CROP WATER REQUIREMENTS FOR MICROIRRIGATION SYSTEM DESIGNcwc.gov.in/main/Download_Index/Crop Water...

CROP WATER

REQUIREMENTS FOR

MICROIRRIGATION SYSTEM

DESIGNManoj Khanna

Principal Scientist &

In Charge Farm Operation Service Unit (FOSU)

Water Technology Centre

ICAR-Indian Agricultural Research Institute

New Delhi

CROP WATER REQUIREMENT ESTIMATION

USING CROPWAT

Crop Water Requirement

Crop water requirement (WR) is the quantity

of water utilized by a crop, irrespective of its

source for obtaining maximum yield in a

particular area without any/minimum

adverse effect on soil properties.

CWR = Etc/CU + Unavoidable application losses + Special operation needs

CWR = Irrigation + Effective rainfall + Gr water contribution + Change in

soil water storage


USING CROPWAT

Crop Evapotranspiration (Etc)

Etc = Eto x Kc

Eto: Reference Evapotranspiration is estimated based on

climatic data of the place

It is estimated using Modified Penman Monteith Method

(Details can be seen in FAO Irrigation and Drainage Paper 56)

Kc: Crop factor (based on crop growth stage)


USING CROPWAT

Input Data Required

Monthly/Daily Climatic data

Minimum/Maximum Temperature

Relative Humidity

Sunshine duration

Wind Speed

Radiation

Rainfall (Effective Rainfall)

Crop data

Crop duration (sowing/harvesting date)

Crop factor

Root zone depth

Soil Data

Soil Type

Water holding capacity (Field Capacity/wilting Point)


USING CROPWAT

Effective Rainfall Based on

Fixed Percentage

Dependedable rain formula given by FAO

Empirical formulas

USDA Soil Conservation Service Formula

Not included in Irrigation requirement


USING CROPWAT

Irrigation Scheduling

Based on

Fixed depletion percentage

Irrigate at fixed interval (Frequent irrigation

in microirrigation)

Irrigate at critical stages


USING CROPWAT

Irrigation Efficiency

Surface Irrigation: 50%

Sprinkler Irrigation: 80%

Drip Irrigation: 90%

Irrigation Schedules/Planning

Develop indicative irrigation schedules to improve water

management

Evaluate the current irrigation practices and their

associated crop water productivity;

Evaluate crop production under rainfed conditions and

assess feasibility of supplementary irrigation;

Develop alternative water delivery schedules under

restricted water supply conditions.

Irrigation Schedules/Planning

Rainfall

Water stress coefficient (Ks)

Crop Etc

Root zone depletion

Net irrigation

Deficit: amount of water (in mm) below field

capacity

Irrigation losses

Gross irrigation

Flow

Soil Water Balance


USING CROPWAT

Demonstration of FAO CROPWAT 8.0 for

windows with example

Demonstration of FAO CLIMWAT 2.0

Irrigation Methods

(Pressurized) Drip

Sprinkler

Micro sprinkler

Characteristics

Low flow requires good filtration

Reduced application losses

Reduced runoff

Controlled application

Typical Layout of Drip Irrigation-Fertigation System

Drip irrigation in potato

Crop Increase

in yield,

%

Water

saving,

%

Tomato 25-50 40-60

Onion 25-40 20-30

Potato 20-30 40-50

Cabbage 30-40 50-60

Cauliflower 60-80 30-40

Drip irrigation in Tomato Drip irrigation in Onion Drip irrigation in Cabbage

Drip irrigation in Cauliflower

INCREASE IN YIELD AND WATER SAVING THROUGH DRIP

IRRIGATION IN COMPARISON TO CONVENTIONAL

SURFACE IRRIGATION METHODS IN VEGETABLE CROPS

Components of Drip Irrigation

System

Main line HDPE/ PVC

Sub main line HDPE/ PVC

Laterals LLDPE/ LDPE

Emitters Line source/ Point Source/ Disk Source

Control system Filters/ Controllers

Fertigation system Tanks/ Venturi System

Advantages of Drip Irrigation

System

Better Soil water regime for higher crop yield

Water and Fertilizer savings

Less labour intensive

Land levelling not required

Minimal weed problem

Automatic control is possible

Less incidence of pest and diseases

Adaptability and Limitations of Drip

Irrigation System

All Types of fruits, vegetables, vines, cotton,

sugarcane

Arid and semi-arid areas

Hilly areas, Coastal, Waste lands

Operational problems such as clogging

High initial cost

Higher Skill s required for operation

Adaptability

Limitations

Pump set

Main Line

Sub Main

Line

Emitter

Lateral Line

Layout of drip irrigation system

Design of Drip Irrigation Systems

Design Steps

Crop Water Requirement (Monthly, Litres)

NAKKE V pcp

V = Volume of water required (litres)

Ep = Mean pan evaporation for the month (mm/day)

Kc = Crop factor

Kp = Pan factor

A = Area to be irrigated (Sq.m.)

N = Number of days in a month


Design Steps


ARVV en Net Volume of water

to be applied=

Where, Re = Effective rainfall (mm)


Design Steps Crop Water Requirement (Monthly, Litres)

Number of operating hours

of System during a month (T)=

Where, Wp = percentage wetting

edischdripperPlantsofNoplantperdrippersofNo

WVT

pn

arg..


Design Steps


Number of operating hours of

System per application (Tm)=

Where, Nm = Number of application per month

mN

T

Hydraulic Design of Drip Irrigation

Systems

The flow through nth section of pipe given

by

Where:

qi = discharge from each emitter LPH;

Qn= flow passing through nth section LPH;

m= total number of emitters in lateral line;

i= emitter number in lateral line

m

ni

in qQ

m

ni

in qQ


Systems

The characteristics of flow (laminar or turbulent)

are identified by Reynolds’s number which is

given by

Where:Vn = Mean velocity of flow through the nth section of

pipe, m/sec;

D = inner diameter of pipe, m;

= kinematic viscosity of water in m2/sec

Laminar flow Ren<2000

Turbulent flow Ren> 2000

m

ni

in qQ

DVn

n Re


Systems

Head loss for pipe flow in both laminar and

turbulent range is given by

Where:

Fn = head loss due to friction in nth section of line

fn = friction factor in nth section of line

L = length of nth section of line

G = acceleration due to gravity

Laminar flow Turbulent flow

m

ni

in qQ

gD

VLfF

nn

n2

2

n

nfRe

64

25.0Re

316.0

n

nf


Systems

Cumulative friction head loss F for pipe flow in

lateral or main line is given by

m

ni

in qQ

n

n

nFF1

CROP WATER REQUIREMENTS FOR MICROIRRIGATION SYSTEM DESIGNcwc.gov.in/main/Download_Index/Crop Water...

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