Irrigation - Crops

Course CodeBHT304
Fee CodeS2
Duration (approx)100 hours
QualificationStatement of Attainment
This course teaches you more than just how to water a plant.
You will learn all about how water  can and should be managed, in order to optimise production of crop plants; whether vegetables, fruit trees, cut flowers, herbs or anything else.
It is all a matter of balance
Plant roots need an environment that contains both water and air. If the spaces between soil particles contain too much water it will push out the air, and that can create just as much of a problem, as what too little water does. If there is too much water, disease organisms can thrive; and roots may rot; and with too little water, plants can become sick and more susceptible to attack by pests and diseases.
Every type of plant needs to be treated differently when it comes to irrigation. When you grow different plants together, you may need to compromise and find a "happy balance".  When you grow a monoculture; irrigation may be simpler to manage -but there may be other disadvantages to growing that way.
Irrigation is common sense; once you understand what is going on with the plants, the soil and the water. This course allows you to build that understanding; so you can begin to make better decisions; use more effective practices; and ultimately be more productive when you grow crops.

Lesson Structure

There are 10 lessons in this course:

  1. Introduction
  2. Soil Characteristics And Problems
  3. Estimating Plant And Soil Requirements
  4. Drainage - drainage systems, dams, etc.
  5. Types Of Irrigation Systems
  6. Hydraulics - discharge and flow rates, etc
  7. Pumps And Filters
  8. Selecting The Right System For The Plant
  9. Trickle Irrigation
  10. Design And Operation Of Systems

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.


  • Identify and consult appropriate sources of information for the irrigation industry.
  • Explain the significance of soil characteristics to irrigation.
  • Determine when to irrigate in a small scale situation.
  • Explain the drainage aspect of handling water.
  • Explain the operation and selection of irrigation systems.
  • Explain the operation and selection of trickle irrigation systems.
  • Determine specifications for the design of an irrigation system.
  • Explain the pumps and filters needed for handling water adequately for crops.
  • Supervise the installation of an irrigation system.
  • Design and operate an irrigation system for crops.


If you irrigate properly, you will water thoroughly and infrequently. By making sure the water penetrates the soil properly and wets the total root zone each time, you will find each irrigation will have maximum benefit and the soil will take longer to dry out (reducing the frequency of irrigations required). The amount of water applied and the period between irrigations will need to be adjusted continually to take into account changing weather conditions; and changing soil conditions (where soils are being worked on). The amount of water applied can be restricted by supply. This is increasingly a problem in heavily populated areas where the population growth is outstripping the increases in water storage areas.

Deep rooted plants (turf, trees or shrubs) are able to pull up water from deeper in the soil than shallow rooted plants. If these plants are watered in a way that the water penetrates deeper, there will be a supply of water deep in the soil which is insulated from the surface by the soil above. This water will remain in the soil accessible to the plant for a long time, where as water near the surface will have dried out from the affect of the sun or wind over the soil surface.
How Often Should Plants Be Watered?
It all depends upon the type of plant being watered; the environment and the soil conditions.
Water will infiltrate into the soil at different rates in different soils. Moisture will evaporate more in windy conditions an/or in warmer conditions. Water can also be lost through plant foliage; or stopped from reaching the soil by plant foliage.  
There are a lot of factors that interact to affect irrigation; and this course is designed to help you better appreciate the factors and the interactions.
The zone between wilting point and field capacity is important in irrigation, with the aim being to keep moisture levels within this zone. It has been found generally that plants take most of their requirements from the upper half of the root zone and as a consequence only about half of the available water is used. Irrigation is therefore generally required when approximately half of the available water is used up. The amount of water to be applied to a crop is therefore half of the available water in the root zone of the crop when the soil is at field capacity.  
Irrigation applications are timed according to how quickly the plants use the available moisture, and are generally dependant on climatic conditions and the availability of nutrients. The rate at which water is supplied by irrigation is also important and is governed by soil infiltration rates (the rate at which water will pass into the soil). If water is supplied at a rate greater than the ground can absorb it, then runoff may occur and water may be wasted and lost to the plants. The following table gives an indication of infiltration rates for some soils.
The ideal situation is where application rates are equal to infiltration rates. Infiltration rates can also be affected greatly by compaction which causes reduction in pore space and hence space available for water and its passage. 
Compaction becomes very important when designing irrigation systems for areas that are likely to suffer from a lot of traffic such as bowling greens, golf tees and popular lawn areas. Compacted soils are likely to have infiltration rates as low as 5 10 mm/hr. Measures that may have an effect on increasing infiltration rates such as coring of bowling greens should also be considered when irrigating, and application rates should be adjusted accordingly


People working on vegetable farms, orchards, herb farms, cut-flower farms and any other horticultural enterprise requiring irrigation.





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