Field experiments of nitrate treatment on ‘Fuji’ trees
For field experiment, 2-year-old ‘Fuji’ trees were selected as experimental material. ‘Fuji’ trees were planted at National Engineering Research Center for Apple of Shandong Agricultural University. Line spacing × plant spacing is ~ 2 meters × 0.7 meters. Each line contains 11 trees. Since April 2018, the trees were treated with 10, 30, 60 or 120g KNO3 fertilizer per plant, respectively, with KCl was added to maintain the same K+ concentration. KNO3 fertilizer was applied to the left side of the tree, near the root. The treatment was performed once a month until June. KNO3 fertilizer was purchased from Shandong Agricultural University Fertilizer Technology Co., Ltd. (Tai’ an, China).