Irrigation and fertilisation have a major influence on the performance of a plant at blueberries. The quantity and quality of the water used has a fundamental effect on the health and performance of a plant, which must also be fed correctly in order to produce in an optimal and balanced way.
In this exclusive interview Andrea Pergher, Fall Creek's technical manager, introduces us to the general criteria and best practices for properly watering and feeding plants at blueberry.
What is the role of irrigation in the growth of the blueberry plant?
The management of water supply must first be adapted to the age of the plant. In a small plant the amount of water needed is different than in a large plant: particularly in the first year it is not necessary to give too much water. In the first year it is advisable to leave the plant almost dry in order to stimulate the new roots and gradually increase the root system. For adult plants in full production, it is necessary to take into account evapotranspiration, which is determined by temperature, wind and phenological state, and therefore interventions will vary between April and June.
How do irrigation interventions vary over the season?
In the early phenological stage of blueberry Northern Highbush, i.e. in April, watering will not be abundant because the plant without leaf mass does not absorb water. The peak of water use will be in May and June. In May the green fruit will swell, the length of the day will increase and the leaf area will increase. A lack of water during this period can be fatal for the plant. June is the peak of water demand during ripening and fruit enlargement.
What other factors influence irrigation?
Irrigation must be carried out taking into account a variety of parameters. That is, it is not necessary to consider only the time of irrigation. For example, for soil irrigation, the type of soil must be evaluated to determine the total amount of water and the interval between irrigations. For example, a sandy soil will require more frequent and shorter irrigation, whereas a clay soil will require less frequent and longer irrigation.
In concrete terms, how do you determine the correct amount of water needed for a specific installation at blueberries?
It is necessary to calibrate the water supply precisely, as blueberry is afraid of water stagnation, which causes root rot and consequent damage to the plant. In order to determine how to irrigate, it is necessary to determine the field capacity. This is done by cutting a section of soil on the row transverse to the plant and the irrigation system; a depth of 30 cm and a width corresponding to the row is sufficient, exposing the root system. At this point, the irrigation system must be opened and it is necessary to see how long it takes for the soil to soak and drain below 30 cm, which is the normal depth to which the root system of blueberry reaches. It is also necessary to assess how long it takes for the soil to dry out and when the plant starts to drop the apical parts of the leaf.
Which irrigation methods should be used for potted crops?
With regard to irrigation in pots, the amount of water required is measured by drainage: at the end of the day 20-30% of the water used must be drained, i.e. this amount must be present in the saucer. For full systems, drainage of more than 30% indicates over-watering, whereas drainage of less than 30% indicates under-watering. These parameters apply to established plants, whereas for young plants irrigation should be limited to encourage root development.
Regarding the nutrition of the blueberry plant, what are the main tips?
Before we move on to talk about plant nutrition, we need to take into account the chemical aspects of irrigation, which can also have an effect on plant nutrition. The actions taken to give the irrigation water the right acidity also have a fertilising effect that must be taken into account to keep the plant in the right balance.
What are these interactions between irrigation and nutrition?
For blueberry it is necessary to acidify the water according to the bicarbonates it naturally contains. Depending on the characteristics of the water and the phenological period, sulphuric acid, nitric acid or phosphoric acid can be used. In addition to the acidifying effect, these elements also have a nutritional effect, and therefore it is necessary to dose the interventions well; for example, at the beginning of the season it is advisable to use nitric acid to push the plant, while from mid-season it is advisable to switch to sulphuric acid for a more balanced action. In the case of calcareous water (1-2 millimoles), phosphoric acid is recommended all year round. But with 4-5 millimoles, phosphoric acid will not be used all the time in order to avoid an excess of phosphorus that can unbalance the plant.
Turning to nutrition, how are fertilisation measures structured?
Feeding will take place from April to July and then gradually decrease until it stops in September. From May it is advisable to use nitrogen in ammoniacal form (NH4), starting to reduce the doses from July and ending in August. From September, when the plant is not growing, it is important not to carry out nutrition treatments in order to allow flower differentiation, which otherwise does not take place.
What fertilisers are recommended?
Acid-reacting fertilisers are recommended to help keep the pH low, e.g. sulphate fertilisers. If the pH of the soil is right, i.e. between 4.5 and 5.5, it is advisable not to overdo the use of trace elements.
Is there a simple indicator to monitor the health of the plant?
An important indicator of the health of the plant is the colour of the leaf: yellowing of the leaf normally indicates an incorrect pH of the soil, substrate or water and this in turn causes an unbalanced uptake of elements.
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