Irrigation and fertiliser practice
The following guidelines are based on research conducted in Wanneroo over many years. With good fertiliser and irrigation practices, and depending on variety, strawberries can consistently produce up to 1.5 kilograms of fruit per plant each season.
The industry average is closer to 0.50–0.75kg but one kilogram should easily be achievable by following recommended guidelines.
Irrigation systems
Overhead sprinklers are used for establishment and for cooling plants in hot weather. Drip irrigation is recommended throughout the season.
Drip irrigation is more efficient, as it uses less water and applies it more evenly. Fruit is kept dry, lowering disease incidence.
Overhead irrigation for establishment
Overhead irrigation should be applied to prevent new runners from wilting. When plants arrive they have no active roots. Reducing plant stress (wilting) will promote quicker root establishment and the take up of nutrients, enabling good plant growth.
The frequency and duration of overhead irrigation will depend on weather and the condition of the runners at planting. Compact runners with smaller leaves require less irrigation as they have less leaf area than long large-leafed runners that lose water more readily.
Many growers use ‘leaf-off’ plants. These generally arrive about two weeks later than leaf-on plants and have experienced a larger degree of chilling. They are less fragile than leaf-on plants but still require some overhead cooling.
When planting in February or early March, cooling may be required between once and four times an hour during the heat of the day until roots are established and drip irrigation is effective.
Growers can use a significant proportion of their water allocation during this period. As the goal is cooling rather than irrigation, using a low output nozzle with a finer droplet size may reduce water use.
Good irrigation uniformity and cooling can be achieved by using smaller nozzles at the right pressure. Twin-nozzle sprinklers may use up to 1000 litres per hour whereas some newer low-flow sprinklers may only need 500L to achieve the desired result.
Drip irrigation should be used in addition to overhead irrigation during establishment to promote root establishment and prevent soils from drying out between planting holes.
Sands in Western Australia can become water repellent or non-wetting if soil moisture is not maintained and are almost impossible to re-wet using drip irrigation. Even in uniformly wet sandy soils, the lateral spread of water is no better than about 15–18cm. When sandy soils dry out, water follows preferred pathways and even that limited spread may not be achieved.
Other factors can have major effects on the penetration of overhead irrigation and rain, such as:
- the size and shape of the planting hole punched in the plastic
- the evenness of the bed surface, and
- how tightly the plastic has been laid.
Drip irrigation
The most common configuration for commercial strawberries on sand is two lines of drip irrigation per four-row bed with each line laid between the two outer rows of plants.
However, growers use a range of planting and irrigation configurations including two, three and four-row beds using one, two or even three rows of drip tape. Some growers plant two ‘pairs’ of rows with plants offset rather than four rows equally spaced across the bed.
Bury the lines slightly so they stay in place and don’t move around. This gives the best chance of all plants receiving the same amount of water and fertiliser.
A 25cm dripper spacing is common but a closer spacing, if scheduled effectively, will lead to more even irrigation and may give better yields and quality.
Dye tests and irrigation monitoring in the Wanneroo area have shown that increased volumes (longer duration) will not increase the spread of water beyond about 15–18cm total or 7.5–9cm on either side of the dripper. This indicates that 15 to 20cm distance between drippers would deliver irrigation more evenly to the crop than 25cm.
Experience in Wanneroo including dye testing showed that a yield advantage was achieved with a 10cm dripper spacing but that may not be practical for many growers.
Longer run times only waste water (and fertiliser) by sending it deeper into the soil profile, past the root zone.
Questions exist as to what degree plant roots will grow towards soil water and what detriment, if any, this may have on yields. In Florida, soils are also sandy but have a higher proportion of finer silt particles, so lateral water movement is better. Beds are constructed 30cm higher than the pathways and growers aim to promote extensive root growth to fill the bed as a matter of priority after planting, to maximise nutrient uptake and efficiency.