irrigation_2 design of irrigation systems by lászló ormos

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


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


Hysteresis effect

Moisture content

Suc

tion


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


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


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


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.


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.


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


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


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


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


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


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]


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


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

103

mmAWDZrmZrha

mAWVZr

hammm3

5201052


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


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

irrigation_2 design of irrigation systems by lászló ormos

Documents

pores of soil

water distribution

soil depth

type of soil

unsaturated soil

aeration of soil

movement of water

soil root distribution