Irrigation involves applying water to crops to supplement rainfall and meet crop water needs. The key objectives of irrigation are to ensure sufficient soil moisture for plant growth, provide drought protection for crops, and create a favorable environment for plants. Irrigation maximizes crop yields and land productivity, ensuring food security and promoting regional economic development through agriculture and related industries.
Crop water requirement depends on transpiration, evaporation, plant water use, and other losses like conveyance and runoff. It varies based on crop type and growth stage, soil properties, climate factors like temperature and rainfall, and agronomic management practices. Irrigation requirement refers to the water needed beyond effective rainfall and soil moisture. Net irrigation requirement is the amount needed to bring the soil to field capacity, while gross requirement includes application and distribution losses. Irrigation frequency and period depend on the crop's water uptake rate and the soil's moisture supply capacity.
The document discusses the relationship between soil, water, and plants. It covers several key topics:
1. Water plays a vital role in soil functioning, plant growth processes like photosynthesis and transpiration, and is essential for plant cell structure.
2. Water moves through the soil to plant roots through both capillary action and root growth into moist soil areas.
3. Plants absorb water through both passive uptake driven by transpiration pull and active uptake requiring energy when salt concentrations are high.
4. Nutrient movement from soil to roots occurs through mass flow, diffusion, and root interception, and is influenced by soil, plant and nutrient properties.
Bunds are embankment structures constructed across land slopes to obstruct surface runoff. There are two main types: contour bunds and graded bunds. Contour bunds have no longitudinal slope and are suitable for areas with annual rainfall under 600 mm and permeable soils with slopes less than 6%. Graded bunds have a slope to safely dispose of excess runoff and are recommended for high rainfall regions and impermeable soils. The design of bunds considers factors like rainfall, soil type, slope, spacing between bunds, size, length, and area lost due to construction.
check basin , furrow and border strip methodVidhi Khokhani
This document discusses three types of surface irrigation methods: border strip irrigation, check basin irrigation, and furrow irrigation. For each method, it describes what it is, when it is used, and key design aspects. Border strip irrigation uses long, graded strips separated by bunds to guide water down a field. Check basin irrigation uses rectangular plots surrounded by levees to pond water for crops that require submergence. Furrow irrigation uses small channels between ridges to irrigate row crops. The document provides details on layout, sizing, construction, and maintenance considerations for each method.
This document discusses soil water systems and properties. It defines key terms like field capacity, permanent wilting point, and available water. Soil water can exist as gravitational, capillary, or hygroscopic water. The water holding capacities of soils are expressed as constants like saturation capacity, field capacity, and permanent wilting point. These constants can be expressed as either percentages of water held or depth of water stored in the root zone. Plants extract most water from the upper layers of their root zone, with uptake decreasing with depth.
Hydrologic cycle and field water balance dathan cs
The document discusses the hydrologic cycle and field water balance. It provides details on:
1) The hydrologic cycle, which describes the circulation of water between the atmosphere, land, oceans and biosphere through processes like evaporation, condensation, precipitation, and runoff.
2) Components of the hydrologic cycle like green water, blue water, infiltration, recharge, and groundwater flow.
3) The field water balance accounts for all water inputs, outputs, and storage within a soil area over a period of time based on the law of conservation of mass. It considers precipitation, runoff, evapotranspiration, and changes in water storage.
This document provides an overview of soil-plant-water relationships and irrigation water management. It discusses key topics like soil properties that influence water retention and movement, including texture, structure, and density. It describes the different types of water movement in soil like infiltration, percolation, and saturated vs. unsaturated flow. The relationships between soil water tension, moisture content, and pF curves are also summarized. The document aims to explain the important concepts needed to effectively plan and manage irrigation systems.
QUALITY OF IRRIGATION WATER AND MANAGEMENT OF SALINE WATER FOR IRRIGATION
GOVARDHAN LODHA
Enroll. No. (160111017)
Department of Agronomy
M.Sc. (Ag) Agronomy 2nd semester
This document provides information on salinity management of irrigation water. It discusses several methods for managing salinity problems, including drainage to control water tables, leaching salts below the root zone, developing crop tolerance, optimizing cultural practices like irrigation timing, and changing or blending water sources. Drainage systems are shown to effectively reduce soil salinity and improve crop yields over time. Leaching requirements and crop tolerance data help determine appropriate irrigation amounts. Certain cultural practices like land grading and post-sowing irrigation can also improve crop establishment under saline conditions. The objective is to maintain acceptable crop yields through various salinity control strategies.
Evaporation, transpiration and evapotranspirationStudent
1) Evaporation, transpiration, and evapotranspiration are key processes in the hydrological cycle. Evaporation is the process by which liquid water changes to a gas, transpiration is the process by which plants release water vapor into the air, and evapotranspiration accounts for both soil evaporation and plant transpiration.
2) There are several methods for measuring evapotranspiration rates, including lysimeters, water balance methods, eddy covariance, and remote sensing techniques using satellites.
3) Potential evapotranspiration refers to the theoretical maximum amount of water that could be evaporated or transpired, while actual or effective evapotranspiration depends on available water supply from the soil and
This document discusses the importance of drainage in irrigated agricultural areas. It defines drainage as the removal of excess water from soil. Excess water can come from heavy rainfall or over-irrigation and can cause waterlogging of soils. Waterlogging deprives plant roots of oxygen and can lead to increased soil salinity. The document outlines various causes and effects of waterlogging and describes different types of drainage systems including surface drainage, subsurface drainage, vertical drainage, well drainage, controlled drainage, bio-drainage and their characteristics and advantages. Research on the impact of subsurface drainage in reclaiming waterlogged salt-affected soils in Andhra Pradesh, India is summarized which shows that drainage reduces soil salinity and increases crop yields.
This document discusses the quality of irrigation water and criteria for determining water quality. It outlines 5 classes of water salinity based on electrical conductivity and 4 classes of sodium level based on sodium adsorption ratio. It also discusses acceptable boron levels and provides management practices for using poor quality water, including applying gypsum, alternate irrigation strategies, fertilizer application techniques, irrigation methods, growing crop varieties, drainage, and other soil management practices. The document concludes with a discussion of soil fertility versus productivity and different methods for evaluating soil fertility.
Irrigation engineering involves planning and designing water supply systems for crop irrigation. Key factors that necessitate irrigation include insufficient or uneven rainfall, requirements of perennial crops, and converting desert areas. Benefits of irrigation include increased crop yields, elimination of mixed cropping, prosperity of farmers, and sources of revenue from water taxes. Factors affecting the water requirements of crops include climate, soil type, irrigation method, and ground slope. Important terms include gross command area, culturable command area, crop rotation, base period, delta, and duty. The relationship between duty, base period, and delta is defined. Methods to improve duty involve efficient irrigation methods, reducing canal seepage and evaporation losses, and farmer training.
This document discusses the scheduling of irrigation for crop production. It explains that irrigation needs to supply water to crops as required at different growth stages, as rainfall and groundwater are often inconsistent with crop needs. Certain periods are critical for water requirements for each crop. Irrigation should be scheduled around these critical stages if no other water source is available. The document provides examples of critical stages for various crops and discusses factors to consider for irrigation quantity, interval, and total number based on soil, crop type, and cultural practices.
The document discusses the relationship between soil, water, and plants. It covers several key topics:
- The importance of water for plant growth and physiological processes like germination, photosynthesis, and transpiration. Water is necessary for these processes and makes up a large percentage of fresh plant tissues.
- The movement and storage of water in soil, including gravitational, field capacity, and hygroscopic water. Plants can only access water within a certain soil water potential range.
- The mechanisms by which plants absorb water from soil, including passive absorption via transpirational pull and active absorption using energy. Absorption is influenced by root properties and environmental factors.
- How nutrients move from soil to plant
This document discusses various methods for irrigation scheduling to maximize crop yields. It defines irrigation scheduling as determining the frequency and timing of water applications based on crop needs and soil conditions. Direct approaches determine optimal schedules through field trials of different watering intervals and depths, while indirect approaches use indicators like soil moisture levels or sensitive plant species to determine crop water needs. More accurate mathematical approaches estimate needs based on climate data, soil type, and crop water requirements. The document also discusses practical considerations like soil properties, irrigation methods, and minimizing excess water that can damage crops. Overall, the goal of irrigation scheduling is to meet crop water demands and maximize production using water resources efficiently.
Proper irrigation scheduling determines when and how much to irrigate crops. It is important for efficient water use and maximizing yields. Methods for determining when to irrigate include soil moisture indicators like tensiometers, plant indicators like wilting, and meteorological data. The amount of irrigation applied should bring the soil moisture in the effective root zone to field capacity, accounting for expected rainfall and crop water needs.
Soil, plant and meteorological factors determining water needs of cropsKhileshKumarsahu
Khilesh Kumar Sahu presented on factors determining water needs of crops. Evapotranspiration is the combined water loss from soil and plant surfaces through evaporation and transpiration. It is influenced by climatic factors like temperature, humidity, solar radiation and wind speed. Crop characteristics like crop type, leaf area, and root depth also impact water needs. Properly understanding evapotranspiration allows farmers to effectively schedule irrigation and maximize crop water utilization.
The document discusses measures to increase water use efficiency in Indian agriculture. It notes that agriculture accounts for 80-84% of water consumption in India but has low productivity and efficiency. Key challenges include limited technical capabilities, lack of capital, and inability to recover costs. Methods to improve efficiency include improving storage systems, conveyance infrastructure, and on-farm irrigation techniques. These involve reducing evaporation, seepage, waterlogging, and employing micro-irrigation, treated wastewater reuse, and growing less water-intensive crops. The document anticipates irrigation efficiency could increase to 50-60% for surface water and 72-75% for groundwater by 2025-2050 through these measures.
Irrigation methods are classified into four main types: surface irrigation, subsurface irrigation, sprinkler irrigation, and drip irrigation. Surface irrigation includes gravity-fed methods like flood, basin, border, and furrow irrigation. Water is applied to the soil surface and distributed by gravity. Subsurface irrigation involves applying water below the soil surface using trenches or perforated pipes. Sprinkler irrigation simulates natural rainfall by spraying water into the air through nozzles above the crop. Drip irrigation applies water slowly to the soil surface near plants through a network of valves, pipes, tubing, and emitters.
Irrigation is the process of transporting water from areas with abundant supply like rivers or reservoirs to drier areas for agricultural and domestic purposes. Ancient Mesopotamians and Egyptians developed early irrigation systems using dams, reservoirs, and canals to supply water to lands away from water sources. Irrigation was invented to allow people living farther from water access to drink, grow crops, and meet other needs, and made obtaining water more reliable and regular. Today, irrigation continues to enable farming in more places and help ensure a secure food supply for more people.
1. Irrigation is the artificial supply of water to crops through methods like surface, sprinkler, and drip irrigation. Surface irrigation involves distributing water over the soil surface by gravity in techniques like basin, border, and furrow irrigation.
2. Sprinkler irrigation applies water similar to rainfall through pipes and sprinklers. Drip irrigation drips water slowly from pipes and emitters directly to plant roots.
3. The suitable irrigation method depends on factors like soil type, crop type, technology, costs and previous experience. Surface irrigation is common on loamy and clay soils while sprinkler and drip are more suitable for sandy soils with low water storage.
Introduction:
Necessity of irrigation- scope of irrigation engineering- benefits and ill effects of irrigation- irrigation development in India- types of irrigation systems, Soil-water plant relationship: Classification of soil water- soil
moisture contents- depth of soil water available to plants-permanent
and ultimate wilting point
Water requirements of crops:
Depth of water applied during irrigation- Duty of water and deltaimprovement
of duty- command area and intensity of irrigation consumptive use of water and evapotranspiration- irrigation efficiencies- assessment of irrigation water
This document summarizes four main irrigation methods: surface irrigation (flooding), sprinkler irrigation (applying water under pressure), drip or trickle irrigation (applying water slowly to the soil), and sub-surface irrigation (flooding water underground). Surface irrigation is the most widely used method, covering 90% of irrigated land. Sprinkler irrigation is ideal for scarce water areas. Drip irrigation conserves water, controls weeds, and applies water at a slow rate matching crop needs. Sub-surface irrigation is used where soil and topography allow watering underground.
The document provides an outline and summary of a presentation on irrigation. It begins with definitions of irrigation and its uses in crop production. It then discusses the history of irrigation in ancient civilizations like Peru and India. Current global statistics on irrigation are presented, showing that 68% of irrigated land is in Asia. The main types of irrigation systems - surface, center pivot, lateral move, and localized drip/sprinkler - are described. Issues with irrigation in Bangladesh like groundwater depletion and arsenic contamination are raised. The presentation advocates for more efficient irrigation methods like bucket drip kits to minimize water waste.
This document summarizes a study on the effect of deficit irrigation on soil properties, physiology, and nutrient assimilation of sweet pepper. The study used three irrigation treatments (100%, 90%, and 80% of crop water requirement) in a randomized block design. Data was collected on soil physical and chemical properties, dry matter accumulation, harvest index, and nutrient uptake. The results of the study will help optimize irrigation for sweet pepper crops during times of drought or water abundance.
Dams , piping, uplift Pressure, Khosla’s Theory, causes of Failure of Hydraulic structure by piping and uplift pressure
what is the importance of reservoir planning and dams? Discuss multipurpose reservoir in detailed, Give Economic height of dam.
A REVIEW OF VARIOUS SOIL MOISTUREMEASUREMENT TECHNIQUESBhushan Patil
This paper presents review of the different eight methods for measurement of soil moisture and describes the principle used, methodology, advantages, disadvantages and comparison. Described methods are Gravimetric method, Neutron moderation (NM), Time Domain Reflectometer (TDR), Frequency Domain Reflectometer (FDR), Amplitude Domain Reflectometer (ADR), Phase Transmission (PT), Time Domain Transmission (TDT) and Tensiometer method.
R 12013(ssc-411)-soil moisture constants,soil-water movement & infiltrationKritika Somya
This document discusses soil water and defines key terms related to soil moisture content and movement. It defines classifications of soil water, soil moisture constants like field capacity and wilting point, saturated and unsaturated water flow, infiltration, and factors that influence soil water movement. Diagrams show the relationship between soil moisture tension and water content. Soil water is essential for plant growth and understanding these concepts helps determine moisture levels in soil.
An irrigation system consists of several key components including emitters, PVC pipes and fittings, control units, valves, and sensors. Emitters deliver water to plants and come in different types. PVC pipes and fittings connect all parts of the system and carry water. Control units program watering schedules. Valves control water flow. Sensors detect conditions to optimize watering. Drip irrigation is an effective water-saving method using these components. Larger commercial systems also include pumps, filters, monitoring equipment and large diameter pipes to irrigate over larger areas.
This document discusses methods for estimating soil moisture content. It defines soil moisture as the water held in the spaces between soil particles, particularly in the top 200 cm that is available to plants. There are direct methods that measure the moisture content through gravimetric techniques like oven drying samples, and volumetric methods using bulk density. Indirect methods measure water potential or tension, including tensiometers, gypsum blocks, and neutron probes. Remote sensing techniques estimate soil moisture from visible/infrared reflectance, thermal infrared surface temperature, and passive/active microwave emissions and backscattering related to dielectric properties.
Chapter 3 soil water and irrigation practice1Mulugeta Abera
This document summarizes key concepts about soil water and irrigation practices. It discusses how soil serves as a storehouse for water and nutrients that are essential for plant growth. The document then describes the three-phase system of soil consisting of solids, liquids, and gases. It explains how soil texture, structure, and physical properties influence the soil's water holding capacity and retention. Different types of soils like sandy soil, loamy soil, and clay soil are characterized. The concept of bulk density, porosity, and soil moisture content on a mass and volume basis are introduced to quantify the water in soil. Maintaining proper soil water levels through irrigation is important for optimal plant growth and yield.
this section speaks about the quantity flow meter and its different types i.e. positive displacement flow meter and metering pump, it comprises discussion on mass flow meter, coriolis flow meter, variable reluctance tacho generator and linear resistance element flow meter.
This document provides an overview of irrigation engineering. It discusses the necessity of irrigation, benefits and ill-effects. It covers types of irrigation systems, soil-water relationships, irrigation development in India, and key concepts like duty and delta. Engineering, agriculture, and management aspects are described. Factors affecting evapotranspiration and methods to measure it are also summarized.
There are two main types of spillways: controlled and uncontrolled. Controlled spillways have gates to regulate water flow, while uncontrolled spillways release water once it reaches the spillway crest without gates. Spillways are further classified by their shape, including straight drop, side channel, ogee, labyrinth, chute, conduit/tunnel, and baffled chute spillways. Each type has distinct characteristics regarding how it structures and releases water from a reservoir.
This document discusses sprinkler irrigation and includes the following key points:
1. A group of 6 students will present on the topic of sprinkler irrigation. Sprinkler irrigation can save up to 50% of water compared to surface irrigation.
2. Sprinkler irrigation works by using pressurized sprinklers located on pipes to discharge water into the air so it infiltrates near where it lands.
3. The components of a sprinkler system include a water source, pumping unit, pipes, sprinklers, and accessories like reducers, elbows, valves, and filters. Proper design considerations include layout, pressure, and matching the system to soil and crop types.
Speaks about the different aspects of flow measurement i.e. flow types, fluid types, its units, selection parameters; definition of common terms, coanda effect coriolis effect . it also speaks about the factors affecting flow measurement.
This document discusses and defines different types of spillways used in dams. It describes controlled and uncontrolled spillways. Controlled spillways have gates to regulate water flow, while uncontrolled spillways release water once it reaches the spillway crest. The document then outlines and provides diagrams for several types of spillways including: straight drop, overflow, chute, side channel, shaft, siphon, labyrinth, and cascade spillways. Each type has distinct structural features and purposes in safely releasing water from reservoirs.
it speaks about the differential head flow meters. its different types. their principle of operation, venturi meter, orifice plate, rotameters, it also covers discussion on open channel flow meter. it covers the different application domains of the different types of flow meters and their advantages and disadvantages.
Topics:
1, Introduction to Irrigation
2. Methods of Irrigation
3. Indian Agricultural Soils
4. Methods of Improving Soil Fertility & Crop Rotation
5. Soil-Water-Plant Relationship
6. Duty and Delta
7. Depth and Frequency of Irrigation
8. Irrigation Efficiency and Water Logging
This document discusses irrigation water management. It notes that declining groundwater levels and restrictions on new irrigated acres mean irrigators need to schedule irrigation applications carefully. Proper irrigation scheduling involves routinely measuring soil water status, rainfall, irrigation applied, and estimating crop water use. The goal is to irrigate with appropriate amounts and frequencies to match crop needs. Over-irrigation can reduce yields, increase costs, and contribute to groundwater contamination. Key factors for proper irrigation management include having an irrigation system designed for efficient water delivery, flow meters, rain gauges, soil moisture sensors, and reliable crop water use information.
The document discusses soil constituents and their proportions, including minerals, organic matter, water, and air. It describes the mineral components of soil in detail, including primary and secondary minerals. It also explains concepts such as soil water potential, classes of soil water, field capacity, permanent wilting point, and available moisture. The water requirements of crops are defined as the total quantity and timing of water needed from sowing to harvest, which can vary by crop and location. Irrigation may be necessary where rainfall is insufficient or unreliable to meet crop water needs.
Water is essential for plant growth and agriculture relies heavily on irrigation. The document discusses water management in horticulture, including the importance and functions of water in plants. It also covers the history of irrigation in India, different irrigation methods, the impact of moisture stress on crops, and strategies for scientific irrigation management. Key crops irrigated in India are also listed.
Water use effeciency intrinsic water use effeciency as a drought resistant traitZuby Gohar Ansari
This document discusses water use efficiency (WUE), an important trait for developing drought-resistant crops. It defines WUE as the amount of dry matter or yield produced per unit of water used. Higher WUE is significant for crop productivity under water-limited conditions. WUE is influenced by both environmental factors like vapor pressure deficit, light, temperature, and CO2 concentration as well as plant factors like root systems, leaf movements, and nutrient availability. Improving WUE through breeding and management techniques like irrigation method, mulching, and weed control can help increase crop yields in drought conditions.
This document provides an overview of fundamental concepts in irrigation, including definitions of key terms, factors that influence irrigation efficiency, different irrigation methods, and crop water requirements. It defines irrigation as the artificial application of water to supply moisture for plant growth. Surface irrigation, sprinkler irrigation, and drip irrigation are described as the main methods. Critical growth stages and how crop water needs vary throughout growth are also covered.
I have tried to discuss about the fundamental knowledge related to Irrigation and Flood Control in short. For more details anyone can visit the books that I have mentioned in my slide presentation. I have tried to cover major topics from books so that student can find it easy to understand and learn about irrigation and flood control. I hope it will help everyone who has interest to Irrigation Engineering.
The document discusses factors that influence crop water needs, including climate, crop type, and growth stage. It defines crop water need (evapotranspiration) as the amount of water needed to meet water loss through transpiration and evaporation from the soil and plant. Crop water need depends mainly on climate (hotter/drier climates require more water), crop type (some crops like rice and sugarcane need more than others), and growth stage (fully grown crops need more than newly planted crops). Standard reference values are provided for determining crop water needs in different climates and for various crop types.
This document discusses various topics related to irrigation including:
1. The necessity of irrigation due to factors like low and uneven rainfall as well as growing multiple crops per year.
2. The advantages of irrigation such as fulfilling crop water requirements, improving yields and living standards, adding to national wealth and revenue, and enabling cash crops.
3. Key terms related to irrigation water requirements including consumptive use, net irrigation requirement, and gross irrigation requirement.
4. Factors that affect the duty of water applied such as irrigation methods, crop type, climate, canal conditions, water quality, soil characteristics, topography, and cultivation methods.
The document discusses soil-water-plant relationships, including:
1) The soil-plant-atmosphere continuum (SPAC) which defines the movement of water from soil through plants to the atmosphere.
2) Soil water holding capacity is determined by soil texture, porosity, and the forces that hold water in place.
3) Effective irrigation requires understanding concepts like evapotranspiration, effective rainfall, irrigation requirements, and management-allowed deficit which indicates how much available soil water can be depleted before irrigating.
Alternate wetting and drying (AWD) is an irrigation practice for rice that saves water and reduces greenhouse gas emissions while maintaining yields. It involves periodically drying and re-flooding rice fields. In Bangladesh, boro rice is fully irrigated while aman rice is partly irrigated. Research shows AWD can save 15-30% of the estimated 3,000-5,000 liters of water needed to produce one kilogram of rice, without lowering yields. The practice involves irrigating until the water table is 20cm below ground, then allowing the field to partially dry before re-flooding. This technique is being validated in Bangladesh and could help conserve irrigation water and reduce environmental impacts.
The document provides information about a seminar on water management in agriculture given by Garima Bhickta. It discusses various topics related to water management including terminology, water requirements of crops, irrigation scheduling tools and methods, rainwater harvesting, and drip irrigation. Specifically, it summarizes different methods of irrigation like surface, sprinkler and drip irrigation. It also provides data on increased yields from various crops with drip irrigation compared to conventional irrigation methods and higher water use efficiency.
The loss of water from aerial parts of plants in the form of vapor is known as transpiration.
The loose arrangement of the living thin walled mesophyll cells, which results in an abundance of inter cellular space provides an ideal condition for the vaporation of water from internal leaf surface.
Part of the epidermal surface of the leaf is made up of a great number of microscopic pores called stomata.
Evapotranspiration-ET- definition and measurementpavik13
Evapotranspiration is the combined process of evaporation from soil and plant surfaces and transpiration from plants. It accounts for the movement of water from the soil, through plants, and into the atmosphere. Key factors that influence evapotranspiration are solar radiation, temperature, humidity, wind, soil moisture, and plant characteristics. Evapotranspiration can be estimated using lysimeters, which directly measure water loss, or models based on climatic data like the Penman-Monteith equation. It is an important consideration in agricultural water management.
Soil, Plant, water and atmosphere relationshipgtc21187
1. Soil and water are vital resources for plant growth. Soil provides nutrients and support for roots while water transports nutrients and helps plants grow.
2. The water retention properties of soil like bulk density and particle size determine how much water the soil can hold. Generally, finer textured soils like clay retain more water than coarser soils like sand.
3. The soil-water retention curve shows the relationship between soil water content and pressure head. It allows determining how much water the soil holds at different tensions.
This document discusses various techniques for soil moisture conservation. It explains that soil moisture conservation aims to minimize water loss from soil through evaporation and transpiration. It then discusses different agronomic measures like conservation tillage, deep tillage, contour farming, mulching, crop rotation, and use of cover crops and anti-transpirants to conserve soil moisture. The document also discusses mechanical measures like bunding, terracing, trenching etc. that are used for soil moisture conservation, especially on lands with slopes greater than 2%.
This document discusses dryland agriculture, which refers to growing crops entirely through rainfall. It can be divided into dry farming (<750mm rainfall), dryland farming (750-1150mm rainfall), and rainfed farming (>1150mm rainfall). Dry farming occurs in arid regions and has frequent crop failures due to low and variable rainfall. Dryland farming occurs in semi-arid regions and has less frequent crop failures. Rainfed farming occurs in humid regions and has rare crop failures. The document also discusses various irrigation techniques like surface, localized, and subsurface irrigation that help supplement rainfall for crop growth.
Rice requires ample water to grow and is usually cultivated with continuous flooding or intermittent flooding of rice fields. The total water requirement for rice is approximately 1,100-1,250 mm, with the critical growth stages being active tillering, panicle initiation, booting, heading, and flowering when water stress can severely impact yields. Proper water management through irrigation practices such as intermittent flooding, shallow and controlled flooding, and reducing percolation losses through soil management are important for optimizing rice production.
Rice requires ample water to grow and is most widely cultivated in areas with high rainfall or irrigation. The average total water requirement for rice is 1100-1250 mm, with the critical stages being active tillering, panicle initiation, booting, heading, and flowering when water stress can severely impact yields. Water can be managed through continuous shallow submergence, intermittent submergence during critical stages, or saturation without submergence to reduce water needs while maintaining high yields.
Similar to Principles of irrigation by Dr Thomas Abraham_Course Code_Chapters 1 to 5__26-3-2014 (20)
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Callum Wright - Founder and Lead Consultant Founder and Lead Consultant
Callum Wright is a seasoned cybersecurity, privacy and AI governance expert. With over a decade of experience, he has dedicated his career to protecting digital assets, ensuring data privacy, and establishing ethical AI governance frameworks. His diverse background includes significant roles in security architecture, AI governance, risk consulting, and privacy management across various industries, thorough testing, and successful implementation, he has consistently delivered exceptional results.
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Date: June 26, 2024
Tags: ISO/IEC 42001, Artificial Intelligence, EU AI Act, ISO/IEC 23894
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Principles of irrigation by Dr Thomas Abraham_Course Code_Chapters 1 to 5__26-3-2014
2. Irrigation can be defined as the artificial application of water
to the crop root zone to meet its consumptive use which can
not be provided by rainfall.
Therefore, need for irrigation is as follows :
Where, Rainfall is not sufficient to supply crop water
needs
Where rainfall is not uniformly distributed to supplement
the crop requirement
If there is variable crop water requirement
1. Introduction
3. Irrigation maximizes crop productivity and thereby
ensures food security
It makes agricultural industry profitable and competitive
Irrigation improves land productivity and value of land
Promotes employment generation and lively hood of society
Main conveyance/irrigation canals can be used for flood
protection, recreation and navigation.
It promotes fish and wildlife preservation
Rapid development of irrigation facilities through construction
of multipurpose dams enhances hydroelectric power
generation.
Irrigation promotes a whole array of agro-based industries
which are drive engines of economy.
Direct/indirect benefits of Irrigation
4. 1. Irrigation supplies moisture to the soil essential for,
germination of seeds and various growth processes of
crop.
2. Cools the soil and the surroundings thus making the
environment more favorable for crop growth.
3. Washes out or dilutes salts present in the soil.
4. Softens the clods and thus helps in tillage operations.
5. Enables application of fertilizers.
6. Reduces the adverse effects of frost on crops.
7. Ensures crop success against short duration drought.
Functions of Irrigation
5. Stabilized Yield of Crops
Protection from Famine
Improvement of Cash Crops
Prosperity of Farmers
Source of revenue
Navigation
Hydroelectric Power Generation.
Water Supply
General Communication
Development of Fishery
Advantages of Irrigation
6. At the micro level:
Irrigation leads to an increase in yield per hectare
Subsequent increases in income, consumption and
food security.
Irrigation enables smallholders to diversify cropping
patterns
To switch from low- value market subsistence
production to high-value market –oriented production.
Contribution of Irrigation to Country’s Economy
7. Irrigation benefits through :
higher production, higher yields, lower risks of crop failure,
and higher and all year round farm as well as non-farm
employment.
In Ethiopia during dry season, farmers grow Cereals and a
variety of Vegetables including Onions, Tomatoes, and
Leafy Green Vegetables like Lettuce under full irrigation.
Farmers also grow perennial crops like Mango, Banana,
Chat, Sugarcane etc. which are sometimes intercropped
with seasonal crops
Benefits of Irrigation in Ethiopian Scenario
8. Therefore, we can summarize the
To ensure enough moisture essential for plant life.
To provide crop insurance against short duration
drought.
To cool the soil and atmosphere to provide a
favorable environment for plant growth.
To wash out or dilute harmful salts in the soil
To soften the tillage pans.
Objectives of irrigation
9. Full Irrigation :
Under adequate water supply (i.e., full irrigation), the crop
water requirement is fully met.
Crop water consumption (ETa) in this case is equal to the
maximum evapotranspiration (ETm),
i.e., ETa = ETm.
No water stress develops under such conditions, and crop
yield (Ya) is expected to be potential yield (Ym), i.e.
Ya = Ym (if other production factors are not limiting).
1.2. Types of Irrigation
10. Under limited water supply (i.e., water stress or water
deficit) :
- the level of soil water status within the plant root zone is
less than what would be under full irrigation.
Crop water consumption in this case (ETa) falls below
maximum evapotranspiration (ETm), i.e. ETa < ETm.
Under such conditions, water stress will develop in the
plant, which will adversely affect crop growth, and
therefore the expected yield (i.e., actual yield, Ya) will be
less than the potential yield, i.e. Ya < Ym.
Deficit Irrigation
11. Supplemental irrigation (SI) can be defined as the
addition of small amounts of water to essentially rainfed
crops during times when rainfall fails to provide sufficient
moisture for normal plant growth, in order to improve and
stabilize yields. SI in areas with limited water resources is
based on the following three grounds:
Water is applied to a rainfed crop which would normally
produce some yield without irrigation.
SI is only applied when precipitation fails to provide
essential moisture for improved and stabilized production.
Supplemental Irrigation
12. The amount and timing of SI are not scheduled to provide
moisture-stress-free conditions throughout the growing
season, but to ensure that the minimum amount of water
required for optimal (not maximum) yield is available
during the critical stages of crop growth.
Supplemental irrigation is the opposite of full or
conventional irrigation (FI). SI is dependent on the
precipitation of a basic source of water for the crop.
Supplemental Irrigation (cont..)
13. Soil can be regarded as a porous medium, consisting of ;
Solid,
Liquid and
Gaseous phases.
Solid phase comprises :
Mineral material,
Organic Matter (OM) and
living Micro Organisms which decomposes various
residues into beneficial Humus.
Organic Matter content in a mineral soil is usually
between 1 and 4% by dry weight.
Soil and Its Constituents
14. Organic soil is clay soil with more than 30% OM or a
sandy soil with more than 20% OM.
If a soil contains more than 65% OM it is called a peat
soil.
Mineral and organic compounds of the soil form the soil
matrix or 'skeleton' of the soil.
Part of the soil not occupied by the matrix is the pore
space or voids.
For most agricultural crops the ideal soil consists of
approximately 50% solid material and 50% pores, half of
which are filled with water.
Soil and Its Constituents (cont..)
15. Many of the physical and chemical properties of soil
are affected by soil texture.
Soil texture is described by classifications which are
determined by the particle size, distribution of sand,
silt, and clay within the soil.
Particle size distribution of soil can be measured in
the laboratory.
After pretreatment of the soil sample, the sand
fractions are measured using mesh sieves of various-
sized openings.
Soil texture
Soil PropertiesSoil Properties
16. Soil Texture
Definition: relative proportions of various sizes of
individual soil particles
USDA classifications
Sand: 0.05 – 2.0 mm
Silt: 0.002 - 0.05 mm
Clay: <0.002 mm
Textural triangle: USDA Textural Classes (previous slide)
Affects water movement and storage
Soil Structure
Definition: how soil particles are grouped or arranged
Affects root penetration and water intake and
movement
Soil PropertiesSoil Properties (cont…)(cont…)
19. Bulk density is the ratio of the mass of solids to the
total soil volume.
It can be used to estimate the degree of compaction
It is needed to calculate soil moisture content and
porosity.
Bulk density of soil is influenced by soil structure due
to its looseness or degree of compaction and by its
swelling and shrinking characteristics.
Bulk density of Soil
20. Bulk Density (ρb)
◦ ρb = soil bulk density, g/cm3
◦ Ms = mass of dry soil, g
◦ Vb = volume of soil sample, cm3
Typical values: 1.1 - 1.6 g/cm3
Particle Density (ρp)
◦ ρP = soil particle density, g/cm3
◦ Ms = mass of dry soil, g
◦ Vs = volume of solids, cm3
Typical values: 2.6 - 2.7 g/cm3
b
s
b
V
M
=ρ
s
s
p
V
M
=ρ
Bulk density of Soil
21. Pore spaces in the soil matrix vary in amount, size,
shape, and continuity.
Porosity is an important physical property of the soil,
especially with regard to the retention of soil water.
Porosity is important because it is a measure of the
soil’s capacity to infiltrate water.
Porosity is the volume fraction of pores and ranges
from 0.3 to 0.6 for most soils.
Porosity is equal to the pore volume divided by the
original soil volume.
Porosity
24. Development of sustainable irrigation practices will
require that we understand better the biophysical
processes of root-water uptake in soil, and transpiration to
plant canopies.
Solar energy is the driving force for most of the
biophysical processes in the plant system and water
movement from soil to the atmosphere.
25. A plant grows in soil and opens to atmosphere. About
99% of all the water that enters the roots leaves the plant’s
leaves via the stomata without taking part in metabolism.
On a dry, warm, sunny day, a leaf can evaporate 100% of
its water weight in just an hour. Water loss from the
leaves must be compensated for by the uptake of water
from the soil.
Water movement is due to differences in potential
between soil, root, stem, leaf, and atmosphere
26. Under normal conditions, the water potential in soil is
higher than that in root saps or fluids.
- (Negative potential)
Typical moist soil might have a water potential of about
0.3 to 1.0 Bar,
- root tissue about 4.0 Bar, stem about 7.0 Bar,
- leaf about 10.0 to 12.0 Bar,
- dry atmosphere about 400 to 600 Bar.
These differences in water potential (and hence potential
gradient) are the driving force for causing water
movement.
Water Potential
Chapter - 3
27. Water potential of the atmosphere is computed as:
Water Potential of
Atmosphere
29. Soil water content
Mass water content (θm)
θm = mass water content (fraction)
Mw = mass of water evaporated, g
(≥24 hours @ 105o
C)
Ms = mass of dry soil, g
s
w
m
M
M
=θ
Water in SoilsWater in Soils
30. θV = volumetric water content (fraction)
Vw = volume of water
Vb = volume of soil sample
θV = As θm
As = apparent soil specific gravity = ρb/ρw
(ρw = density of water = 1 g/cm3
)
As = ρb numerically when units of g/cm3
are used
Equivalent depth of water (d)
d = volume of water per unit land area =
(θv A L) / A = θv L
d = equivalent depth of water in a soil layer
L = depth (thickness) of the soil layer
b
w
v
V
V
=θ
Volumetric water content (θv)
32. 1 in.1 in.
0.50 in.0.50 in.
0.15 in.0.15 in.
0.20 in.0.20 in.
0.15 in.0.15 in.
Soil Solids (Particles): 50%Soil Solids (Particles): 50%
Total PoreTotal Pore
Space: 50%Space: 50%
Very Large Pores: 15%Very Large Pores: 15%
(Gravitational Water)(Gravitational Water)
Medium-sized Pores: 20%Medium-sized Pores: 20%
(Plant Available Water)(Plant Available Water)
Very Small Pores: 15%Very Small Pores: 15%
(Unavailable Water)(Unavailable Water)
Volumetric Water Content &Volumetric Water Content &
Equivalent DepthEquivalent Depth :: Typical Values for Agricultural SoilsTypical Values for Agricultural Soils
33. Coarse SandCoarse Sand Silty Clay LoamSilty Clay Loam
Gravitational WaterGravitational Water
Water Holding CapacityWater Holding Capacity
Available WaterAvailable Water
Unavailable WaterUnavailable Water
Dry SoilDry Soil
Water-Holding Capacity of Soil :Water-Holding Capacity of Soil :
Effect of Soil TextureEffect of Soil Texture
34. • Soil-water content refers to the amount of water present in
the soil. The soil-water content can be expressed in two
ways:
• on the basis of its quantity
• on the basis of its energy or potential
• 2.2. Forces acting on soil-water
• Several forces at the molecular level interact :
• Molecular-level cohesive and adhesive forces-
• Cohesion – attraction between like molecules
• Adhesion – attraction between differing molecules
• - hold water between soil particles and on the surfaces of
soil particles.
• Cohesive forces hold capillary water and adhesive forces
hold the hygroscopic water.
Soil-water content
36. Water molecules
(+ve charged) is
attracted to the
negatively
charged surfaces
of soil solids
(adheision force)
Negatively
charged soil
solid
surfaces
Figure: Adsorbed (hygroscopic) water
adheres so tightly to soil particles that it can
be removed only by oven-drying the
soil. It is not available to plants.
37. Adsorbed water
Capillary water
Adhesion results from double-layer forces.
Adsorbed (hygroscopic) water adheres so tightly to soil
particles; it can be removed only by oven-drying the soil.
Capillary water coheres to adsorbed water and to itself. (Cohesion force)
•Gravitational force – acts on soil-water in the macro pores under saturated
conditions and tends to move water downward.
•Osmotic forces – are very important in saline soils and move water across
plant membranes.
38. Some points about potential concept :
• The concept of energy is the most important concept
in nature.
• This is because energy is a fundamental entity
common to all forms of matter.
• Water retention in the soil is a consequence of energy
effects.
• Capacity of doing work is called energy.
• The concept of energy is, therefore, closely linked to
the concept of work.
39. • Depending on how work is done, two kinds of mechanical
energy are distinguished:
• Potential energy – if by virtue of its position or state a body
is able to do work.
• Kinetic energy- if a body is able to do work by virtue of its
motion.
• Since the movement of water in the soil is very slow, the
contribution of kinetic energy to flow of water in soil is
negligible compared to that of potential energy.
• In the soil system, the state and movement of water is
determined by its potential energy.
• The amount of work done, or potential energy stored, per
unit mass in bringing any mass, m, from the reference to the
point in question is called potential.
40. • Expression in terms of energy makes it more easy to
compare availability of the moisture in soils of
different textures.
• Most commonly accepted unit at present is bars of
suction.
• Suction is negative pressure, the higher the numerical
value - the lower the energy status of the water.
• Soils at field capacity - 0.1 - 0.3 bars of suction
• When soils at wilting point - 15 bars of suction
• CONCEPT Managing soil moisture is the critical
management component of irrigated agriculture.
41. • Water will move in a soil from one point to
another if the water at the first point has higher
energy status than the water at the second.
• The rapidity of movement depends on the size of
the energy difference and soil characteristics.
• If water is applied to the surface by rain or
irrigation is much faster than it can enter soil and
be transmitted downward, the excess water
accumulates on the surface.
• If the slope is great, erosion will likely result
(unless surface stable or protected by plant
residues).
42. Measure of the energy status of the soil water
Important because it reflects how hard plants must
work to extract water
Units of measure are normally bars or atmospheres
Soil water potentials are negative pressures (tension
or suction)
Water flows from a higher (less negative) potential
to a lower (more negative) potential
43. • Gravity is the dominant force acting on soil
water when soils are wet.
• Water tends to flow downward- from a region
of more positive potential to one of less
positive potential- under the influence of
gravity, until the force of gravity is balanced
by that of capillarity.
44. • Matric potential is due to the attraction of soil
surfaces for water as well as to the influence
of soil pores.
• Matric potential is, therefore, the result of
two phenomena
• Adsorption
• Capillarity
• The soil solids tightly adsorb water, whereas
capillary forces are responsible for the water
being held in the capillary pores.
45. • The osmotic potential is attributable to the
presence of solutes in the soil.
• It results from dissolved solutes lowering the
free energy of soil-water and is always
negative.
46. Components :Components :
◦ ψt = total soil water potential
◦ ψg = gravitational potential
◦ ψm = matric potential
◦ ψo = osmotic potential
◦ Matric potential, ψm, normally has the greatest
effect on release of water from soil to plants
omgt ψψψψ ++=
47. Curve of matric potential (tension) vs. water content
Less water → more tension
At a given tension, finer-textured soils retain more water
(larger number of small pores)
Soil Water Release Curve
48. Height of capillary
rise inversely related
to tube diameter
Tension or suction created by small capillary tubes
(small soil pores) is greater that that created by large
tubes (large soil pores).
At any given matric potential coarse soils hold less
water than fine-textured soils..
Matric Potential and Soil Texture
Small soil pores
Large soil pores
49. –Soil water content where gravity drainage becomes
negligible
–Soil is not saturated but still a very wet condition
–Defined as the water content corresponding to a soil water
potential of -1/10 to -1/3 bar
–Soil water content beyond which plants cannot recover
from water stress (dead)
– (Plants can no longer absorb water)
–Still some water in the soil but not enough to be of use to
plants
–Traditionally defined as the water content corresponding
to -15 bars of suction
Field Capacity (FC or θθfcfc)
Permanent Wilting Point (WP or
θθwpwp)
50. Definition :
Water held in the soil between field capacity and
permanent wilting point
“Available” for plant use
Available Water Capacity (AWC)
AWC = θfc - θwp
Units: depth of available water per unit depth of
soil (in/in, or mm/mm)
Measured using field or laboratory methods
Available WaterAvailable Water
51. (θfc - θv) = Soil Water Deficit (SWD)
θv = current soil volumetric water content
Fraction available water remaining (fr)
(θv - θwp) = soil water balance (SWB)
=
wpfc
vfc
df
θθ
θθ
=
wpfc
wpv
rf
θθ
θθ
Fraction available water depleted (fd)
52. TAW = (AWC) (Rd)
TAW = total available water capacity within the
plant root zone(mm).
AWC = available water capacity of the soil,
(mm of H2O/mm of soil)
Rd = depth of the plant root zone, (mm)
If different soil layers have different AWC’s, need
to sum up the layer-by-layer TAW’s
TAW = (AWC1) (L1) + (AWC2) (L2) + . . . (AWCN) (LN)
- L = thickness of soil layer, (mm)
- 1,2,N: subscripts represent each successive soil layer
Total Available Water (TAW)
53. Horizontal movementHorizontal movement
due to capillaritydue to capillarityVertical movementVertical movement
due largely to gravitydue largely to gravity
Gravity vs. CapillarityGravity vs. Capillarity
54. Influencing FactorsInfluencing Factors
Soil texture
Initial soil water content
Surface sealing (structure, etc.)
Soil cracking
Tillage practices
Method of application (e.g., Basin vs. Furrow)
Water temperature
Water Infiltration -Water Infiltration -
Entry of water into the soilEntry of water into the soil
57. Gravimetric
Measures mass water content (θm)
Take field samples → weigh → oven dry → weigh
Advantages: accurate; Multiple locations
Disadvantages: labor; Time delay
Feel and appearance
Take field samples and feel them by hand
Advantages: low cost; Multiple locations
Disadvantages: experience required; Not highly accurate
Soil Water MeasurementSoil Water Measurement
58. Neutron scattering (attenuation)
Measures volumetric water content (θv)
Attenuation of high-energy neutrons by hydrogen nucleus
Advantages:
samples a relatively large soil sphere
repeatedly sample same site and several depths
accurate
Disadvantages:
high cost instrument
radioactive licensing and safety
not reliable for shallow measurements near the soil surface
Dielectric constant
A soil’s dielectric constant is dependent on soil moisture
Time domain reflectometry (TDR)
Frequency domain reflectometry (FDR)
Primarily used for research purposes at this time
Soil Water MeasurementSoil Water Measurement (cont..)(cont..)
60. Tensiometers
Measure soil water potential (tension)
Practical operating range is about 0 to 0.75 bar of
tension (this can be a limitation on medium- and fine-
textured soils)
Electrical resistance blocks
Measure soil water potential (tension)
Tend to work better at higher tensions (lower water
contents)
Thermal dissipation blocks
Measure soil water potential (tension)
Require individual calibration
Soil Water MeasurementSoil Water Measurement (cont..)(cont..)
61. Porous Ceramic Tip
Vacuum Gauge (0-100 centibar)Vacuum Gauge (0-100 centibar)
Water ReservoirWater Reservoir
Variable Tube Length (12 in- 48 in)
Based on Root Zone Depth
Tensiometer for Measuring Soil Water PotentialTensiometer for Measuring Soil Water Potential
64. Chapter-4Chapter-4
4. Irrigation water requirement and scheduling4. Irrigation water requirement and scheduling
4.1. Introduction
• The irrigation system is usually not expected to supply all of the
moisture required for maximum crop production. To do so would
ignore the valuable contribution of other water sources such as rain
and thereby force the irrigation system to be larger and more
expensive than necessary.
• In arriving at the contribution an irrigation system will make to an
irrigated area, particularly a surface irrigation system, four major
factors require consideration. These are:
The concept of water balance in the region encompassing the plant
environment
The body of soil supplying moisture, nutrient, and anchorage for the
crop and the associated characteristics of this porous medium
The crop water requirements, including drainage for aeration and
salt leaching
The efficiency and uniformity of the irrigation system
65. 4.2. Water balance
• The employment of a water balance is a useful concept for
characterizing, evaluating, or monitoring any surface irrigation system.
A schematic of the water balance parameters used for characterizing a
surface-irrigated field is shown in Fig. 4.1. The terms are defined as:
• Da = depth of applied irrigation water
• D∆s = depth of change in soil moisture storage in the root zone where
D∆s is positive for increasing soil moisture storage
• Ddp = depth of deep percolation
• De = depth of evaporation from soil surface or ponded water surface
• Det = depth of evapotranspiration
• Dgw = depth of capillary rise from the groundwater table entering the
root zone
• Dp = depth of precipitation
• Dpl = depth of precipitation intercepted by the plants (crop)
66. • Dpz = depth of precipitation that infiltrates into the soil
• Dt = depth of transpiration from plants
• Dtw = depth of tail water (surface) runoff resulting from
overland flow of the irrigation water supply
• Dz = depth of infiltrated water resulting from overland flow
of the irrigation water supply
• There are two additional terms that are useful to define at this
point:
• Dpn = depth of net precipitation, or the depth of precipitation
that is made available to the plant system
• Dd = depth of drainage requirement for maintaining a salt
balance in the root zone
67. • Figure 4.1: The water balance parameters for a surface-irrigated field.
68. • The principle of continuity requiresThe principle of continuity requires that inflow (I) minus
outflow (O) equals the change in storage (∆S) within the
defined boundaries of a system:
• Of primary concern in surface irrigation are boundaries A, B,
C, and D as shown in Fig. 4.1, for which the continuity
equation can be written as
• in which
• And
I O S− = ∆
( ) ( )a gw p et pr tw dp pl s
Inflows Outflows
D D D D D D D D D∆+ + − + + + + =
a z twD D D= + p pz pl prD D D D= + +
et e tD D D= +
69. 4.3. Crop water requirement
• Crop water requirement is defined as the depth of waterthe depth of water
(mm) needed to raise crop in a given period.(mm) needed to raise crop in a given period.
• It comprises of the water lost through evaporation from crop
field, water transpired and metabolically used by crop
plants, water lost during application which is economically
unavailable and the water used for salt leaching and so on.
• Determination of crop water requirement is used for the
planning, design, and operation of both rain fed and
irrigated agriculture.
70. 4.4. Evapotranspiration4.4. Evapotranspiration
• The concept of crop evapotranspiration (ETc) is intimately
connected with CWR.
• It is defined as the rate of ET (mm/day) of a given crop as
influenced by its growth stages, environmental conditions, and
crop management.
• To determine the crop ET, the reference evapotranspiration
(ET0) is used and it refers to a reference crop cultivated in
reference conditions such that its rate of ET (mm/day) reflects
the climatic conditions characterizing the local environment.
• The transfer from ET0 to ETc is done by adopting the crop
coefficients (Kc), which represents the ratio between the rates
of ET of the cultivated crop and of the reference crop, that is,
Kc =ETc/ET0.
71. • For irrigated crops, another main concept is the irrigation
water requirement (IWR), defined as the net depth of water
(mm) that is required to be applied to a crop to fully satisfy its
specific CWR. The IWR is the fraction of CWR not satisfied
by rainfall, soil water storage, and groundwater contribution.
• The rate and amount of ET is the core information needed to
design irrigation projects, and it is also essential for managing
water quality and other environmental concerns.
• Anyone involved with resource management will likely need
to understand the methods available for estimating
evapotranspiration.
72. Figure 4.2: Sub-processes in evapotranspiration
Evaporation essentially occurs on the surfaces of open water
such as lakes, reservoirs, or puddles, or from vegetation and
ground surfaces. Transpiration involves the removal of water
from the soil by plant roots, transport of the water through the
plant into the leaf, and evaporation of the water from the leaf
interior into the atmosphere.
Evaporation Transpiratio
n
Open water Soil Vegetation surfaces Plants
73. Transpiration Ratio and Consumptive UseTranspiration Ratio and Consumptive UseTranspiration Ratio and Consumptive UseTranspiration Ratio and Consumptive Use
• Two terms frequently used relating to transpiration are
transpiration ratio and consumptive use.
Transpiration ratio is the ratio of the weight of water
transpired to the weight of dry matter produced by the plant.
This ratio is a measure of how efficiently crops use water.
For example, the transpiration ratios are approximately 900 for
alfalfa, 640 for potatoes, 500 for wheat, 450 for red clover, 350
for corn and 250 for sorghum.
The least efficient crop, in terms of water use, would be alfalfa
because it uses 900 kilograms of water for every kilogram of
dry alfalfa it produces. Sorghum is the most efficient crop
listed because it uses only 250 kg of water for every kg of dry
matter produced.
74. • Consumptive use is the total amount of water needed
to grow a crop (the sum of the water used in
evapotranspiration plus the water stored in the plant's
tissues). The term consumptive use is generally used
interchangeably with evapotranspiration because the
amount of water retained in plant tissue is negligible
compared to the amount of evapotranspiration.
75. 4.54.5 Potential EvapotranspirationPotential Evapotranspiration4.54.5 Potential EvapotranspirationPotential Evapotranspiration
• Evaporation and especially evapotranspiration are complex
processes because the rate of water vapor loss depends on the
amount of solar radiation reaching the surface, the amount of wind,
the opening of the stomates, the soil water content, the soil type and
the type of plant.
• In order to simplify the situation, researchers have attempted to
remove all the unknowns such as aperture of the stomates and soil
water content, and focus on climatic conditions.
• The simplified calculations are termed potential evaporation and
potential evapotranspiration. The definition given by Jensen et al.
(1990) for potential evaporation (Ep) is the "...evaporation from a
surface when all surface-atmosphere interfaces are wet so there is no
restriction on the rate of evaporation from the surface.
76. • The magnitude of Ep depends primarily on atmospheric
conditions and surface albedo but will vary with the surface
geometry characteristics such as aerodynamic roughness".
Surface albedo is the proportion of solar radiation which is
reflected from a soil and crop and crop surface.
• Potential evapotranspiration (ETp)
was originally defined as " the amount of water transpired in
unit time by a short green crop, completely shading the
ground, of uniform height and never short of water."
• The crop is assumed to be short and uniform, and completely
shading the ground so that no soil is exposed. The crop is
never short of water, so soil water content is no longer a
variable and presumably (most probably) the stomates would
always be fully open. These conditions theoretically provide
the maximum evapotranspiration rate based on the given
climatic conditions.
77. • Many authors treat potential evapotranspiration and potential
evaporation as synonymous but the original intent was that potential
evapotranspiration involved on actively growing crop and potential
evaporation did not.
4.6. Actual Evapotranspiration4.6. Actual Evapotranspiration
• Potential evapotranspiration and evaporation may be easier to estimate
but do not represent reality. In general, watersheds are not entirely
covered by well-watered short green crops.
• Actual evapotranspiration (ET) or actual evaporation (E) is the amount
or rate of ET occurring from a place of interest and it is the value we
want to estimate. In practice, actual ET is obtained by first calculating
potential evapotranspiration and then multiplying by suitable crop
coefficients to estimate the actual crop evapotranspiration.
• Crop coefficients are usually residual terms from a statistical analysis
of field data, so it is essential that the methods for estimating potential
evapotranspiration be consistent with the crop coefficients.
78. • some studies have used alfalfa and some have used grasses to
measure potential evapotranspiration. Other methods correlate
evaporation from free water surfaces to actual ET. The result is
that the methods for determining actual ET are variable and
confusing. Scientists have attempted to remedy this problem by
introducing reference crop evapotranspiration.
4.7. Reference Crop Evapotranspiration
• Reference crop evapotranspiration (ETr) is defined as "...the rate
at which water, if available, would be removed from the soil and
plant surface of a specific crop, arbitrarily called a reference
crop”.
• Typical reference crops are grasses and alfalfa. The crop is
assumed to be well-watered with a full canopy cover (foliage
completely shading the ground). The major advantage of relating
ETr to a specific crop is that it is easier to select consistent crop
coefficients and to calibrate reference equations in new areas.
79. 4.8. Measuring Evaporation or Evapotranspiration4.8. Measuring Evaporation or Evapotranspiration4.8. Measuring Evaporation or Evapotranspiration4.8. Measuring Evaporation or Evapotranspiration
• There are several methods available for measuring evaporation or
evapotranspiration.
• Since vapor flux is difficult to measure directly, most methods measure
the change of water in the system. Figure 4.3 shows schematically
options available for measuring potential evaporation, potential
evapotranspiration, or actual evapotranspiration.
• An evaporation pan or ET gage can be used to measure potential
evapotranspiration. Actual evapotranspiration can be measured in
several ways.
• If you need a simpler, less expensive technique, measuring soil water
depletion or using a water balance would be possibilities. More precise,
but also more complex methods include lysimeters, either weighing or
non-weighing, or using an energy balance or mass transfer technique.
80. Figure 4.3: Options available for measuring potential or actual
evapotranspiration
Actual ET
Simpler, less
expensive
More complex
and expensive
Soil water
depletion
Water
balance
Lysimeters Energy
balance
Mass
transfer
Weighing Non-weighing
Percolation Constant water table
Potential ET
Pan
evaporation
ET Gage
81. Soil Water Depletion
Lysimeters
Empirical methods
Soil conservation service modified Blaney-Criddle
FAO Modified Blaney-Criddle
Pan Evaporation
Combination Method
Penman Method
FAO Modified Penman Method
82. 4.9. Depth of Irrigation4.9. Depth of Irrigation
• In planning and managing irrigation, the soil’s capacity to store
available water can be thought of as the soil water reservoir, which
must be filled periodically by irrigation or rainfall.
It is slowly depleted by evapotranspiration. Water application in
excess of the reservoir capacity is wasted unless it is required for
leaching or to meet a specific management need.
Irrigation must be scheduled to prevent the soil water reservoir from
becoming so low as to inhibit plant growth.
• The difference between FC and PWP is the available water (AW)
and can be estimated from
• Where.
AW = (FCv–PWPv)Dr/100
83. FCv and PWPv= the volumetric field capacity and permanent wilting
point percentages, respectively,
Dr = depth of the root zone or depth a layer of soil with in the root
zone (L)
AW = depth of water available to plants (L)
Plants can remove only a portion of the available water before
growth and yield are affected.
This portion is readily available water (RAW) and for most crops
ranges between 40 and 65 percent of AW in the root zone. Readily
available water can be estimated from
RAW = (MAD)(AW)
In which MAD is the management allowed deficiency or the portion
(decimal) of the available water that management determines can be
removed from the root zone without adversely affecting yield and/or
economic return.
84. • The supply requirements at the field level are determined by the
depth and interval of irrigation. These data can be obtained from the
soil water balance and are primarily determined by:
i. the total available soil water (Sa = Sfc – Sw where Sfc and Sw are the
soil water content in mm/m soil depth at field capacity and
wilting point, respectively);
ii. the fraction of available soil water permitting unrestricted
evapotranspiration and/or optimal crop growth; and
iii. the rooting depth (D). The depth of irrigation application (d)
including application losses is:
and frequency of irrigation expressed as irrigation interval of the
individual field (i) is:
( ). .
.a
a
p s D
d mm
E
=
( ). ap s D
i days
ET
=
85. • where:
p = fraction of available soil water permitting unrestricted
evapotranspiration, fraction
Sa = total avalable soil water, mm/m soil depth
D = rooting depth, m
Ea = application efficiency, fraction
• Since p, D and ET will vary over the growing season, the depth in
mm and interval of irrigation in days will vary.
• For design and operation of the water distribution system, the
requirements of the individual fields will need to be expressed in
flow rates or stream size (q in m3
/sec) and supply duration (t in
seconds, hours or days). The field supply (q.t) is:
( ) 310
. . . .a
a
q t p s D A m
E
=
86. where:
q = stream size, m3
/sec
t = supply duration, seconds
Ea = application efficiency, fraction
p = fraction of available soil water permitting unrestricted
evapotranspiration, fraction
Sa = total available soil water, mm/m soil depth
D = rooting depth, m
A = acreage, ha
In determining the relative values of q and t, the soil intake rate and
method of irrigation must be taken into account. For instance, t will
be greater for heavy as compared to light soil and also sprinkler and
furrow irrigation as compared to basin. Furthermore, the stream size
(q) must be handled easily by the irrigator.
87. • Field irrigation requirements will vary for each crop during the
growing season and the supply must follow those changes over area
and time. Analysis of the system and selection of the method of
supply (continuous, rotation or demand) should therefore start with
an evaluation of the field variables.
• Example: A clay soil having an average field capacity (FC) and
permanent wilting point (PWP) of 47.2 and 30.1%, respectively at
the first 45 cm of the soil profile is planted to corn. If actual
evapotranspiration (AET) is 6.2 mm/d, irrigation interval is 1 week
and application efficiency is 65%, find the following:
A, Available water in the root zone (AW) if apparent specific gravity
(As) is 1.2,
B, Depth of irrigation (DI) based on allowable depletion (MAD) of
50% and application efficiency (Ea) of 65%
C, Depth of irrigation based on consumptive use (AET) and irrigation
interval
88. • Solution:
A) Available water in the root zone (AW),
Aw = (FC-PWP)/100 *As*Dr
= (47.2-30.1)/100 *1.2*0.45
= 0.092m
= 92 mm
b) Depth of irrigation (DI) based on allowable depletion (MAD)
Readily available water in the root zone (RAW)
RAW = AW*MAD
= 92 mm*0.5
= 46mm
DI = RAW/Ea
= 46mm/0.65
= 71 mm
• c) Depth of irrigation based on consumptive use (AET) and irrigation
interval
DI = AET*I/Ea
= 6.2mm/d*7d/0.65
= 67mm
89. 4.10. Crop Coefficient Curves4.10. Crop Coefficient Curves
• FAO Crop Coefficient Method
• The FAO methods, all modifications of the Penman equation, and many
other evapotranspiration estimating methods result in an
evapotranspiration estimate for a reference surface of water or
reference crop of grass or alfalfa. To determine water use for a crop
other than the reference, crop coefficients must be applied. This is
demonstrated by the following equation:
ETc = KcETr
where
ETc = crop evapotranspiration
Kc = crop coefficient
ETr = reference evapotranspiration
90. • the Kc values have to be with respect to the same crop as the ETr
values used in the equation.
• The FAO method divides the crop coefficient curve into four linear
line segments which approximate the curve. The first step is to
divide the growth season into the following growth periods:
1. Initial period1. Initial period:: Time of planting to time of 10 percent ground cover.
2. Crop development period2. Crop development period:: From end of initial period to time of
effective full cover – that is, 70 to 80 percent ground cover.
3. Mid-season period3. Mid-season period:: From end of crop development period to start of
plant maturity as indicated by leaf discoloration (e.g., beans, maize),
leaves falling off (e.g., cotton), or leaves curling and discolouring
(e.g., tomatoes, potatoes).
4. Late season period4. Late season period:: From end of mid-season period to time of full
maturity or harvest.
91. • After the season has been divided into the four growth periods,
coefficients must be determined corresponding to the initial, mid-
and late season periods to allow plotting of the total seasonal Kc
function. The initial period crop coefficient, Kci, is related to the
evaporation from basically a bare soil. This coefficient is a function
of soil wetness and the reference evapotranspiration rate during the
initial period.
Fig. Generalised crop
coefficient curve
92. Irrigation Methods are mainly classified into
:
1. Surface Irrigation or Gravity Irrigation
2. Subsurface Irrigation or Sub-irrigation
3. Sprinkler or overhead irrigation
4. Drip or Trickle irrigation
◦
93. 1) SURFACE IRRIGATION
Irrigation water flows across the field to the point of
infiltration
Primarily used for field crops and orchards
Water is applied to the soil surface and the water flows by
gravity either through furrows, strips or basins.
Water is applied from a channel located at the upper reach
of the field.
Loss of water by conveyance and deep percolation is high
and the efficiency of irrigation is only 40-50% at field level
in surface method of irrigation.
Properly constructed water distribution systems to give
sufficient control of water to the fields
And effective land preparation to permit uniform
distribution of water over the field are very important.
94. Water is applied to the field in either the controlled or
uncontrolled manner.
Controlled: Water is applied from the head ditch and
guided by corrugations, furrows, borders, or ridges.
Uncontrolled: Wild flooding.
Surface irrigation is entirely practised where water is
abundant.
Low initial cost of development is later offset by high
labour cost of applying water.
Deep percolation, runoff and drainage problems
97. Furrow irrigation - in which the water poured
on the field is directed to flow through narrow
channels dug between the rows of crops,
instead of distributing the water throughout
the whole field evenly.
The furrows must all have equal dimensions,
in order to guarantee that the water is
distributed evenly.
Like flood irrigation, furrow irrigation is rather
cheap in areas where water is inexpensive.
101. In furrow irrigation, only a part of the land
surface (the furrow) is wetted thus minimizing
evaporation loss.
Irrigation can be by corrugation using small
irrigation streams.
Furrow irrigation is adapted for irrigating on
various slopes except on steep ones because of
erosion and bank overflow.
102. There are different ways of applying water to the furrow.
As shown in Fig 3.1, siphons are used to divert water
from the head ditch to the furrows.
There can also be direct gravity flow whereby water is
delivered from the head ditch to the furrows by cutting
the ridge or levee separating the head ditch and the
furrows.
Gated pipes can also be used. Large portable pipe(up
to 450 mm) with gate openings spaced to deliver water
to the furrows are used.
Water is pumped from the water source in closed
conduits.
The openings of the gated pipe can be regulated to
control the discharge rate into the furrows.
106. The Specific Design Parameters of Furrow
Irrigation Are Aimed at Achieving the Above
Objectives and Include:
a) Shape and Spacing of Furrows:
Heights of ridges vary between 15 cm and 40
cm and the distance between the ridges
should be based on the optimum crop
spacing modified, if necessary to obtain
adequate lateral wetting, and to
accommodate the track of mechanical
equipment.
The range of spacing commonly used is from
0.3 to 1.8 m with 1.0 m as the average.
109. In this, Parallel ridges are made to guide a sheet of flowing
water when the water moves down the slope.
The field is divided into several long parallel strips called
borders that are separated by low ridges.
Field should be even surface over which the water can flow
down the slope with a nearly uniform depth.
Every strip is independently irrigated by turning a stream of
water at the upper end.
Then water spreads and flows down the strip in a thin sheet.
Water moves towards the lower end without erosion covering
the entire width of the border.
Sufficient moisture is provided to the soil to entire length of the
border.
Border method is suitable for most of the soils, while it is best
suited for soils having moderately low to high infiltration rates.
However, it is not suitable for course sandy and clay textured
soils.
110. Border Irrigation SystemBorder Irrigation System
In a border irrigation, controlled surface flooding is
practised whereby the field is divided up into strips by
parallel ridges or dykes and each strip is irrigated
separately by introducing water upstream and it
progressively covers the entire strip.
Border irrigation is suited for crops that can withstand
flooding for a short time e.g. wheat.
It can be used for all crops provided that the system
is designated to provide the needed water control for
irrigation of crops.
It is suited to soils between extremely high and very
low infiltration rates.
113. Border Irrigation Contd.Border Irrigation Contd.
In border irrigation, water is applied slowly.
The root zone is applied water gradually
down the field.
At a time, the application flow is cut-off to
reduce water loses.
Ideally, there is no runoff and deep
percolation.
The problem is that the time to cut off the
inflow is difficult to determine.
115.
Basin method of irrigation is adopted mainly in
orchards.
Usually round basins are made for small trees and
square basin for large trees.
These basins allow more water to be impounded as the
root zones of orchard plants are usually very deep.
Each basin is flooded and water is allowed to infiltrate
into the soil.
Based on type of crop and soil, nearly 5-10 cm depth of
water may be needed for every irrigation.
The advantage of basin method is that unskilled labour
can be used as there is no risk of erosion.
Disadvantages : there is difficulty in using modern
machinery and it is also labour intensive.
118. Basin irrigation is suitable for many field crops.
Rice grows best when its roots are submerged in water
and so basin irrigation is the best method to use for this
crop.
Other crops which are suited to basin irrigation include:
Pastures, e.g. alfalfa, clover;
Citrus, banana;
Crops which are broadcast, such as cereals, and
To some extent row crops such as tobacco.
120. Size of BasinsSize of Basins
The size of basin is related to stream size and soil type(See
Table below).
Table : Suggested basin areas for different soil types and rates of water flow
Flow rate Soil Type
Sand Sandy loam Clay loam Clay
l/s m3
/hr .................Hectares................................
30 108 0.02 0.06 0.12
0.20
60 216 0.04 0.12 0.24
0.40
90 324 0.06 0.18 0.36
0.60
120 432 0.08 0.24 0.48
0.80
150 540 0.10 0.30 0.60
1.00
180 648 0.12 0.36 0.72
1.20
210 756 0.14 0.42 0.84
1.40
240 864 0.16 0.48 0.96
1.60
300 1080 0.20 0.60 1.20
2.00
Note: The size of basin for clays is 10 times that of sand as the infiltration rate for clay is low
leading to higher irrigation time. The size of basin also increases as the flow rate increases. The
table is only a guide and practical values from an area should be relied upon. There is the need for
field evaluation.
121. Most common among surface irrigation
Suitable for close growing crops like groundnut,
wheat, finger millet, pearl millet, paragrass etc.
In this method field is divided into small plots
surrounded by bunds on all four sides.
Water from head channel is supplied into the field
channel one after the other.
Each field channel supplies water to two rows of
check basins and water is applied to one basin after
other.
122. In this, field is laid out into long, narrow,
strips, bordering with small bunds.
Most common size of strips are 30-50 m
length and 3-5 m width.
Borders are laid out along the general slope.
Water from the channel is allowed into each
strip at a time.
This method is suitable for close growing
crops and medium to heavy textured soils.
Not suitable for sandy soils.
123. It should be applied only to flat lands that do not
concave or slope downhill so that the water can
evenly flow to all parts of the field.
Yet even so, about 50% of the water is wasted
and does not get used by the crops.
Some of this wasted water accumulates at the
edges of a field and is called run-off.
In order to conserve some of this water, growers
can trap the run-off in ponds and reuse it during
the next round of flood irrigation.
124. In flood irrigation, a large amount of
water is brought to the field and flows
on the ground among the crops.
In regions where water is abundant,
flood irrigation is the cheapest
method
This low tech irrigation method is
commonly used by societies in
developing countries.
125. However a large part of the wasted water can not be
reused due to massive loss via evaporation and
transpiration.
One of the advantages of flood irrigation is its ability to
flush salts out of the soil, which is important for many
saline intolerant crops.
However, the flooding causes an anaerobic environment
around the crop which can increase microbial conversion
of nitrogen from the soil to atmospheric nitrogen, or
denitrification, thus creating low nitrogen soil.
Surge flooding is an attempt at a more efficient version
of conventional flood irrigation in which water is released
onto a field at scheduled times, thus reducing excess
run-off.
126. - Irrigation to crops by applying water from
beneath the soil surface either by
constructing trenches or installing
underground perforated pipe lines.
In this system, water is discharged into
trenches.
And allowed to stand during the whole
period of irrigation for lateral and upward
movement of water by capillarity to wet
the soil between the trenches.
127. Conditions that favor subsurface irrigation
An impervious subsoil at a depth of 2 m or more.
A very permeable subsoil of reasonably uniform texture
permitting good lateral and upward movement of water.
Permeable loam or sandy loam surface soil.
Uniform topographic conditions and moderate slope.
Existence of high water table.
Irrigation water is scarce and costly.
Soils should be free of any salinity problem.
It must be ensured that no water is lost by deep percolation.
Subsurface irrigation is made by constructing a series of
ditches or trenches 60 to 100 cm deep.
Width of the trenches is about 30 cm and vertical.
Spacing between the trenches varies between 15 to 30 m
depending on soil types and lateral movement of water in soils.
128. Various types of crops, particularly with shallow root
systems are well adapted to subsurface irrigation
system.
Wheat, potato, beet, peas, fodder crops etc.
Advantages
Maintenance of soil water at favorable tension
Loss of water by evaporation is held at minimum
Can be used for soils with low water holding
capacity and high infiltration rate where surface
irrigation methods cannot be adopted and sprinkler
irrigation is expensive.
129. Presence of high water table.
Poor quality irrigation water cannot be
used-good quality water must be available.
Chances of saline and alkali conditions
being developed by upward movement of
salts with water.
Soils should have a good hydraulic
conductivity for upward movement of
water.
130. Sprinkler irrigation is a method of applying irrigation water
which is similar to natural rainfall.
Water is distributed through a system of pipes usually by
pumping.
Water under pressure is carried and sprayed into the air
above the crop through a system of:
Overhead perforated pipes, nozzle lines, or through nozzles
fitted to riser pipes attached to a system of pipes laid on the
ground.
Nozzles of fixed type or rotating under the pressure of water
are set at suitable intervals in the distribution pipes.
Sprayed water wets both the crop and the soil and, hence,
has a refreshing effect.
Water is applied at a rate less than the intake rate
of soil so that there is no runoff.
Measured quantity of water is applied to meet the
soil water depletion.
132. Sprinkler irrigation is suited for most row, field and tree
crops and water can be sprayed over or under the crop
canopy.
Large sprinklers are not recommended for irrigation of
delicate crops such as lettuce because the large water
drops may damage the crop.
Suitable slopes
Sprinkler irrigation is adaptable to any farmable slope,
whether uniform or undulating.
Lateral pipes supplying water to the sprinklers should
always be laid out along land contour.
This will minimize the pressure changes at the sprinklers
and provide a uniform irrigation.
133. Sprinklers are best suited to sandy soils
with high infiltration rates although they
are adaptable to most soils.
Application rate from the sprinklers (in
mm/hour) is always chosen to be less
than the basic infiltration rate of the soil -
so that surface ponding and runoff can be
avoided.
Sprinklers are not suitable for soils which
easily form a crust.
134. A typical sprinkler irrigation system consists of the
following components:
Pump unit
Mainline
Laterals
Sprinklers
Suitable irrigation water
A good clean supply of water, free of suspended
sediments, to avoid problems of sprinkler nozzle
blockage and spoiling the crop by coating it with
sediment.
136. 136
Sprinkler irrigation: Criteria
• Must permit cost recovery within one to two
years (and double investment in a short time)
• Must be suitable for use on small and irregular
shaped plots
• Must require only simple maintenance and tools
• Have a low risk of component failure
• Be simple to operate
• Be durable and reliable – able to withstand
rough and frequent handling without serious
damage
157. Lateral DischargeLateral Discharge
The Discharge (QL) in a Lateral is defined
as the flow at the head of the lateral
where water is taken from the mainline
or submain.
Thus: QL = N. qL Where N is the number
of sprinklers on the lateral and qL is the
Sprinkler discharge (m3
/h)
158. Pressure at Head of LateralPressure at Head of Lateral
The Pressure requirements (PL)where the
Lateral joins the Mainline or Submain are
determined as follows:
PL = Pa + 0.75 Pf + Pr For laterals laid on
Flat land
PL = Pa + 0.75 (Pf Pe) + Pr For Laterals
on gradient.
The factor 0.75 is to provide for average
operating pressure (Pa) at the centre of the
Lateral rather than at the distal end. Pr is the
height of the riser.
±
159. Pumping RequirementsPumping Requirements
Maximum Discharge (Qp) = qs N
Where:
qs is the Sprinkler Discharge and
N is the total number of Sprinklers operating at
one time during irrigation cycle.
The Maximum Pressure to operate the system
(Total Dynamic Head, Pp) is given as shown in
Example.
160. DRIP OR TRICKLE IRRIGATIONDRIP OR TRICKLE IRRIGATION
Introduction: In this irrigation system:
i) Water is applied directly to the crop ie. entire field is
not wetted.
ii) Water is conserved
(iii) Weeds are controlled because only the places
getting water can grow weeds.
(iv) There is a low pressure system.
(v) There is a slow rate of water application somewhat
matching the consumptive use. Application rate can be
as low as 1 - 12 l/hr.
(vi) There is reduced evaporation, only potential
transpiration is considered.
vii) There is no need for a drainage system.
161. Drip irrigation / trickle irrigation - involves dripping
water onto the soil at very low rates (2-20
litres/hour)
-from a system of small diameter plastic pipes
fitted with outlets called emitters or drippers.
Water is applied close to plants so that only part of
the soil in which the roots grow is wetted (Figure
60 in Notes).
With drip irrigation water, applications are more
frequent (usually every 1-3 days).
This provides a very favourable high moisture
level in the soil in which plants can flourish.
163. 163
Water Use for Trickle Irrigation System
• The design of drip system is similar to that of
the sprinkler system except that the spacing of
emitters is much less than that of sprinklers
and that water must be filtered and treated to
prevent blockage of emitters.
• Another major difference is that not all areas
are irrigated.
• In design, the water use rate or the area
irrigated may be decreased to account for this
reduced area.
167. While drip irrigation may be the most expensive method of irrigation, it is
also the most advanced and efficient method in respect to effective
water use.
Usually used to irrigate fruits and vegetables
System consists of perforated pipes that are placed by rows of crops or
buried along their root lines and emit water directly onto the crops that
need it.
As a result, evaporation is drastically reduced and 25% irrigation water
is conserved in comparison to flood irrigation.
Drip irrigation also allows the grower to customize an irrigation program
most beneficial to each crop.
Fertigation is possible.
Caution : Water high in salts / sediments should be filtered - otherwise
they may clog the emitters and create a local buildup of high salinity soil
around the plants if the irrigation water contains soluble salts.
168. Drip irrigation is most suitable for row
crops (vegetables, soft fruit), tree and
vine crops where one or more emitters
can be provided for each plant.
Generally only high value crops are
considered because of the high capital
costs of installing a drip system.
169. Drip irrigation is adaptable to any
farmable slope.
Normally the crop would be planted
along contour lines and the water
supply pipes (laterals) would be laid
along the contour also.
This is done to minimize changes in
emitter discharge as a result of land
elevation changes.
170. Drip irrigation is suitable for most soils.
On clay soils water must be applied slowly
to avoid surface water ponding and runoff.
On sandy soils higher emitter discharge
rates will be needed to ensure adequate
lateral wetting of the soil.
171. One of the main problems with drip irrigation is blockage of
the emitters.
All emitters have very small waterways ranging from 0.2-
2.0 mm in diameter and these can become blocked if the
water is not clean.
Thus it is essential for irrigation water to be free of
sediments.
]If this is not so then filtration of the irrigation water will be
needed.
Blockage may also occur if the water contains algae,
fertilizer deposits and dissolved chemicals which precipitate
such as Ca and Fe.
Filtration may remove some of the materials but the
problem may be complex to solve and requires an
experienced professional.
172. SOIL TYPE AND WATER MOVEMENT.
THE APPLICATION OF WATER IS BY
DRIPPERS
172
173. A typical drip irrigation system is
shown in Figure 61 and consists of
the following components:
Pump unit
Control head
Main line
Laterals
Emitters or drippers.
174. Pump unit takes water from the source and provides
the right pressure for delivery into the pipe system.
The control head consists of valves to control the
discharge and pressure in the entire system.
It may also have filters to clear the water.
Common types of filter include screen filters and graded
sand filters which remove fine material suspended in the
water.
Some control head units contain a fertilizer or nutrient
tank.
These slowly add a measured dose of fertilizer into the
water during irrigation.
This is one of the major advantages of drip irrigation over
other methods.
175. Supply water from the control head into the fields.
They are usually made from PVC or polyethylene hose and
should be buried below ground because they easily degrade
when exposed to direct solar radiation.
Lateral pipes are usually 13-32 mm diameter.
Emitters or drippers are devices used to control the discharge of
water from the lateral to the plants.
They are usually spaced more than 1 metre apart with one or
more emitters used for a single plant such as a tree.
For row crops more closely spaced emitters may be used to wet
a strip of soil.
Many different emitter designs have been produced in recent
years.
The basis of design is to produce an emitter which will provide a
specified constant discharge which does not vary much with
pressure changes, and does not block easily.
176. The water savings that can be made using drip
irrigation are the reductions in deep percolation, in
surface runoff and in evaporation from the soil.
These savings, it must be remembered, depend as
much on the user of the equipment as on the
equipment itself.
Drip irrigation is not a substitute for other proven
methods of irrigation.
It is just another way of applying water.
It is best suited to areas where water quality is
marginal, land is steeply sloping or undulating and of
poor quality, where water or labour are expensive, or
where high value crops require frequent water
applications.
177. Water Use for Trickle IrrigationWater Use for Trickle Irrigation
SystemSystem Contd.Contd.
Karmeli and Keller (1975) suggested the
following water use rate for trickle irrigation design
ETt
= ET x P/85
Where: ETt
is average evapotranspiration rate for crops under
trickle irrigation;
P is the percentage of the total area shaded by crops;
ET is the conventional evapotranspiration rate for the crop. E.g.
If a mature orchard shades 70% of the area and the
conventional ET is 7 mm/day, the trickle irrigation design rate is:
7/1 x 70/85 = 5.8 mm/day
OR use potential transpiration, Tp
= 0.7 Epan
where Epan
is the
evaporation from the United States Class A pan.
178. EmittersEmitters
Consist of fixed type and variable size types.
The fixed size emitters do not have a
mechanism to compensate for the friction
induced pressure drop along the lateral while
the variable size types have it.
Emitter discharge may be described by:
q = K h x
Where: q is the emitter discharge; K is
constant for each emitter ; h is pressure head
at which the emitter operates and x is the
exponent characterized by the flow regime.
179. Water Distribution from EmittersWater Distribution from Emitters
Emitter discharge variability is greater than that of
sprinkler nozzles because of smaller openings(lower
flow) and lower design pressures.
Eu = 1 - (0.8 Cv/ n 0.5
)
Where Eu is emitter uniformity; Cv is manufacturer's
coefficient of variation(s/x ); n is the number of
emitters per plant.
Application efficiency for trickle irrigation is
defined as:
Eea
= Eu x Ea x 100
Where Eea
is the trickle irrigation efficiency; Ea is the
application efficiency as defined earlier.
180. Pressure Head at Manifold InletPressure Head at Manifold Inlet
Like Sprinklers, the pressure head at inlet to
the manifold:
= Average Operating Head = 8.9 m
+ 75% of Lateral and Manifold head Loss =
0.75 (0.51 + 0.68)
+ Riser Height = Zero for Trickle since no risers
exist.
+ Elevation difference = Zero , since the field is
Level
= 9.79 m
181. Solution ConcludedSolution Concluded
Total Head for Pump
= Manifold Pressure = 9.79 m
+ Pressure loss at Sub-main = 6.59 m
+ Pressure loss at Main = 2.90 m
+ Suction Lift = 20 m
+ Net Positive Suction head for pump = 4 m
(assumed)
= 43.28 m
i.e. The Pump must deliver 3.23 L/s at a head of
about 43 m.
182. SUB-SURFACE IRRIGATIONSUB-SURFACE IRRIGATION
Applied in places where natural soil and
topographic condition favour water
application to the soil under the surface, a
practice called sub-surface irrigation.
These conditions include:
a) Impervious layer at 15 cm depth or
more
b) Pervious soil underlying the restricting
layer.
c) Uniform topographic condition
d) Moderate slopes.
183. SUB-SURFACE IRRIGATIONSUB-SURFACE IRRIGATION (Contd…)(Contd…)
The operation of the system involves a
huge reservoir of water and level is
controlled by inflow and outflow.
The inflow is water application and rainfall
while the outflow is evapotranspiration
and deep percolation.
It does not disturb normal farm
operations. Excess water can be removed
by pumping.