Comparison of mineral elements between fruit and vegetative branch leaves of the Chinese winter jujube during the fruit development stage

To provide a theoretical rational fertilization basis for improving the quality of Chinese winter jujube, we studied the contents of N, P, K, Ca, Mg, and Na in its fruit and vegetative branch leaves at different fruit development stages (initial-bloom, full-bloom, after-flowering, hardcore, and mature stages) and analyzed N/P, K/Na, Ca/Na, and Mg/Na ratios. The results indicated that from the initial-bloom to mature stage, the N and P contents showed a downward trend, and K content increased gradually during the fruit development stage of Chinese winter jujube; however, the Ca and Mg contents in leaves increased initially and then decreased. The Na content in leaves showed a slight change, but increased suddenly in the mature stage. In the above stages of fruit development, the K content in fruit branch leaves was higher than that in vegetative branch leaves, whereas the N, P, Ca, Mg, and Na contents in fruit branch leaves showed the opposite trend. Variance analysis showed that there was a significant difference (P < 0.05) in Ca and Mg contents between the fruit and vegetative branch leaves during full-bloom and after-flowering stages. The N content was significantly different only during the full-bloom stage. There was no significant difference in K and Na contents between the two types of leaves during the fruit development stage. The analysis of element content ratio in the leaves showed that N/P increased gradually from the full-bloom to mature stage, with values > 16, indicating that the growth of Chinese winter jujube leaves was mainly restricted by P content during these stages. The analysis also showed that K/Na, Ca/Na, and Mg/Na in fruit development stages changed similarly with the K, Ca, and Mg contents, respectively. The correlation analysis showed that N/P was mainly determined by the P content, Ca/Na was determined by Ca and Na contents, and Mg/Na was determined by Mg and Na contents, whereas K/Na in vegetative branch leaves was mainly determined by Na content. In summary, the full-bloom to after-flowering stage (June-July) was a relatively stable period of mineral elements in Chinese winter jujube, which could be used as a suitable period for the nutritional diagnosis of this species. Simultaneously, Ca and Mg fertilizers should be appropriately applied to the fruit branch leaves during this period to ensure the fruit quality and yield of Chinese winter jujube.