Drip irrigation is the most effective means of supplying water to the strawberry crop, (Figure 23). In this trial, making best use of water, delivered yield responses over surface irrigation of over 20%. Adding fertilizers to the drip irrigation water is a major advantage over broadcasting fertilizer and irrigating separately. Yield responses of around 40% have been shown (Figure 24), through better utilization of the nutrients that are applied.
Application Strategies
Pre-planting
Pre-planting soil preparation provides an ideal opportunity to apply base fertilizers. Direct contact between newly planted runners and soil applied fertilizers can damage roots and compromise crop establishment prior to the winter. As a result, fertilizers should be thoroughly incorporated into the soil before the positioning of the straw or plastic mulch. Fertilizers can be applied during bed formation and should be placed in a band 5-10cm below the surface and in between the intended planting rows.
Post Planting
Broadcasting of fertilizer can be practiced in systems where straw has been used as mulch, but is not practical with strawberries under plastic.
Fertilizer placed in planting holes can damage the plants leading to toxicity issues. To avoid this potential for toxicity, some growers will cut a hole in the plastic 10 to 15cm from the crown of the strawberry and place the fertilizer in this hole. Fertilizers applied along walkways close to beds are often ineffective and can lead to run-off. For this reason, fertigation is most commonly recommended for in-season fertilizer application.
Fertigation
Fertigation, by providing nutrients through the irrigation system located under a plastic mulch or in table top systems, delivers fertilizer direct to the plant to meet an immediate need. This allows the application of soluble fertilizers to the plants throughout the growing season and at the same time maintains a good water balance for the crop.
When fertigating strawberries grown in soil, it is important to keep the soil moisture level at or near field capacity and to maximize the area of the wetted bulb. This helps to avoid high concentrations of fertilizer salts close to the root zone, which can occur if the soil is allowed to dry out (see Soil Requirements).
Avoiding the use of water with high (bi-) carbonate levels will help reduce the risk of phosphate, sulfate or calcium rich fertilizers from precipitating out and blocking the drippers. If the irrigation water contains high (bi-) carbonate levels, acid should be used to neutralize the solution.
It is also common practice to irrigate before and after injecting the fertilizer. This helps move the nutrients down into the root zone, avoids the build-up of fertilizer salts in the drip system and / or pockets of fertilizer salt concentrations within the soil.
Under table-top systems, fertigation is through a continuous flow of water and nutrients in this closed system can be much more closely regulated. See section on hydroponics and substrate systems on page 15.
Foliar Application
Foliar application is used to address an immediate nutritional need. It applies the nutrient directly to the plant and relies on leaf and fruit absorption. In in-field cultivation systems foliar sprays are used when soil applications are ineffective and when plants are under stress during early fruit set and development.