Fertigation of blueberries is one of the techniques that requires greater precision due to the demands of this crop.
This is due to the combination of high nutritional requirements with low tolerance to salinity and low volume explored by its roots, which require continuous dosing to meet the required fertilizer units without saturating the soil with salts.
How should blueberry fertigation be done?
The fertilization of the blueberry requires a distribution of the fertilizers in the maximum time: the greater the volume of irrigation water containing the nutrients, the less salinity will be induced. It is therefore necessary to take advantage of every irrigation opportunity to fertilize and to minimize the supply of water without fertilizer.
In those cases where, due to the initial water characteristics or the soil analysis, it is necessary to wash out the salt and guarantee a drainage fraction, it is possible to establish a pre-irrigation without fertilization.
Once the fertigation strategy has been decided, application control is key to ensure that the intended formula is faithfully transferred to the irrigation solution.
聽Specific Nutritional Properties of Blueberries
The cultivation of blueberries has specific needs due to its nutrition.
The following are the characteristics that must be taken into account:
- High sensitivity to salinity. It is not advisable to use solid fertilizers for blueberries applied to the soil.
- Shallow root development with few root hairs. Conditions the type of irrigation, which should be high frequency.
- Prefer acid soils with high OM (organic matter)
- Optimum pH around 5.5
- Appetite for NH4+ in blueberry cultivation, possibly associated with the optimum pH of cultivation that favors the maintenance of nitrogen in this form.
- Requirements vary according to the phenological stage of the blueberry, and the different nutrient ratios should be adjusted accordingly.
- High concentrations of N should be avoided to prevent problems of excess vigor and greater sensitivity to pests, as well as directly affecting fruit quality
- P favors crops with poor root development such as blueberries. Low pH setting and continuous dosing helps to minimize immobilization losses
- Balance and minimum concentration of cations such as K, Ca, Mg is necessary
- Excess K causes fruit cracking and induces Mg and Ca deficiencies, but its deficiency reduces yield by limiting fruit growth
- Ca plays a crucial role in fruit firmness and post-harvest preservation. This element is immobile in the plant, so it cannot be deficient throughout fruit development, especially in the first days after fruit set.
Aspects to consider in blueberry fertigation
It should be noted that dosing by time through precise flow rate dosing systems forces the calculation of volume, translated into programming time, for each sector.
In this system, batches of water with and without fertilizer are produced in the same irrigation operation, increasing the salinity of the nutrient containing batch and making it less accessible to the crop. This disadvantage can be solved by dosing proportional to the instantaneous flow rate and by controlling the electrical conductivity (EC).
In fact, dosing proportional to the instantaneous flow rate, measured by a high frequency flowmeter, guarantees the exact concentration of each nutrient in a very precise way.
Blueberry fertigation equipment
The equipment installed for berry fertigation must ensure flexibility in changing formulations (both in balances and concentrations), allowing a wide range of flow rates from the same equipment, precise pH adjustment to obtain stable readings, and high accuracy in dosing low fertilizer proportions that are not altered by low pH setting.
Equipment such as ITC’s Controller 3000 allows the definition of dosing instructions with an accuracy of 0.001% of the irrigation flow rate, independently for each of up to 6 different stock solutions.
This precision is combined with that offered by plunger dispensers with micrometric and electronic regulation by means of a frequency converter.
The flow rates and dosed volumes are completely independent of the pressure, water velocity, density and viscosity of the products dosed in agriculture and can be adjusted over a very wide range.
It is also possible to control dosing by conductivity, although the response is not as fast as in the case of proportionality. Normally, PI type controllers are used, which take some time to reach the required value.
Proportionality control is recommended because when low fertilizer concentrations need to be dosed, proportionality has a much wider range than conductivity. Small differences in proportionality will not significantly change the EC reading.
Optimum pH in blueberry crops
The optimum working pH is around 5.5 and requires a precise control system.
In irrigation solutions, the main factor influencing the acidity or pH of the water is the concentration of bicarbonates. Since pH is a logarithmic scale, this means that to decrease one point, the concentration of H+ must be ten times lower, so to decrease 0.1 points, we need 100 times less volume when we are close to pH 5.5 than when we are at pH 7.5.
On the other hand, the concentration of bicarbonate present and the buffering capacity are so small below 5.5 that on-line adjustments must be made very carefully if we do not want to go too low or enter into instability.
If acidification is exceeded, the solubilization of aluminum can cause toxicity, further emphasizing the need for precision in this control.
The Water Controller 3000 allows precise on-line pH control by adapting to changes in the network flow rate without moving from the set point, thanks to the PIQ type pH adjustment that constantly monitors the irrigation flow rate and anticipates changes in acid dosage.
