IRRIGATION_2

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IRRIGATION_2

• Design of Irrigation Systems
• by
• László Ormos

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Soil properties

• Soil texture(water holding capacity)
• Clay lt0.002 mm
• Silt 0.002-0.02mm
• Fine sand 0.02-0.2mm
• Coarse sand 0.2-2mm
• Gravel gt2mm

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Soil properties

• Soil structure (infiltration rate)

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Soil-water-plant relationship

• Soil moisture
• Total 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.

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Soil-water-plant relationship

• Classes and availabilities of soil water

Available moisture
Unavailable moisture
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Soil-water-plant relationship

• Hysteresis effect

Suction
Moisture content
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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.

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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.

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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.

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Soil-water-plant relationship
Water distribution in the soil
Root distribution in the various soil layers
40
D/4
Root zone extraction Depth D
30
D/4
20
D/4
10
D/4
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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.

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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.

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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

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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

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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

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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

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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.

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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 Fc17
• Wilting point Pw7
• Soil density ?S1.3g/cm3
• Water density ?W1.0g/cm3
• Main root zone Zr0.4m

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Soil-water-plant relationship

• Available water by volume
• The depth of available water for a 1m layer
• The depth of available water in the effective
  root zone Zr

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Soil-water-plant relationship

• 4. The available water in a hectare, in the
  effective root zone Zr

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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
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Soil-water-plant relationship

• The applied equation is

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 (Zr0.75m)
24.0
25.2
58.8
20.8
128.8
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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