Soil pH plays a key role in blueberry production because it determines the form and availability of nutrients that will be absorbed by the plant for fruit development. Poor management can lead to nutritional deficiencies, loss of fruit quality, and even deterioration of the crop.
In this context, understanding what pH is, how it works, and what the optimal ranges are is essential to avoid mistakes and maximize the productive potential of the crop.
What is pH and why is it so important in blueberries?
pH, or potential of hydrogen, measures the concentration of hydrogen ions (H⁺) in a solution. This parameter directly affects nutrient availability, as it determines the chemical form in which nutrients occur and whether they can be absorbed by plant roots.
In blueberries, this aspect is particularly important, as they are an acid-loving species adapted to grow under acidic conditions, although with clear limits regarding their optimal development range.
According to Sebastián Ochoa, director of Consultora Agrícola y Comercial Santa María (CASM Blueberries): “Blueberries are an acid‑loving plant capable of tolerating low and very acidic pH levels, unlike many other species. However, tolerating acidic pH does not mean the ideal pH should be extremely low. When pH decreases excessively, several nutrients become less available, which ultimately affects fruit quality.”
According to the international advisor, the optimal pH range for blueberry cultivation is between 5.5 and 6.0, the interval where the highest availability of essential nutrients for the plant is achieved.
The impact of pH is not limited to a single nutrient; rather, it regulates the availability of both macro- and micronutrients in an integrated way. Fernando Villagrán, international advisor in blueberry production at CASM Blueberries, explained: “pH regulates the availability—or lack of availability—of macro- and micronutrients. When working with high pH, micronutrient deficiencies occur; and when pH is too low, deficiencies of both macro- and micronutrients may appear.”
High pH, bicarbonates and chlorosis: a critical problem
One of the main problems associated with pH levels above 6.0 is the presence of bicarbonates in the soil solution. Blueberries are a calcifuge species, meaning they do not tolerate alkaline soils or the presence of bicarbonate or calcium carbonate.
Ochoa explained that when pH exceeds 6.0, bicarbonates begin to appear in the soil solution, which directly interferes with iron metabolism. “The plant may absorb iron, but it is unable to metabolize it. As a result, chlorophyll levels begin to decline, the leaves turn yellow, the photosynthetic rate decreases, and in extreme cases the plant may eventually die,” he stated.
“For this reason, maintaining pH between 5.5 and 6.0 not only helps neutralize bicarbonates—since they do not disappear—but also ensures a high availability of nutrients for the crop,” the specialist emphasized.
In this regard, Villagrán noted: “At pH levels below 5, iron is present in the ferrous form, that is, in a form that is poorly absorbed by the roots. At such pH levels, magnesium increases considerably, which interferes with iron absorption. The highest availability of this element is achieved at a pH of 6.”
Use of acids: types, advantages and precautions
To neutralize the bicarbonates present in irrigation water, different types of acids are used. Among the most common are:
- Nitric acid (HNO3)
- Sulfuric acid (H2SO4)
- Sulfurous acid (H2SO3)
- Phosphoric acid(H3PO4)
However, each of these acids has particular characteristics and acidifying properties that must be carefully considered.
In the case of phosphoric acid, for example, excessive application may cause problems, Ochoa warned. “A high phosphorus supply can lead to the formation of insoluble salts, such as calcium, iron, or zinc phosphates, leaving these elements unavailable to the plant.”
According to Ochoa, sulfuric acid is the most recommended option, as it does not interfere with crop nutrition. Nitric acid, on the other hand, provides nitrogen, so its use must be considered within the nutritional plan. Sulfurous acid, produced from the combustion of sulfur, is a weaker acid, which allows for more controlled dosing.
Common mistakes in pH management
When discussing pH management, one of the most common mistakes among growers is excessive dosing, based on the belief that, because blueberries are an acid-loving species, they must grow in extremely acidic soils.
“The pH is lowered too much, which affects nutrient availability and directly impacts fruit quality,” Ochoa noted.
Other common mistakes, the international advisor explained, include the excessive use of phosphoric acid, incorrect acid dosing, or working with pH levels between 6.0 and 6.5, where bicarbonates are still present and can affect the plant.
“Blueberries absorb nutrients in two ways: a passive mechanism, through the flow of water and dissolved nutrients, and an active one, in which the root releases protons to facilitate ion exchange and the uptake of cations. This process causes natural acidification of the rhizosphere, especially in substrate-based systems. In these cases, it is common for the pH measured in the drainage to be much lower than the pH of the solution applied through drip irrigation,” he explained.
In this case, the mistake lies in trying to correct that low pH by increasing the pH of the nutrient solution. “By doing so, bicarbonates are ultimately supplied to the plant, which leads to chlorosis and nutritional problems.”
Villagrán reinforced the idea that pH should be managed in balance, within a range between 5.5 and 6.0. “In the fertigation solution, we must consider that blueberries have their own mechanisms to acidify the rhizosphere and absorb nutrients.”
Best practices for proper pH management
To avoid mistakes and ensure efficient nutrition, specialists agree on a series of key recommendations:
- Use reliable water analyses, conducted at least once a month.
- Monitor bicarbonate concentrations, as they may vary depending on the water source.
- Use automatic injection systems that adjust the acid dose in response to changes in pH.
- Periodically measure the pH in the drip system to verify that the applied value is maintained in the orchard.
- Conduct soil or substrate analyses, and in substrate-based systems, perform drainage analyses to evaluate the actual behavior of pH.
“Precise pH management not only prevents nutritional problems but also becomes a strategic tool to improve fruit quality, production efficiency, and the sustainability of blueberry cultivation in Peru,” the experts conclude.
