Fertigating blueberries requires greater precision given the particular demands of this crop.
The combination of relatively high nutritional demands, its low tolerance to salinity and the plant’s shallow roots calls for continued dosing in order to meet its fertilisation needs without saturating the soil with salts.
We can achieve this by spreading the fertilisation over as much time as possible: the greater the volume of water containing the nutrients, the lower the salinity. Therefore, every time we irrigate should be seen as an opportunity to fertigate, reducing the amount of fertiliser-less water the plant receives to a minimum.
When the salt content of our soil is high, whether we have found this out from a soil analysis or from the characteristics of the original water, we can perform a pre-irrigation with no fertilisers in order to wash the salt away.
Once we have decided on the fertigation strategy we are going to employ, controlling the application is key to ensuring that our expected formula is accurately reproduced in the irrigation solution.
Time dosing using precise flow rate dosing systems means that we have to calculate the volume for each sector in proportion to the programmed irrigation time. In this system, batches of water are created both with and without fertiliser for each irrigation operation, which increases the salinity of the batch that contains the nutrients and makes it less accessible to the crop. This issue can be resolved by dosing in proportion to the instantaneous flow and controlling the electrical conductivity.
Dosing in proportion to the instantaneous flow, measured using a high-frequency flow meter, guarantees that the exact concentration required of each of the nutrients is achieved.
Devices such as the ITC Controller 3000 allow us to define proportionality setpoints with a precision of 0.001% in the irrigation water flow, each of which is personalised for the up to 6 mother solutions it is compatible with.
This precision combines with the precision provided by piston dosing pumps with micrometric and electronic regulation via a variable-frequency drive. The flow rates and volumes dosed are independent of the pressure, water speed, density and viscosity of the products dosed in agriculture, which can vary greatly.
It is also possible to manage dosing by conductivity, although this can’t be adjusted as quickly as proportionality. PI controls are usually used, which require a certain amount of time to reach the required value. This regulation works reasonably well with fertigation systems based on dosing pumps with variable-frequency drives that allow continuous flow injection, but it doesn’t work as well with fertigation systems based on intermittent injection, as it can affect their ability to reach the setpoint.
Managing by proportionality is recommended, as when dosing low concentrations of fertiliser, the lower end of the proportionality scale is much more extensive than it is with conductivity. Small differences in proportions don’t visibly affect the EC reading.
In order to achieve the optimal working pH, around 5.5, we need to use an accurate regulation system. In irrigation solutions, the main aspect that influences the acidity or pH of the water is the bicarbonate concentration. As pH is measured on a logarithmic scale, going down one point means having a H+ concentration that is ten times lower, meaning that in order to go down 0.1 points, we need 100 times less volume when we have a pH of close to 5.5 than when then pH is 7.5. On the other hand, the bicarbonate concentration and its buffering ability below pH 5.5 is so small that the in-line regulations must be performed very carefully if we don’t want it to decrease too much or become unstable.
It is important that we don’t overdo the acidity of the solution, as the solubilisation of aluminium can result in toxicity, which accentuates the need for accuracy in this control. The ITC Water Controller 3000 is capable of accurately controlling the in-line pH level, adapting it to changes in the network’s flow rate without moving from the setpoint, thanks to performing a PIQ adjustment of the pH, thus constantly monitoring the irrigation flow rate and anticipating the changes in the dose of acid.
Specific characteristics of blueberries nutrition
- High sensitivity to salinity, for which reason solid fertilisers should not be applied directly to the soil.
- Shallow root development with few root hairs. As they explore only a small part of the soil, this conditions the type of irrigation that we can use, which must be performed at a high frequency.
- They prefer acidic soil with lots of organic matter (OM).
- Their optimal pH is around 5.5.
- NH4+ demand in blueberries crops, which is possibly linked to their optimal pH level, a level which is well suited to keeping nitrogen in this form.
- A wide range of needs depending on the phenological condition of the crops, to which the proportion of the different nutrients must adapted.
- High concentrations of nitrogen must be avoided to prevent excessive vigour and increased sensitivity to pests, and it can also directly affect the quality of the fruit.
- Phosphorous is found in crops with poor root development, such as blueberries. Maintaining a low pH level and continuous dosing help minimise losses due to immobilisation.
- A good balance and minimum concentration of cations such as potassium, calcium and magnesium is needed.
- Too much potassium cracks the fruit and leads to deficiencies in magnesium and calcium, although a lack of it reduces the yield, as it limits the growth of the fruit. Calcium plays a vital role in determining the firmness of the fruit and how well it keeps post-harvest. This element is immobile in the plant, meaning that it must be supplied during each stage of the plant’s development, particularly in the days after the fruit begins to form. During the fruit growth stage, we must ensure sufficient levels of potassium, although not too much, as it is an antagonist of calcium.
What fertigation equipment is needed to grow blueberries?
The equipment installed must have the flexibility to allow us to change formulae (both the balance and concentration), allow a wide range of flow rates from one device, accurate pH adjustment and steady readings that are consistent with the setpoint, even when a very low pH is needed for fluctuating flow rates and, above all, as with any fertigation device, accurate dosing of low proportions of fertiliser that are not affected by a low pH.
