Deficit Irrigation Can Improve Fruit Quality for Hard Cider Producers

By Sarah Davis, Intern at Washington State University’s Tree Fruit Research and Extension Center and the Center for Sustaining Agriculture and Natural Resources

Apple trees with fruit on the branches, green foliage
Cider apples in mid August under RDI treatment. Photo: Sarah Davis.

Growing up, I remember my grandfather bringing my family fresh Honeycrisp apples from his orchard in the Chelan area, describing the qualities that made them special. As an orchardist, my grandfather always strived to have delicious, high-quality produce coming from his orchards. My grandfather is not alone in this quest; growers across the state are looking for ways to enhance the quality of their crops. As climate change progresses and temperatures rise, fruit quality could be affected: climate change has been linked to delayed fruit ripening, low fruit quality, low fruit yield, sunburn, and more.  Regulated deficit irrigation (RDI) is one possible way to combat some of these impacts. RDI is a practice that purposefully reduces water being applied to put mild stress on trees while not impacting the growth of the plant. RDI has been shown to increase sugar content, which is an essential aspect in cultivating high quality fruit. This summer during my research internship at WSU’s Tree Fruit Research and Extension Center in Wenatchee, I am looking at how regulated deficit irrigation in a commercial cider apple orchard affects plant stress  as well as fruit and cider quality. My internship ended before harvest took place, but here are some things that are already known about RDI and fruit quality and why it is an interesting practice to research.

Boxes of red apples
Box of Honeycrisp apples being sold at a supermarket. Photo: Christian M. M. Brady under CC BY-NC-ND 2.0.

Regulated deficit irrigation has been studied in both Honeycrisp apples and wine grapes. Honeycrisp apples have a tendency to become oversized, which increases the incidence of bitter pit and decreases their quality and taste. When RDI was applied in Honeycrisp in mid and late season, the size of the fruit was smaller than it was in normally irrigated trees. Markus Keller and colleagues observed a similar positive trend in wine grapes in southeastern Washington. After decreasing the water from 100% to 70% and 25%, they found that the 25% reduction put too much stress on the vines, affecting shoot growth, gas exchange, fruit development, and quality of fruit (Keller et al. 2016). However, there were no significant negative differences between the normally irrigated and 70% deficit irrigated crops with no inhibition of gas exchange, fruit growth, and fruit development. There was also evidence suggesting that the wine grapes in the deficit irrigation treatment presented with more fruit aromas, anthocyanin pigments, and potentially lower astringency, all of which are favorable for wine production.

With this in mind, it is possible to make connections between what is being seen in Honeycrisp and wine grapes to cider apples and cider production. The desired qualities in cider apples for cider production are a high sugar content to aid in fermentation, high acidity levels, polyphenols to enhance mouth feel, and firmness for pressing. In Braeburn cider apples, Miles and colleagues found that RDI decreased the size of cider apples which increased the firmness, soluble solids (proteins, fats, minerals, organic acids, carbohydrates, and minerals), as well as dry matter (Miles et al. 2020). The reduction of fruit size was beneficial for creating higher quality apples (and cider) because of the greater surface area to volume ratio which allowed for better pressing.

A branch of an apple tree loaded with apples
Cider apples in mid August under RDI treatment. Photo: Sarah Davis.

The project I was involved in is researching how RDI affects Golden Russet and Nehou varieties of cider apples. The purpose of the research is to see if water could be conserved by irrigating less while actually improving the quality of the cider apples. The experiment is taking place in a commercial orchard, and I discussed preliminary water conservation results in an earlier article.

While what we know about regulated deficit irrigation shows promise for producing higher quality fruit, wine, and cider, it is important to recognize that the research is still ongoing and implementing these practices could have unintended consequences. For example, since deficit irrigation is relatively new for cider apple cultivation and production, there is no guarantee that it is going to be profitable and sustainable in the long run. However, with these considerations in mind, it is plausible that purposeful deficit irrigation can be used to decrease fruit size. This would help with more efficient production of cider, higher sugar content, higher acidity, and higher polyphenol levels, all of which are essential for high-quality cider. Since climate change is shown to decrease sugar levels and development of fruit, RDI may be able to help maintain fruit quality as temperatures increase. Regulated deficit irrigation could be a potential tool for cider producers in Washington state to help increase the quality of their cider apples to create premium quality cider, while also conserving water.

References:

Keller, Markus, et al. “Deficit Irrigation Alters Grapevine Growth, Physiology, and Fruit Microclimate.” American Journal of Enology and Viticulture, vol. 67, no. 4, 2016, pp. 426–435., Online Access.

Miles, Carol A., et al. “Growing Apples for Hard Cider Production in the United States—Trends and Research Opportunities.” HortTechnology, vol. 30, no. 2, 2020, pp. 148–155., Online Access.