Preharvest calcium sprays and fruit calcium absorption in Golden "apples"

TL;DR: In this article, a study was carried out in the Experimental Station of Lleida, with five year-old ‘Golden Smoothee’ apple trees on M9 Pajam 2® rootstock.

Abstract: Calcium (Ca) is one of the most important elements in apple fruit quality. The difficulty in supplying enough Ca to the fruit is a key point to ensure an adequate content of this element at harvest and after cold storage. The study was carried out in the Experimental Station of Lleida, with five year-old ‘Golden Smoothee’ apple trees on M9 Pajam 2® rootstock. The assay was divided in two parts. The first experiment consisted of the evaluation of fruit Ca absorption. One group of trees were sprayed with 0.15% calcium solution every two weeks during the season, the other group remained untreated. Results demonstrated that fruit Ca absorption rate in ‘Golden’ apples was more intensive during the first half of the fruit growing season than in the second half, decreasing dramatically until harvest. Even though Ca sprays were applied during the entire season, the amount of fruit Ca influx during the first period was similar in treated and untreated fruits. However, during the second period, treated fruits accumulated more Ca and final Ca contents were higher. In the other experiment, 10 or 6 Ca sprays were applied every two weeks period, starting 10 days after full bloom and at June 1st, respectively. Sprayed fruits had greater Ca content, better quality and cold storage aptitude, and fewer fruit disorders. Although other fruit nutrient contents were not altered by Ca sprays, Ca-related nutrient ratios like N/Ca and (K+Mg)/Ca gave more balanced values. Both application strategies, exhibited similar results and 10 treatments did not improve Ca content in the fruits compared with 6. The same treatments were also applied in commercial orchards and similar values were obtained. In conclusion, there was no apparent response to spraying with Ca during the first growing period, while Ca is mainly provided by root absorption. However, in the second part of the season, when fruit Ca absorption is limited, foliar applications were more effective and fruit Ca accumulation increased.