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Nitrogen is essential for plant growth being one of the main building blocks of proteins. It is important for biomass production and fruit production, maximizing photosynthetic assimilation leading to high strawberry yields
During periods of rapid growth, leaves that are short of nitrogen remain small and turn pale green or yellow. However, too much nitrogen can lead to an excessive leaf area which is out of balance with the rest of the plant, and also produces too many runners and insufficient flowers. Strawberries are quite sensitive to excessive rates of N and so nitrogen supply needs to be closely monitored and balanced with other nutrients. The total rate of N required will vary with variety and growing system.
Timing of N is also critical and programs need to be tailored to deliver enough leaf growth and strong fruit set without creating issues during fruit fill and at harvest. In field grown strawberries, this will mean focusing upon nitrogen applications in the fall and also early in the spring - to strengthen and build the plant and improve fruit production.
These N applications must be balanced with the expected release of N from any organic matter added to the soil in preparation for planting the strawberries.
Uptake figures confirm that around 3-3.5kg of nitrogen per ton of fruit is required.
Nitrogen uptake increases during the vegetative stage and reaches a peak just before the fruit starts maturing
Perennial systems can utilise N reserves held in the crown and roots, over the 2-3 years of production as a result of remobilisation in the spring. Thus, annual production systems commonly require and consequently receive higher N rates than perennial systems.
Relying on autumn applications only will not maximise production in spring. Spring nitrogen applications are essential to maximize yield, but they cannot compensate sufficiently if autumn application rates were too low.
When strawberries are grown in soil cultivation systems, split application of N is recommended for what is a relatively shallow-rooted crop, commonly grown on light, leaching prone soils. Nitrogen is better utilised when applied by fertigation compared to broadcast application (figures above).
A consistent low N rate applied by fertigation is much more effective than broadcasting N in one dose.
Phosphorus is only needed in relatively small quantities however deficiency at flower bud differentiation leads to reduced nuber of fruit buds and lower yields.
In field production systems phosphate is placed in the root zone before planting, but in substrate systems P is targeted at early development and fruit set.
Both potassium and magnesium are required for many plant processes so if either are limiting yield will be restriced
Applications of silicon help to boost yields with applications made from runner formation through to harvest, marginally more effective than those from flowering onwards.