Effects of soluble potassium silicate soil drenching on sweet cherry fruit quality

Fruit firmness (g mm-1) and stem-pull force (g) (retention force between the pedicel and the fruit) are important factors affecting marketability of fresh sweet cherry fruit; USA export minima are >700 g mm-1 and >250 g, respectively. Up to 3 soil applications of soluble 1% potassium silicate (28% Si) applied to the drip area, every 3 weeks from flowering, had an effect on both parameters. In 2007, at harvest, treated ‘Bing’ fruit were firmer (P<0.001) than untreated control fruit (409 v. 386 g mm-1). In 2008, treatments had no effect on ‘Bing’ fruit firmness at harvest; however, after 2 weeks of regular atmosphere storage at 2°C, treated fruit were firmer (329 g mm-1) than untreated control fruit (320 g mm-1) (P<0.001). Treated ‘Royal Rainier’ fruit were firmer at harvest (291 g mm-1) than untreated control fruit (274 g mm-1) as well as after 2 weeks cold storage (289 v. 269 g mm-1). Treated ‘Sandra Rose’ fruit also were firmer at harvest (289 g mm-1) than untreated control fruit (282 g mm-1) (P<0.001). In 2008, stem pull force of all untreated fruit decreased between the day of harvest and 2 weeks of cold storage (‘Bing’ = 1008 g to 816 g; ‘Royal Rainier’ = 1213 g to 1097 g; and ‘Sandra Rose’ = 992 g to 815 g, respectively) (P<0.001). In contrast, stem pull force of all treated fruit decreased less after two weeks cold storage (‘Bing’ = 1,026 g to 890 g; ‘Royal Rainier’ = 1,165 g to 1,159 g; and ‘Sandra Rose’ = 1,052 g to 1,002 g) (P<0.001). Our preliminary findings suggest that regular soil-drenching of cherry trees with soluble potassium silicate during the growing season has the potential to increase cherry fruit firmness and stem pull force without affecting fruit size or sweetness negatively.