Over-irrigating wastes precious water, energy and money and can lead to leaching or run-off of nutrients that can pollute groundwater, rivers and estuaries.
Under-irrigation results in poor production and high costs per unit of product.
The goal is to achieve efficient water use and time spent planning and designing your irrigation system will be an investment in the future of your crop.
Apart from water being essential for plant survival, it is also the mechanism for root systems to access fertilisers and trace elements in the soil.
At the crop-level irrigation can be significant in three key areas:
- Increased production — where seasonal rainfall is inadequate, irrigation delivers the moisture and nutrients the plant needs to develop optimal crop levels.
- Frost control — overhead sprinklers are sometimes used to minimise damage in frost-sensitive crops. The sprinklers can be manually operated or set to start automatically when the temperature falls to a pre-determined level on still nights.
- Heat reduction — evaporation from overhead sprinklers will reduce stress in some crops that might be adversely affected by extreme heat.
Consider soil types
Soil characteristics will influence the type and timing of your irrigation program.
Moisture will drain towards the root zone and plant utilisation and water use efficiency will depend on how long it is held there. The ideal soil will have sufficient organic matter to hold moisture and be coarse enough not to become waterlogged.
The two soil type extremes are coastal sand and heavy clay:
- sandy soil — lacking in organic matter, sandy soil allows the water and nutrients to leach down and out of the root zone. Short irrigations applied more often will keep the root zone wet for longer.
- clay soil — heavy clay soils are fine textured and may not have enough drainage capacity for good root development. If too much water is applied too often, waterlogged soil can result. Longer intervals between irrigations will help with drainage.
The irrigation system you select will be determined by the crop you grow, the topography and the efficiency of the system.
The following are common types of irrigation systems:
- Flood irrigation is the least efficient option and is only used on laser-levelled pasture blocks. Flooded furrow irrigation is often used in large scale row crops.
- The centre pivot, travelling and fixed overhead sprinklers, are suited to pasture and annual horticultural crops on flat land.
- Micro sprinklers are a good option in tree crops. Compared to larger sprinklers they are efficient, saving water by only watering the ground under the trees and not the inter-row space. They work at lower pressure and are cheap to run.
- Trickle and drippers are efficient, economical systems used in annual row crops, orchards, vineyards and floriculture. Both are well suited to water efficient domestic and ornamental gardens.
- Subsurface drip irrigation delivers the water directly to the root zone eliminating evaporation loss and is commonly used in annual vegetable and floriculture crops where good quality water is available. Subsurface systems can be expensive when used over a large area and periodical line flushing is required to keep the lines open.