Mineral Element Content of Orah Mandarin Grafted on Trifoliate Orange Rootstock in Nanning at Different Phenological Periods

Purpose This study aimed to clarify the annual mineral nutrient demand characteristics of Orah mandarin (Citrus reticulata×Citrus sinensis) grafted on trifoliate orange (Poncirus trifoliata) rootstock in Nanning, so as to provide a basis for scientific fertilization of Orah mandarin with this rootstock.

Methods Five-year-old Orah mandarin trees grafted on trifoliate orange were used as the test materials. Spring shoots and autumn shoots were sampled at 70 and 210 days after anthesis (DAA), and fruit samples were collected at 70, 150, 210, and 270 DAA, respectively. The mineral element contents of shoots and fruits at key growth stages were determined and analyzed.

Results The contents of N, S, Mn, B, and Al in autumn shoots were extremely significantly higher than those in spring shoots, the contents of Ca and Mg were significantly higher than those in spring shoots, while the Zn content was significantly lower than that in spring shoots, and no significant differences were observed in the contents of P, K, Fe, Cu, Mo, and Na between spring shoots and autumn shoots. Both N and S in the fruit maintained relatively high accumulation levels at 70-150 DAA and 150-210 DAA; the maximum accumulation of Ca, Mg, Mn, and Zn occurred at 70-150 DAA; P, K, B, Cu, and Mo exhibited high accumulation at 150-210 DAA; while the accumulation levels of Fe, Na, and Al peaked at 210-270 DAA. To produce 1 t of fresh Orah mandarin fruits, the fruit nutrient removal amounts were N 1.85 kg, P 0.18 kg, K 1.66 kg, Ca 0.57 kg, Mg 112.10 g, S 108.78 g, Fe 9.95 g, Mn 1.15 g, B 2.47 g, Cu 2.03 g, Zn 1.73 g, and Mo 0.05 g, with m_N∶m_P∶m_K of approximately 1.0∶0.1∶0.9. The period of 150-210 DAA was the peak stage of nutrient demand in the tree, during which fruit expansion and autumn shoot growth occurred simultaneously, imposing a dual nutrient consumption. Relatively high accumulation of Na and Al was detected in both shoots and fruits.

Conclusion Mineral nutrient accumulation of trifoliate-rootstock Orah mandarin shows obvious phenological periodicity, and autumn shoots possess a strong nutrient removal capacity. Theoretical calculation based on fruit nutrient removal indicates that the recommended fertilization rates of N, P, and K (measured by 667 m²) for high-yield orchards with a yield of 4 t per 667 m² are 37.04, 4.80, and 27.70 kg, respectively. It is necessary to control soil acidification in production to reduce the risk of aluminium toxicity.