Irrigation - Gardens

Course CodeBHT210
Fee CodeS2
Duration (approx)100 hours
QualificationStatement of Attainment

Learn Irrigation Design and Installation

Learn about irrigation technique: estimating plant needs, operations, scheduling, pumps, filters, systems, drainage, and more.

  • Learn about the equipment and techniques used for plant watering
  • Learn to irrigate plants in gardens, plant nurseries, indoors, greenhouses, etc.
  • Become a better gardener, nurseryman or horticulturist

Lesson Structure

There are 10 lessons in this course:

  1. Introduction to Irrigation
    • Objective of irrigation
    • A wider view
    • Water sources
    • Improving water quality
    • Water quality problems
    • Physical impurities -sediment. turbidity, colour
    • Chemical impurities -hardness, alkalinity, corrosion, iron, salinity, tastes and odours
    • Biological impurities - algae, microorganisms
  2. Lesson 2 Soil Characteristics
    • Understanding soils - sand, silt, clay, organic material
    • Naming the soil
    • Different soils for different purposes
    • Improving soils
    • Chemical soil properties - pH, sodicity, salinity
    • Physical soil properties - uniformity, available soil water capacity, infiltration, internal drainage
    • Kinds of soil moisture
    • Gravitational water
    • Capillary water
    • Hygroscopic water
    • Transpiration and Wilting Point
    • Feel test for estimating soil moisture
    • Fertigation
  3. 3. Estimating Plant Needs and Irrigation Scheduling
    • When to irrigate
    • Symptoms of water deficiency
    • Symptoms of water excess
    • Checklist for home gardeners
    • Timing of irrigations
    • Measuring water available to plants
    • Calculating field capacity
    • Calculating permanent wilting point
    • Available moisture range
    • Rooting depths of selected plants
    • Water extraction by roots
    • irrigation calculations
    • Irrigation system efficiency
    • Estimating water needs
    • Estimated water loss under different climatic conditions
    • Tensiometers
    • Water requirements of turf grasses
    • Importance of schedules
    • Water volumes and duration
  4. Drainage
    • Reasons for drainage
    • Improving permeability during construction
    • Cultivation
    • Adding soil ameliorants
    • Chemical treatments
    • Improving surface drainage after construction -sand slitting, aerating, sub soiling
    • Drain layout - herringbone, grid
    • Outlet
    • Gradients
    • Distance between pipes
    • Drain depth
    • Drain types
    • Laing drains
    • Dams and water storage -site choice, size
    • Soil degradation
    • Erosion - water, wind, control
    • Soil acidification
    • Soil compaction
    • Chemical residues
    • Waste water treatment using reed beds
    • Suitable plants
  5. Types of Irrigation Systems
    • Gravity systems, pressurised systems
    • Sub surface systems, surface systems
    • Flood irrigation -border check, hillside, furrow
    • Pressurised systems - drip, sprinkler
    • Conventional systems - portable, semi permanent, permanent
    • Mechanised systems - travelling irrigators - soft hose, gard hose, boom types
    • Centre pivot irrigation systems
    • System components
    • Electric drive, hydraulic drive, water drive
    • Linear move systems, drive system
    • Fixed sprinkler systems -hand move, hose move, permanent
    • Quick coupling
    • Sprinkler heads - spray, rotating
    • Drive mechanisms - impact drive, gear, ball, cam, hex, cam gear drives
    • Design considerations
  6. Trickle Systems
    • Reasons to choose trickle
    • Do it yourself micro irrigation for amateurs
    • Time duration for watering
    • Automated systems
    • Microjet irrigation
    • Trickle system maintenance
    • Cleaning filters
    • Flushing
    • Using chlorine, doses, continuous chlorination
  7. Design Specifications
    • System components
    • Hydraulics - pressure
    • Measuring pressure - bourdon gauge, head of water
    • Calculating discharge or flow
    • Bernoulli's Equation
    • Velocity
    • Friction loss in systems
    • Water hammer
  8. Pumps and Filters
    • Types of pumps - piston, radial, mixed flow, axial flow
    • Pumps and pressure systems
    • Shallow well pumps, deep well pumps
    • Pumping mechanisms - piston, centrifugal, turbine
    • When a centrifugal pump fails
    • Preventing clogging in trickle irrigation
    • Controllers - automated, manual
  9. Selecting the Right System for a Plant
    • Water saving measures
    • Filtration
    • Flood, sprinkler, trickle irrigation
    • Case studies - putting greens, ornamental gardens, etc
  10. Design and Operation of Systems
    • Cyclic watering
    • Pulse watering
    • Irrigation schedules
    • Sprinkler spacing
    • Considering sprinkler performance in design
    • Electrical factors
    • Electric powered automatic systems
    • Design considerations


  • Explain the significance of soil in irrigation.
  • Explain how to determine when to irrigate in a small scale situation.
  • Manage irrigation in a given situation.
  • Explain the significance of different aspects of moving water including: drainage, pumps, filters, storage and recirculation.
  • Select an appropriate irrigation system for a given situation.
  • Explain the principles of design for a simple irrigation system.
  • Design a simple irrigation system.
  • Oversee the installation of an irrigation system.


Irrigation is the technique of supplying a plant’s needs for water. It is an integral part of successful crop production ranking as highly in terms of importance with fertilising and the control of weeds, pests and diseases. Its interrelationship with these other techniques can determine the outcome of the irrigation, whether beneficial or detrimental, depending on the skill with which it was undertaken. For example, irrigation may provide adequate water for successful crop production or it may provide too much. In the latter case, this could cause overloading of drainage systems or cause water tables to rise to the point whereby salts etc. are brought within reach of the plants’ root zones. Water may also make nutrients readily available or it may leach nutrients if applied excessively.


Water is essential to plant growth and is often the major limitation to productivity.  Irrigation is now playing a more important role in horticulture than ever before.  However, depending on the climate, the value of the plant, the value of the land and its suitability for irrigation, the cost, reliability and quality of the water supply, irrigation may or may not be possible or feasible.
Irrigation is most widely undertaken in arid and semi-arid climates where soils may be quite fertile, but natural rainfall is insufficient for plant requirements. It is also undertaken successfully in areas with other climate characteristics where it can be used to overcome water shortages in dry times, thus extending growing seasons and hence the types of crops that can be grown, or simply increasing the range of crops. It may also act as a safeguard against times of irregular or unreliable rainfall. Irrigation requirements may range from the complete supply of a plant's needs over the entire growing season down to the occasional small supplementary needs of plants in severe dry seasons. The use of irrigation to produce improved yields where plants can be grown with just natural rainfall is termed as supplemental irrigation.

Soil  Affects Irrigation Requirements

Soil Uniformity

The more uniform the irrigation block, the easier it will be to manage. Problems of patchiness can arise, for example, in hand forming when a cut is made into subsoil that is more clayey or more sandy than the topsoil. So, it is necessary to level the land and examine the soil to the depth of the maximum cut to determine the likely effect on soil texture.

Available soil water capacity

A high available soil water capacity is desirable for crops because the higher it is, the less likely the plant is to become stressed between irrigations. The best soils are generally loams or clay loams. The soil needs to be examined to the likely maximum rooting depth both to determine the available soil water capacity and to ensure there is no bedrock, hardpan or other root impeding layers.


This refers to process of water entry into the soil. It is influenced by:

a) Soil type and soil texture. Sandy soils generally have higher long term water penetration rates than clayey soils.

b) The condition of the surface soil. Water will enter faster if the soil surface is friable and open or is extensively and deeply cracked. Compacted or crusted soil with few cracks has a low infiltration rate.

c) The stability of the surface soil. Low water stability means that the soil crumbs do not stay together when wetted. Low water stability results in slow water penetration unless the soil is sandy. Also, it often results in the formation of a surface crust as the soil dries which will reduce infiltration at the next irrigation.

d) Depth of soil above an impermeable layer. The soil may consist of a light loam topsoil over a clay subsoil or bedrock. In this case, water up over the impermeable layer reduces water penetration.


This course is going to be of value to people working in:

  • Parks & gardens
  • Landscaping
  • Irrigation
  • Garden maintenance
  • Green keeping & turf care
  • Garden centres  




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