Characteristics analysis of marco-elements and mid-elements in Citrus leaves in Guangxi Province

【Objective】In recent years, citrus industry in Guangxi Province has developed rapidly be-cause of the continued high price of Shatangju and the introduction of high-sugar and low-acid of Orahvarieties, coupled with the spread of banana yellow leaf disease and the decline in sugarcane benefit. In2017, the planting area of citrus was 0.44 million hm2, and its output also reached 6.87 million tons, which accounted for 40% of the total annual fruit production in Guangxi Province. Abstract: The citrus growersin the province have overly relied on chemical fertilizers and used a large amount of N and P fertilizersfor pursuing higher-yield output, while ignoring the other elemental fertilizers, which caused the occur-rence of some problems such as the instability of citrus production, the deterioration of fruit quality andchlorosis symptom of deficiencies or toxicities, etc. In China, the research about balanced fertilizationin citrus guided by leaf nutrition diagnosis standard was still in its infancy. In order to explore the nutri-tional status of citrus trees in Guangxi Province, leaf macro-elements and mid-elements were systemati-cally studied, which provided a theoretical basis for balanced fertilization of citrus in this region.【Methods】In 2017, the collected leaf samples of citrus were from 207 orchards of 15 districts in Guangxi, Chi-na. 120 leaves were selected and collected in four directions from 30 trees per orchard. Then, macro-ele-ments and mid-elements of six-month-old spring flush leaves from nonfruiting twigs were analyzed.The results were divided into five categories: deficient range, low range, optimum range, high rangeand excess range, according to the guidelines for interpreting the standards of citrus tree leaf analysisfrom the integrate data in USA and China.【Results】The contents of nitrogen (N) , phosphorus (P) , po-tassium (K) , calcium (Ca) , magnesium (Mg) and sulfur (S) elements were (29.70±2.75) g · kg-1, (1.25±0.14) g · kg-1, (14.87±5.49) g · kg-1, (33.47±8.44) g · kg-1, (2.52±0.72) g · kg-1 and (3.03±0.62) g · kg-1, respec-tively. The lack of N and K contents coexisted with the excess. The orchards having leaf N and K con-tents with low range and below accounted for 13.53% and 30.43%, respectively, and those with highrange and above for 45.41% and 27.05%, respectively. The N content of 1/3 of citrus orchards inGuangxi Province remained high range and excess range, except for Long'an County, Mashan County, Quanzhou County and Laibin County. However, there was still insufficient of N content in some dis-tricts such as Debao County, Long'an County, Mashan County and Quanzhou County. It was worthmentioning that leaf N deficiency accounting for more than 50% orchards occurred in Debao County, Long'an County and Mashan County. Leaf K content in nearly 1/3 of citrus orchards was above opti-mum range. Among them, the orchards having leaf K content with high level and above accounted formore than half in Fuchuan County, Laibin City, Lingchuan County, Long'an County and ZhongshanCounty. In particular, over 80% of the orchards in Laibin City, Long'an County and Zhongshan Countywere above optimum range. Nevertheless, there were K insufficient problems in the leaves in nearly 1/3 of the orchards in Guangxi. Among them, the K content of more than 48% of the orchards in MashanCounty, Quanzhou County and Wuming County were at low range and deficient range. P, Ca and Mgcontents were mainly at optimum and low range, and the proportions at the optimum range were67.63%, 63.77% and 51.21%, respectively, while the proportions below the optimum range were32.37%, 35.75% and 48.79%. Except for Fuchuan County and Zhongshan County, the problem of P in-sufficiency existed in all the regions. Particularly, leaf P content in over half of orchards in Lipu County, Lingchuan County, Long'an County, Mashan County and Shanglin County had a low level. Leaf Ca in1/3 orchards was insufficient, and more than 50% of the orchards in Laibin City, Lingchuan County, Shanglin County, Xing'an County and Yangshuo County had a low Ca range. Leaf Mg content of near-ly 1/2 orchards were lack, and those being below optimum range accounted for more than half of the or-chards in Debao County, Laibin City, Zhangpu County, Lingchuan County, Long'an County, ShanglinCounty and Zhongshan County. In Lingchuan County, Long'an County, Shanglin County and Zhong-shan County, leaf Mg content in more than 50% of the orchards was at deficient level. 92.75% of the or-chards had a S content at optimum range.【Conclusion】Macro-elements and mid-elements of citrus or-chards in Guangxi Province showed obvious unbalanced nutrition. It is recommended that N and K fer-tilizers be added for the orchards with low contents, and controlled for those with high contents. More-over, a supplement of appropriate P fertilizer is needed. More importantly, Ca and Mg fertilizer are em-phatically complemented to ensure that the citrus trees grow up healthy with balanced nutrition.