IRRIGATION - CROPS

Learn to make more efficient use of on farm water resources.

From a cropping perspective, irrigation is important in ensuring that crop plants have sufficient water to adequately perform functions such as respiration and evapotranspiration, and to actively produce harvestable material.

Water is a limiting factor for both quality and quantity of yield in many crop plants.

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

Aims

• Identify and consult appropriate sources of information for the irrigation industry.
• Explain the significance of soil characteristics for 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.

Gain a better understanding of how to manage the water needs for any horticultural crop

Water is a major component of all plant growth. In succulent, leafy plant material the water content may be as high as 85 - 95%. Of all materials taken in by a plant, water is absorbed in the largest quantities. Generally, less than 5% of the water taken in by the plant is retained for use within the plant. In some cases, the amount used is as little as 1%. The water remaining in the plant is used mainly:

• In the cell tissues which are 75 - 90% water
• As a carrier of foods and growth regulators from the leaves via the transport system (vascular system)
• In very small quantities, as part of the photosynthetic process.

The remaining 95% or more acts as a carrier of nutrients up through the plant. Once it has carried the nutrients up it becomes surplus and is disposed of to the atmosphere through the leaf stomata (leaf pores). This loss of water also helps to keep the leaf canopy cool reducing the likelihood of leaf burning or desiccation. This upward movement of water from the roots through the stems via the vascular system to the leaves is sometimes known as the transpiration stream.

Transpiration is the principle method of water movement into and through the plant. This is a physical process powered by the evaporation of water as a vapour into the atmosphere from the plant leaf. This water is lost from the outer surface of the leaf mesophyll cells (the spongy interior of the leaf). As the water is lost the cells become dehydrated. This creates a potential difference between the dry mesophyll cells and adjacent moist ones. Because of waters strong cohesive property (strong resistance of water molecules to be pulled apart) water from the adjacent moist cells diffuses through the cell walls into the dehydrated cells thereby relieving the pressure differential. The continued loss of water molecules from the leaves by evaporation creates a continual flow of water throughout the plant. This results in the pulling of replacement water from the soil via the roots and up the plant stem into the leaf.

When there is adequate water in the soil and conditions are favourable for evaporation at the leaf surface, then water moves easily into the roots from the soil and up into the plant via the xylem. As the soil dries, the water remaining in the soil is held more tightly to the soil particles. If evaporation through the leaf continues then there is insufficient water to replace that lost through evaporation. Water stress then occurs in the plant and wilting may also occur. In severe cases, wilting may be permanent - resulting in permanent damage to the plant or even death.

In times of water shortage, the leaf stomata may only open late at night or early in the morning when humidity is high or dew is present. If water stress continues for a prolonged period then the stomata may only open for short periods to allow the discharge of waste gases (e.g. oxygen) and to take in carbon dioxide. There will be little growth at these times.

Too much water in the soil can also be a problem for healthy plant growth. While some plants are adapted to growing in waterlogged soils, or directly in water, the majority require sufficient levels of oxygen in the root zone to maintain healthy growth. If a soil is poorly drained or becomes flooded in some way then the water will displace all air in the soil leaving insufficient oxygen for the plant roots to metabolize the carbohydrates they require for energy and growth. The root tissue will die leaving no way for water to move from the soil to the upper parts of the plant, which will subsequently wilt from a lack of water.

• Improve your practices on a market garden, orchard, plant nursery or farm
• Improve your career or business prospects
• Work in irrigation services or supply
• Advise others on better water conservation and management

Who should study this course?

Those who are growing any Agricultural or Horticultural crops, working in the industry, or planning a commercial enterprise. This course gives students a very sound grounding in understanding the fundamentals of efficient irrigation. Students will be taught about the different types of irrigation, filtering methods and the use of appropriate pumps.