Effects of different potassium fertilizers on production, quality and storability of Fuji apple

【Objectives】 Generally, apple trees need a large amount of potassium (K) nutrient, while in Shaanxi province, apple growers normally apply less amount of K fertilizer, and moreover, high population density per unit area is adopted in recent years. Apple orchards in Shaanxi are in K deficiency. It is very important to be considered to reach adequate K fertilization for apple. Therefore, two kinds of K fertilizers were used in this experiment to study their effect on tree growth, nutrient absorption, apple quality and yield and postharvest storage quality. The aim was to achieve scientific recommended use of K fertilizer on apple production.【Methods】 A two-year field experiment was conducted in Fengxiang, Shaanxi from 2011 to 2013 on 8-year Fuji apple trees to investigate the effect of different potassium (K) fertilizers on nutrient uptake and new shoot growth of apple trees, the fruit quality and yield and postharvest storage quality (firmness, soluble solids, titratable acidity and rotten ratio). There were three treatments without K (CK), KCl and K2SO4 with 3 replications according to the complete randomized block design. The same amount of K2O was utilized for different K fertilizers and other fertilizers (N and P) were applied in the same rate in each treatment.【Results】 1)The mean shoot lengths of the CK, KCl and K2SO4 treatments are 18.25 cm, 17.83 cm and 19.39 cm respectively, and they are not significantly different. Compared to CK, the KCl and K2SO4 treatments increase the N and P contents in leaves, and meanwhile decrease the Ca and Mg contents in leaves. The leaf N and P contents of the K2SO4 treatment is significantly higher than those of CK. 2)The average yields in the two years are significantly different among the treatments as KCl K2SO4CK. 3)Average fruit weight of KCl treatment is significantly higher than others, and the weights are 267.42 g, 304.72 g and 287.73 g per fruit in CK, KCl and K2SO4 treatments respectively. In addition, the fruit ratios with above 80 mm diameter in the KCl and K2SO4 treatments are 14.9% and 11.5%, higher than that in the CK treatment. 4)Compared to CK, the KCl and K2SO4 treatments increase the N and P contents and accumulation in fruits but reduce the Ca and Mg contents and accumulation. In addition, the N and P contents and accumulation in fruits in the KCl treatment are higher than those in the K2SO4 treatment. Nevertheless, the K contents in fruits are similar among the 3 treatments. 5)Both the KCl and K2SO4 treatments lead to a lower fruit fresh firmness (but not significant) in 10 days after commercial harvest compared with the control treatment, however, the titratable acidity, soluble sugar and vitamin C contents are increased under the KCl and K2SO4 treatments. During storage period under room temperature, the titratable acidity contents of all treatments are declined gradually, and the soluble solid contents in the KCl and K2SO4 treatments are increased, while it declined constantly in the control treatment. At 90 days after the harvest, the fruit firmness rates are decreased by 19.23%, 6.96% and 22.19% in the CK, KCl and K2SO4 treatments respectively, meanwhile the ratios of rotten apples are 11.11% in CK, 9.25% in KCl and 5.55% in K2SO4 treatment.【Conclusions】 In this short term experiment, KCl fertilizer is better than K2SO4 in yield, fruit size, fruit quality at commercial harvest, whereas K2SO4 fertilizer enhances the plant growth, increases the nutrient uptake in leaves and prolong the storage life.