A summary of a presentation by Dr. Yan Wang, Assistant Professor, Postharvest Physiology, Oregon State University at the Washington Tree Fruit Research Review 2016. Summarized by Tianna DuPont, WSU Tree Fruit Extension. Reviewed by Dr. Yang Wang. February 5, 2017.
Calcium is critical for strong cell walls and good postharvest quality of fruit. Cherry fruit needs 600-800 ppm of calcium in order to have good storage quality. When calcium concentrations are lower pitting is more likely and fruit flavor may not be as good after shipping. However, often fruit is calcium deficient. From 2013 to 2015 Yan sampled five to ten orchards per cultivar and found variable calcium levels in fruit.
How Do We Increase Calcium Content in Fruit?
Calcium management should be part of an integrated program.
- In order for trees to take up calcium they need to have healthy root systems. If you have a calcium related issue check for root disease and consider soil tilth and watering schedules to make sure your tree roots are not impacted by saturated or compacted soils.
- Monitor calcium availability in soil. Calcium sprays are designed to supplement not replace calcium uptake from soil. Target a soil calcium range of 600 to 4,000 ppm. Monitor pH which will effect nutrient availability. Consider the ratio of calcium to cations such as potassium.
- Irrigation. Sufficient irrigation is critical for calcium uptake in the plant. Calcium deficiency is often related to insufficient irrigation. In the middle of a hot summer your trees may be using three acre inches of irrigation per week! Monitor evapotranspiration and soil moisture to ensure sufficient but not excess irrigation.
- Balance fruit and vegetation. Leaves have more surface area and so they are transpiring more than fruit. This means that as calcium in soil water is pulled through the plant’s water moving tubes (xylem) more of it is deposited in leaves than fruit. Good crop load management helps ensure that sufficient calcium is deposited in fruit which are at a natural disadvantage because they transpire less.
- Supplementary calcium sprays. Six weekly sprays of Ca(NO3)2 or chelated Ca sources (Ca2+ at 0.1-0.15%) between pit hardening and harvest has been shown to increase calcium quantity in fruit and postharvest quality. Greater than 0.2% Ca2+ increases risk of leaf burning and reducing fruit size.
For example, using a calcium nitrate product with 11% calcium 1 gal per 100 gallons would give growers 0.11% calcium within the 0.1 to 0.15% range. 2 gallons per 100 gallons of a calcium nitrate product with 7% calcium would give 0.14% also within the 0.1 to 0.15% range.
In Dr Wang’s recent study he found that the previous recommendation of three calcium applications did not increase concentrations of calcium in the fruit. Six applications between pit hardening and harvest was able to increase calcium levels from 450 to 650 ppm. Nine applications did not do a better job than six. Early applications before pit hardening were also not effective. The concentration of Ca2+ was also important. Ca2+ between 0.1 and 0.15% performed the best. Ca2+ of greater than 0.2% increased the potential for leaf burning and reductions in fruit size. Ca(NO3)2 or chelated Ca is recommended. Calcium chloride is not recommended on cherries.
Assistant Professor, Postharvest Physiology
Oregon State University