Objectives Leaf microelement contents were analyzed to evaluate the microelement nutritional status of citrus trees in Guangxi Zhuang Autonomous Region, the biggest citrus production region in China, and to provide a theoretical basis for balance fertilization of citrus in this area.
Methods 207 representative citrus orchards in 15 main citrus production counties were selected for collecting leaf samples in 2017, and 5 essential microelements were quantitatively analyzed.
Results The ranges of the contents of Fe, Mn, Zn, Cu and B in citrus leaves were 37.9–278.5 mg/kg, 13.5–588.6 mg/kg, 5.4–68.2 mg/kg, 1.2–196.1 mg/kg and 32.9–281.1 mg/kg, respectively. The average contents of Fe, Mn, Zn, Cu and B elements were 99.6 mg/kg, 79.4 mg/kg, 20.1 mg/kg, 18.8 mg/kg and 111.3 mg/kg, respectively. The proportions of leaf Fe, Mn, Zn, Cu and B in the insufficient levels (deficient or low levels) accounted for 11.6%, 5.3%, 84.1%, 33.3% and 0.5%, respectively, and those in the optimum levels accounted for 67.6%, 72.5%, 15.9%, 34.8% and 41.5%, respectively, and those in the high or excess levels were 20.8%, 22.2%, 0.0%, 31.9%, and 58.0%, respectively. The leaf Fe contents were generally in the optimum level, except Quanzhou, Debao, Yangshuo and Xing'an County where the leaf Fe contents were relatively insufficient, and in Yongfu, Laibin, Long’an, Mashan County and Xixiangtang District where they exceeded the optimum levels. Insufficient leaf Mn contents were detected in orchards of Lipu, Lingchuan, Debao, Long’an and Mashan County. Except for Xing'an and Shanglin County, the orchards in the other 13 counties were excessive in leaf Mn contents, and in Yongfu, Yangshuo, Fuchuan, Zhongshan, Lingchuan, Laibin, Long'an and Mashan County, more than 25% of orchards were exceeding in leaf Mn contents. The percentage of orchards with insufficient leaf Zn contents were the highest among the five micronutrients. The Zn contents in leaf samples of Quanzhou, Fuchuan, Xing’an, Lingchuan, Debao, Long’an, Mashan and Shanglin County were 100% insufficient. The leaf Cu contents fluctuated greatly in different orchards, and the percentages of leaf samples with insufficient, appropriate, and excessive levels, each represented around one third. The Cu contents of leaf samples of Quanzhou, Lipu, Lingchuan and Debao County were mainly in the insufficient level, and the contents in Yongfu, Yangshuo, Xing’an, Zhongshan and Mashan County were mainly in the optimum level. However, the Cu contents of leaf samples of Fuchuan, Wuming, Laibin, Xixiangtang, Long’an and Shanglin County were mainly in the excess level. Orchards with excess leaf Cu contents were mainly planted with varieties susceptible to canker disease, which was related to the frequent application of copper containing bactericide. The proportion of leaf B contents exceeding the optimum level was the largest, reaching 58.0%. The leaf B contents in Quanzhou, Yangshuo, Zhongshan, Debao and Shanglin County were mainly in the optimum level, while the leaf B contents in Yongfu, Lipu, Xing’an, Wuming, Laibin, Xixiangtang, Long’an and Mashan County were mainly in the excess level.
Conclusions Most of the analyzed citrus orchards have one or several micronutrients in insufficient or excessive status. In general, Fe, Mn and Cu nutrition in most citrus orchards is in optimum level, and insufficient and excessive contents are also detected. Zn deficiency is widely happened while B contents often exceed optimum level. In production practice, special attention should be paid to supply Zn fertilizer and reduce the application of B fertilizer.
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