Irrigation management

Irrigation allows you to:

• grow more pastures and crops
• have more flexibility in your systems and operations
• produce higher quality crops/pastures as water stress can dramatically impact on the quality of farm produce
• lengthen the growing season (or start the season at an earlier time)
• have 'insurance' against seasonal variability and drought
• stock more animals per hectare and practice tighter grazing management due to the reliability of pasture supply throughout the season
• maximise benefits of fertiliser applications
• use areas that would otherwise be less productive
• take advantage of market incentives for unseasonal production
• have less reliance on supplementary feeding (grain, hay) in grazing operations due to the more consistent supply and quality of pastures grown under irrigation
• improve the capital value of their property
• cost save or get greater returns.

Choosing an irrigation system

Deciding which irrigation systems is best for your operation requires a knowledge of:

• equipment
• system design
• plant species
• growth stage
• root structure
• soil composition
• land formation.

Irrigation systems should encourage plant growth while minimising:

• salt imbalances
• leaf burns
• soil erosion
• water loss.

Types of irrigation

Furrow systems

This system comprises a series of small, shallow channels used to guide water down a slope across a paddock. Furrows are generally straight, but may also be curved to follow the contour of the land, especially on steeply sloping land.

Row crops are typically grown on the ridge or bed between the furrows, spaced from 1 metre apart.

Flood or border check systems

These systems divide the paddock into bays, separated by parallel ridges or border checks. Water flows down the paddock's slope as a sheet guided by ridges. On steeply sloping lands, ridges are more closely spaced and may be curved to follow the contour of the land.

Border systems are suited to orchards and vineyards, and for pastures and grain crops.

Level basin systems

These systems differ from traditional border check or flood systems in that slope of the land is level and area's ends are closed.

Water is applied at high volumes to achieve an even, rapid ponding of the desired application depth within basins.

Center-pivot sprinkler systems

A center-pivot sprinkler is a self-propelled system in which a single pipeline supported by a row of mobile towers is suspended 2 to 4 metres above ground.

Water is pumped into the central pipe. As the towers rotate slowly around the pivot point, a large circular area is irrigated.

Sprinkler nozzles mounted on —  or suspended from —  the pipeline distribute water under pressure as the pipeline rotates.

The nozzles are graduated small to large so that the faster moving outer circle receives the same amount of water as the slower moving inside.

Hand move sprinkler systems

Hand move sprinkler systems are a series of lightweight pipeline sections that are moved manually for successive irrigations.

Lateral pipelines are connected to a mainline, which may be portable or buried.

Hand move systems are often used for small, irregular areas.

Hand move systems are not suited to tall-growing field crops due to difficulty in repositioning laterals.

Labor requirements are higher than for all other sprinklers.

Solid set and fixed sprinkler systems

Solid set or fixed refer to a stationary sprinkler system.

Water-supply pipelines are generally fixed (usually below the soil surface) and sprinkler nozzles are elevated above the surface.

Solid-set systems are commonly used in orchards and vineyards for frost protection and crop cooling.

Solid-set systems are also widely used on turf and in landscaping.

Travelling gun sprinkler systems

Travelling gun systems use a large sprinkler mounted on a wheel or trailer, fed by a flexible rubber hose.

The sprinkler is self-propelled while applying water — travelling in a lane guided by a cable.

The system requires high operating pressures, 100psi is not uncommon.

Side-roll wheel-move systems

Side-roll wheel-move systems have large-diameter wheels mounted on a pipeline. This enables the line to be rolled as a unit to successive positions across the field.

Crop type is an important consideration for this system since the pipeline is roughly 1 metre above the ground.

Linear or lateral-move systems

Linear or lateral-move systems are similar to center-pivot systems, except that the lateral line and towers move in a continuous straight path across a rectangular field.

Water may be supplied by a flexible hose or pressurised from a concrete-lined ditch along the field's edge.

Low-flow irrigation systems (including drip and trickle)

Low-flow irrigation systems (including drip and trickle) use small-diameter tubes placed above or below the soil's surface. Frequent, slow applications of water are applied to the soil through small holes or emitters. The emitters are supplied by a network of main, sub-main and lateral lines.

Water is dispensed directly to the root zone, avoiding runoff or deep percolation and minimising evaporation.

These systems are generally used in orchards, vineyards, or high-valued vegetable crops.

Source of irrigation water

The vast majority of irrigation water use is pumped directly from a water source — river, creek, channel, drag-line, hole, dam or bore.

Irrigation scheduling

Irrigation scheduling is the process by which an irrigator determines the timing and quantity of water to be applied to the crop or pasture. The challenge is to estimate crop water requirements for different growth stages and climatic conditions.

To avoid over or under watering, it is important to know how much water is available to the plant, and how efficiently the plant can use it. The methods available to measure this include:

• plant observation
• feel and appearance of the soil
• soil moisture monitoring devices
• available water from weather data.

Over or under watering problems

While irrigation has provided a number of important benefits there can be potential drawbacks of over or under watering.

Under-watering can cause:

• loss in market value through yield reduction
• reduction in fruit size and quality.

Over-watering can cause:

• unwanted vegetative growth
• losses of valuable water to the water-table
• erosion
• pesticides, pathogens and weeds to spread during irrigation
• runoff
• increased operational costs (labour, pumping, cost of water)
• leaching of nutrients
• downgraded product quality and reduced yield
• higher operational costs for the producer
• pressure on water resources.