To face the long drought suffered by Chile and the increase in international competitiveness in the blueberry market, Arthur Calderon presented the results of his research in the talk entitled "How to determine the frequency of irrigation in blueberries?" during the Technical Workshop "Varietal exchange and optimization of the agronomic management of blueberries to improve yields and fruit quality in the southern zone of Chile" organized by the Chilean Blueberry Committee (ASOEX).

“Better measurements are better decisions”

The wedge of the title was affirmed by Calderón while showing through photos the construction of a test pit, a necessary intervention for an economic and affordable form of measurement for small and medium producers: humidity sensors. In the test pit, a grid is established where the different soil moisture measurements are assigned by area. In this way, it is possible to understand how irrigation water is distributed and the needs of the plant's root system.

“This modernization also requires knowing your soil. Using the sensor requires knowledge of soil physics and the moisture retention curve. It is not enough to just look at the graphs, since, for example, at the same humidity measurement, a clay soil can be further from its field capacity than a sandy one”, he stressed.

In addition, the doctor of horticulture and agronomy from the University of California Davis explained that the system explained above is not exact. “Soil moisture is not linearly related to the water status of the plant”, establishes the researcher based on his studies. 

Regarding other measurement methods, Calderón stated that “generally, the most expensive are those stations that have telemetry. They are stations that have the capacity to measure at different depths, and that are associated with management software where you can see on your phone or computer, the drying of the soil at different depths. Its cost can greatly exceed 3 million pesos”, indicating its negative effect on the profitability of medium and small agriculture. 

Water stress in protected agriculture

Water potential quantifies the tendency of water to flow from one area to another by osmosis, gravity, mechanical pressure, or metric effects. This flow is lower the more severe the water stress, becoming an indicator of the latter phenomenon.  

Calderón decided to investigate the effect of water potential on the stomatal behavior of leaves, in scenarios of moderate-severe, mild-moderate water stress, and without water stress, using blueberry crops protected by rufia, mesh, plastic or without protection (at fresh air).

The closure of the stomata of the leaves is one of the first responses of the plant to water stress, limiting the photosynthesis process and the entry of carbon dioxide into the plant, which ends up reducing the quality and quantity of the fruits.

The results of the study showed that the crops covered with mesh have the worst stomatal conductance of the leaves when there is moderate-severe water stress, the worst of the three indicators. However, the relationship between stomatal behavior and water potential is not linear for blueberries outdoors and covered with netting.

Thus, when water stress is mild-moderate, the mesh cover has better water potential than the other crops studied (raffia, plastic or open air). 

On the contrary, when the water stress of the plant is moderate-severe, the type of crop with the best result is the one covered with raffia, slightly surpassing the crop covered with plastic.

After his presentation, the expert was asked about the most "sensitive" moments for irrigation during blueberry cultivation, a term he mentioned during his talk. In this regard, he pointed out that although to obtain good quality, all production can be sensitive to water stress, he highlights "stage 1" (initial) of the berry crop as key.

“It is when cell division occurs, all the cells that are going to be in that blueberry fruit at the end of the season, are produced during the first 30 days, and cell elongation also occurs, which is what is going to give us about 60-70% of final size. So this time, from a caliber point of view, is the most relevant.”

Finally, the expert closes by calling for research on the relationship between irrigation and the different varieties of blueberries. “When one does a survey on the importance of irrigation for production, more than 80% say that it is extremely important. And when you ask how much time you spend running an irrigation schedule, it's less than 10% of the time worked. So it is extremely important that specific studies are carried out that allow us to understand this relationship.”