irrigation_2 design of irrigation systems by lászló ormos
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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 pe
rcen
t cla
y
percent sand
percent silt
Soil texture
Sand
Loamy sand
Sandy loam Loam Silt loam Silt
Silty clay loam
Silty clay
Clay loam
Clay
Sandy clay
Soil properties
Soil structure (infiltration rate)
Single grainsInfiltration rate
rapid (20-100mm/hr)
PlatyInfiltration rate
slow (4-5mm/hr)
PrismaticInfiltration rate
moderate
Soil-water-plant relationship
Soil moistureTotal water potential acting is as following:
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.
PpPoPgPmPt
Soil-water-plant relationship
Classes and availabilities of soil water
Saturation
Field capacity
Permanent wilting
Gravitational waterRapid drainage
Capillary waterSlow drainage
Hygroscopic waterEssentially no drainage
Available moisture
Unavailable moisture
Soil-water-plant relationship
Hysteresis effect
Moisture content
Suc
tion
Soil-water-plant relationship
The movement of water in the soil• Hydraulic conductivity (or flow velocity)
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.
KcmL
cmH
cmA
scmQ
s
cmV S
2
3
Soil-water-plant relationship
KS in saturated soil is the following:
KnS in unsaturated soil is the following:
where hG is the hydraulic gradient computed as follows:
H1 and H2 are pressure head values.
cmH
cmL
s
cmVK S
hGscm
VHK nS
cmL
cmHcmHhG 12
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 relationshipR
oot
zone
ext
ract
ion
Dep
th D 40%
30%
20%
10%
D/4
D/4
D/4
D/4
10
30
20
30
40
Soi
l dep
th [
cm]
7.4%
68.7%
10.3%
9.4%
4.2%
Water distribution in the soil Root distribution in the various soil layers
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
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
cm
gcm
g
PFAW
W
S
WC
3
3
%%%
10%%10%
3
3
cm
gcm
g
PFAWm
mmAWDm
W
S
WC
Soil-water-plant relationship
The depth of available water in the soil layer of depth Z AWDZ
where Z means the soil layer of depth.
The available water volume in the soil layer of depth Z AWVZ
mZm
mmAWDm
mZ
mmAWDZ
103
mZ
mmAWDZ
mZhamAWVZ
Soil-water-plant relationship
The depth of available water in the main root zone Zr of the crop AWDZr
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:
mZrm
mmAWDm
mZ
mmAWDZr
10%%
3
3
mZr
cm
gcm
g
PFmZr
mmAWDZr
W
S
WC
Soil-water-plant relationship
The available water volume in the main root zone Zr of the crop in a hectare AWZr
The net water application NWA
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
103
mZr
mmAWDZr
mZrhamAWVZr
%PWDmmAWDZrmmNWA
103
mmNWAmZrha
mNWA
Soil-water-plant relationship
The gross water application GWA
where irr is the efficiency of irrigation.
The irrigation interval IrI
where CU may be either the consumptive use, or evapotranspiration.
irr
mmNWAmmGWA
daymm
CU
mmNWAdaysIrI
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 Fc=17[%]• Wilting point Pw=7 [%]• Soil density S=1.3[g/cm3]• Water density W=1.0[g/cm3]• Main root zone Zr=0.4[m]
Soil-water-plant relationship
1. Available water by volume:
2. The depth of available water for a 1m layer:
3. The depth of available water in the effective root zone Zr:
W
SWC PFvAW %
10%
AWm
mmAWDm
mZrm
mmAWDm
mZr
mmAWDZr
[%]131
3.1[%]7[%]17
3
3
cm
gcm
g
m
mm13010%13
mmmm
mm524.0130
Soil-water-plant relationship
4. The available water in a hectare, in the effective root zone Zr:
103
mmAWDZrmZrha
mAWVZr
hammm3
5201052
Soil-water-plant relationship
Calculate the available water volume per hectare in a soil with different texture layer according to the following data:
Layer Layer
Depth
Layer thickness
Soil texture
Fc Pw S
[cm] [m] [%w] [%w] [g/cm3]
1 0-20 0.2 Sandy-loam
13 5 1.5
2 20-35 0.15 loam 20 8 1.4
3 35-65 0.30 Clay-loam
27 13 1.4
4 65-110 0.45 clay 32 16 1.3
Soil-water-plant relationship
The applied equation is
10%%
3
3
mZr
cm
gcm
g
PFmZr
mmAWDZr
W
S
WC
Fc-Pw[%]
S[g/cm3]
Zr[m]
AWDZr[mm/layer]
13-5 1.5 0.2
20-8 1.4 0.15
27-13 1.4 0.3
32-16 1.3 0.1
AWDZr (Zr=0.75m)
24.0
25.2
58.8
20.8
128.8
References
Azenkot, A.(1998):”Design Irrigation System”. Ministry of Agricul-ture 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 Agricul-ture 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