W is the specific water density.
The depth of available soil water for a 1m layer AWDm
 g 
 S  3
 mm 
 cm 








AWDm 

AW
%

10

%

%

 10
F
P
C
W

 g 
 m 
 W  3
 cm 
Soil-water-plant relationship
The depth of available water in the soil layer of depth Z AWDZ
 mm 
 mm 
AWDZ 
 Z m 
  AWDm 

 m 
 Z m  
where Z means the soil layer of depth.
The available water volume in the soil layer of depth Z AWVZ
3


 mm 
m
AWVZ 
  AWDZ 
  10
 ha  Z m  
 Z m  
Soil-water-plant relationship
The depth of available water in the main root zone Zr of the
crop AWDZr
 mm 
 mm 
AWDZr 
 Zr m 
  AWDm 

 m 
 Z m  
where Zr is the depth of main root zone.
After replacement in this equation, calculation directly the
depth of available water in the main root zone is as follows:
 g 
 S  3
 mm 
 cm 






AWDZr 

%

%

 Zr m   10
FC
PW

 g 
 Zr m  
 W  3
 cm 
Soil-water-plant relationship
The available water volume in the main root zone Zr of the
crop in a hectare AWZr
3


 mm 
m
AWVZr 
  AWDZr 
  10
 ha  Zr m  
 Zr m  
The net water application NWA
NWA mm   AWDZr
mm   PWD % 
where PWD is the permitted water deficit.
The available net water application in the main root zone Zr
of the crop in a hectare AWZr
3


m
NWA 
  NWA mm   10
 ha  Zr m  
Soil-water-plant relationship
The gross water application GWA
GWA mm  
NWA mm 
 irr
where irr is the efficiency of irrigation.
The irrigation interval IrI
IrI days  
NWA mm 
 mm 
CU 

day


where CU may be either the consumptive use, or evapotranspiration.
Soil-water-plant relationship
Calculate the available water volume per hectare in a soil
with a homogeneous profile according to the following data:
•
•
•
•
•
Field capacity
Wilting point
Soil density
Water density
Main root zone
Fc=17[%]
Pw=7 [%]
S=1.3[g/cm3]
W=1.0[g/cm3]
Zr=0.4[m]
Soil-water-plant relationship
1.
2.
Available water by volume:
 g 
1 .3 
3
S
 cm 
AW v %    F C  P W  
 17 [%]  7 [%]  
 13 [%]
 g 
W
1
3
 cm 
The depth of available water for a 1m layer:
 mm 
 mm 




AWDm 

AW
%

10

13
%

10

130

 m 
 m 


3.
The depth of available water in the effective root zone Zr:
 mm
 mm 
 mm 
AWDZr 
 Zr m   130 
  AWDm 

 m
 m 
 Zr m  

  0 . 4 m   52 mm 

Soil-water-plant relationship
4.
The available water in a hectare, in the effective root zone Zr:
3


 m3 
m
AWVZr 
  AWDZr mm   10  52 mm   10  520 



ha

Zr
m
ha




Soil-water-plant relationship
Calculate the available water volume per hectare in a soil with different
texture layer according to the following data:
Layer
Fc
Pw
S
[%w]
[%w]
[g/cm3]
Sandyloam
13
5
1.5
0.15
loam
20
8
1.4
35-65
0.30
Clayloam
27
13
1.4
65-110
0.45
clay
32
16
1.3
Layer
Depth
Layer
thickness
[cm]
[m]
1
0-20
0.2
2
20-35
3
4
Soil
texture
Soil-water-plant relationship
The applied equation is
 g 
3
 mm 
 cm 
AWDZr 
 Zr m   10
   F C %   P W %  
 g 
 Zr m  
 W  3
 cm 
S
Fc-Pw
[%]
S
[g/cm3]
Zr
[m]
AWDZr
[mm/layer]
13-5
1.5
0.2
24.0
20-8
1.4
0.15
25.2
27-13
1.4
0.3
58.8
32-16
1.3
0.1
20.8
AWDZr (Zr=0.75m)
128.8
References
Azenkot, A.(1998):”Design Irrigation System”. Ministry of Agriculture Extension Service (Irrigation Field service), MASHAV Israel
Dr. Avidan, A.(1995):”Soil-Water-Plant Relationship”. Ministry of
Agriculture Extension Service (Irrigation Field service), CINADCO,
Ministry of Foreign Affairs, MASHAV, Israel
Sapir, E.-Dr. E. Yagev (1995):”Drip Irrigation”. Ministry of Agriculture and Rural Development, CINADCO, Ministry of Foreign Affairs,
MASHAV, Israel
Sapir, E.-Dr. E. Yagev (2001):”Sprinkler Irrigation”. Ministry of culture and Rural Development, CINADCO,Ministry of Foreign
Affairs, MASHAV, Israel
Eng. Nathan, R. (2002):”Fertilization Combined with Irrigation
(Fertigation)”. Ministry of Agriculture and Rural Development,
CINADCO,Ministry of Foreign Affairs, MASHAV, Israel