Irrigation Management (Horticultural)

Develop Your Irrigation Skills & Knowledge

Work towards becoming an irrigation specialist This advanced course assumes some knowledge of irrigation equipment and installation. It is suitable for foremen, supervisors, managers and installers of irrigation systems.

It includes topics such as how to monitor water usage, measuring volumes of water administered, problems with different impurities in water, electronic equipment, and different types of system design and components. 

Towards better management, design and irrigation system maintenance  

This course is a natural progression from Irrigation (Gardens). It can be studied as a stand alone course; however we would normally advise to undertake Irrigation Gardens first.

The following topic areas are covered:

• Ways to optimise water efficiency
• Scheduling irrigation for nurseries, gardens, turf and horticultural crops.
• Drainage system design
• Operating irrigation controllers
• Managing system maintenance
• Managing fertigation
• Evaluating irrigation designs
• Design of different systems

This course builds on skills achieved in Irrigation (BHT210 and BHT204) modules to develop students’ skills to manage the design and operation of large scale irrigation systems for horticultural applications.

Lesson Structure

There are 8 lessons in this course:

1. Wastewater and Recycling
   • Introduction
   • Humans & Water
   • Water And Plant Growth
   • Minimising Plant Requirements
   • Xeriscaping
   • Wastewater
   • Types Of Water Wastage
   • Evaporation
   • Seepage
   • Runoff
   • Overspray
   • Scheduling
   • Recycling Wastewater
   • Wastewater Treatment (Reed-Beds)
   • Suitable Plants
2. Measuring Water Usage
   • Climate
   • The Hydrological Cycle
   • Infiltration
   • Rainfall
   • Temperature
   • Wind
   • Microclimates
   • Special Applications
   • Measuring Soil Moisture
   • Water Monitoring Equipment
   • Measuring Water Usage
3. Drainage
   • Introduction
   • Drainage
   • Rainfall
   • Improving Permeability During Construction
   • Cultivation
   • Adding Soil Ameliorants
   • Chemical Treatments
   • Improving Surface Drainage After Construction
   • Sand Slitting
   • Aerating
   • Sub Soiling
   • Layout Of Drains
   • Herringbone
   • Grid
   • Outlet
   • Gradients
   • Distance Between Drainage Pipes
   • Depth Of Drains
   • Types Of Drains
   • Clay Pipes
   • Corrugated Plastic
   • Fibreglass Strip Drain
   • PVC Pipe
   • Laying The Drain
   • Contingencies To Deal with Flood
4. Irrigation Controllers
   • Introduction
   • Irrigation Controllers
   • Controllers
   • Automatic Controllers
   • Time Clocks
   • Computerised Tap Controllers
   • Manual Controllers
   • Battery Powered Solenoid Valves
   • Water Volumes and Duration
   • Pumps And Pressure Systems
   • Pump Flow
   • Pressure
   • Types Of Pumps
   • Shallow Well Pumps
   • Deep Well Pumps
   • Pumping Mechanisms
   • Piston Pumps
   • Centrifugal Pumps
   • Turbine Pumps
   • When Centrifugal Pump Fails to Operate
5. System Maintenance
   • Maintenance Of Watering Systems
   • Maintenance Procedures and Scheduling
   • Maintaining Trickle Irrigation Systems
   • Maintaining Water Quality
   • How To Improve the Quality of Water from Any Source
   • Problems Of Water Quality and Their Remedies
   • Physical Impurities
   • Chemical Impurities
   • Biological Impurities
   • Bacteriological Impurities
6. Fertigation
   • Introduction
   • Advantages of Fertigation
   • Disadvantages of Fertigation
   • Fertigation Types
   • Proportional Application
   • Quantitative Application
   • Continuous Application
   • Three Stage Application
   • Fertiliser Injectors
   • Pump Injectors
   • Pressure Differential Injectors
   • Suction Injectors
   • Fertiliser Applications
   • Plant Nursery Fertiliser Injection Techniques
7. Design Evaluation
   • Design Considerations
   • Importance of Design
   • Surface/Flood Irrigation
   • Sprinkler Irrigation
   • Trickle Irrigation
   • Microjet Irrigation
   • Do It Yourself Micro Irrigation Systems
   • Time Length of Watering
   • Automatic Systems
   • Water Management in Turf
8. System Design
   • Pre-Planning Information
   • What Is the Soil Like?
   • Record The Dimensions and Other Measurements
   • Consult The Local Council on Relevant By Laws
   • Study The Environment of The Locality
   • What Resources Are Available to Do the Job?
   • What Preferences and Priorities Does the Client or Owner Have?
   • Type of System
   • Underground Pipes
   • Drainage

Each lesson culminates in an assignment which is submitted to the school, marked by the school's tutors and returned to you with any relevant suggestions, comments, and if necessary, extra reading.

What You Will Do

• Contact your regional or local water authority.
  • Ask them for information on their water restriction policy.
  • When are water restrictions enforced and how do they affect water users?
  • Focus mainly on the problems experienced by agricultural users.
  • Consider ways that users can minimise their dependence on water access?
  • Write a brief report on your findings and submit with your assignment.
• Visit a property that uses irrigation.
  • Discuss with the manager the methods that are used to decide when to water and how much water to use.
  • Is irrigation an important element in the success or otherwise of the property?
• Choose a drainage system to which you can get access.
  • Remember a drainage system is designed to cope with most situations.
  • They are many examples in your local everyday environment.
  • Some examples might include the guttering on your house or even on your car.
  • Discuss how the system operates and include sketches to show design features.
• Contact a number of companies that offer computerised and technology solutions to irrigation.
  • Obtain prices and information if possible on appropriate working installations of their product.
  • If possible try a follow up visit at least one (1) operation and discuss the product with a user as well as a retailer. If distance or transport is a problem then you could try writing for this information, which would be suitable for the purpose of this set task.
• Visit a property that uses large irrigation systems.
  • Enquire about the maintenance of their systems.
  • Consider how is water quality monitored and maintained?
  • Investigate at least two irrigation supply companies.
  • Observe how they service customers.
  • Consider: are there any other services they provide?

Learn to Understand Soil Moisture?

Moisture is present in the soil and can be described through a range of hydraulic terms. These terms include things like field capacity, wilting point, etc.

The type of soil that exists, and the components of that soil greatly influence the moisture levels. Clay soils with small particles are known to hold more water than sandy soils. Soils high in organic matter will hold more water than non-organic matter soils.

Too much water however in the soil may result is plant decline, even death, due to the lack of oxygen present. It is crucial a balance is made between water and air so that the plants will grow. Some plants required more water bogged soils whereas others need extremely well drained soils.

After irrigation or rainfall, water causes saturation of the soil's surface. As a result of gravity, the water will make its way down the soil profile by gravity and capillarity filling most (or all) air pores with water. As more water is added, the depth of saturation increases. In some cases, hydrophobic reactions on the soil surface will prevent water from being absorbed into the soil profile.
 
In time, water will percolate down through the profile (i.e. drain through). Soil will hold onto some of this water as a result of surface tension. As this water is held by tension, it takes suction force form the plant to extract the necessary water needed: a small farce will extract water from large pores; a large force will extract water from small pores which hold with greater pressure.

Soil texture and structure greatly influence the holding ability of the soils. Textures of clays have a greater holding ability than sands. Structure (the arrangement of soil particles and aggregates) influences the capillary system which in turn affects the drainage, water holding ability, aeration and erosion properties.
 
Sand, due to its large texture, does hold much water. However, it makes the water readily available to plant roots. Clay, with its small particle size, has a good tension force and therefore holds onto water well and does not release water as easily. Loam soils are regarded as the best type due to their ability to exhibit characteristics of both.

In order for correct irrigation practises to be implemented, a measurement of soil moisture content is required. The object of irrigating a crop is to provide as close to optimal growing conditions as is possible. Too much water can be just as detrimental to a crop as too little water. The soil surface may be dry, yet the moisture content of the soil in the root zone may be perfect. The leaves of the plant can be used as an indicator of the adequacy of available water.

Briefly, the leaf cells through osmotic action (i.e. transpiration) cause water to be drawn up through the roots and hence out of the surrounding soil. This decreases the water content and increases the suction potential in the soil which can be measured with a tensiometer. As water content drops further the plants leaves will begin to wilt due to loss of turgidity.

The ‘permanent wilting point’ of a plant indicates at what stage of water deprivation the plant will not recover from wilting. This should be avoided at all costs as it is at this point that the plant will have suffered too much damage and very likely the crop will fail. In order to assess the soil condition a number of tests and methods of empirically measuring soil moisture characteristics have been developed.

Water Monitoring

In the past, much of the equipment available lacked accuracy and real value in industry. Nowadays, this situation has largely changed, although the accuracy of some less expensive devices may still be questionable.

Some of the devices now available include:

a) Gypsum Blocks
This is an older method, used for monitoring, but not controlling moisture levels.

b) Neutron Probe Meters
This is an older technique, relatively expensive (compared with newer devices), and used less often today than in the 1970's and 80's. It is used for measuring only.
 
c) Tensiometers
A tensiometer measures the soil moisture suction characteristics of soil (i.e. how tightly water is held on the surface of soil particles).

A tensiometer is a long impermeable cylinder (the probe), tipped with a porous material at the base which water in the soil can exert pressure on, as it is absorbed into the water filled probe. The top of the tube is fitted with a gauge to measure changes in pressure inside the cylinder/probe.

In the past, they have been used by farmers and growers to give on-the-spot field measurements. These are measured in ‘bars’ with a range of 0 bars signifying excellent available water characteristics to 0.8 bars signifying poor available water characteristics. These figures are subject to soil type variations with clay soils having very different implications to say, loams and sands.

An example of tensiometer use is by the vine furrow irrigators of the Victorian Mallee district of Australia. They are encouraged to irrigate when their tensiometer readings are between 30-40 centibars (0.3 - 0.4 bars) during the early months of the season (pre-January). The lesser tension figure relates to a sandy soil and the higher figure to a silty clay loam.

Tensiometers are used less today than in the past, due to the range of other technologically advanced devices now available.

d) Ceramic Block Sensors
Sensors are buried in, or near, the root zone of plants. Electrical characteristics of these sensors will respond to water levels in the surrounding soil triggering irrigation to start at a pre-set level, and to switch off at another level. Soil salinity does not affect the device. Irrigation efficiency typically results in a 50% decrease in water usage. An example is the Cumming Watermatic Irrigation Management System.

e) Heat Sensor System
Buried sensors give off heat pulses and measure the response which varies according to moisture content of the soil.  An example is the DRW Micro Link.

f) Dielectric Scanning Device
Probes are placed inside PVC tubes sunk into the soil. These probes measure the dielectric constant of the soil at routine intervals - commonly every 10-60 minutes. An example is the EnviroSCAN Water Monitoring System which can be powered by batteries or solar panels. It is precise and flexible.

Applications
Any irrigation measuring or controlling device is only as good as the way in which it is used. Measurements must be taken in the root zone of the plant for them to be appropriate. The irrigator must also have the ability to interpret the meaning of measurements of soil moisture and relate the measurements to the needs of a particular type of plant being grown. 

WHY STUDY THIS COURSE?

This course assumes that students have a basic understanding of irrigation systems and components. If not, it is advisable to take Irrigation (Gardens) or one of the other introductory irrigation courses first.  This course guides students in the design and implementation of irrigation systems to meet a wide variety of purposes from orchards to crops, and sports fields to private gardens. Graduates will be able to calculate water usage and requirements, and assess the viability of irrigation systems. The course is aimed at those seeking higher levels of responsibility in irrigation.

This course is relevant to people working in:

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