关键词: 三峡重庆库区, 塔罗科血橙, 施氮水平, 氮肥减量, 养分, 果实产量与品质

Abstract:

【Objective】 This study investigated effects of different nitrogen application levels on nutrient uptake, fruit yield and quality, soil physical and chemical properties of late ripening citrus Tarocco blood orange in typical citrus orchards to provide a theoretical basis for the high-quality and high-yield of late-maturing citrus in the Three Gorges area of Chongqing city. 【Method】 Six different nitrogen treatments (N0 (0), N1 (1 kg/plant), N2 (1.5 kg/plant), N3 (2 kg/plant), N4 (2.5 kg/plant) and N5 (3 kg/plant)) were performed to study its effects on nutrient absorption of branches and leaves and fruit, fruit quality and yield and soil physicochemical properties using 7-year-old Tarocco blood orange grafted on Poncirus trifoliata (L.). 【Result】 Results showed that the increased nitrogen levels except N2 group significantly increased the dry matter amount of leaves and branches in different periods of blood orange with higher level in spring shoots than autumn shoots as well as higher level in leaves than branches. The nutrient absorption of nitrogen, phosphorus and potassium in spring shoots was the lowest under N0 treatment, and the absorption of nitrogen in leaves was significantly increased by the added nitrogen fertilizer with a peak level under N2 treatment while the absorption of phosphorus and potassium with a peak level under N3 treatment. Nitrogen application significantly increased the amount of nitrogen uptake of leaves and branches of autumn shoots with a maximum level under N5 treatment. High nitrogen treatments (N3-N5) significantly increased the amounts of phosphorus and potassium uptake of leaves and branches. Nitrogen first increased then decreased the nitrogen and potassium content of fruit with the maximum level under N2 treatment. The content of nitrogen and potassium in pulp was much higher than that of peel, while the phosphorus content was opposite. The maximum nutrient removal amount of nitrogen, phosphorus and potassium was found under N2 treatment with a significant increase, and the amount of nutrient removal was potassium>nitrogen>phosphorus. The pH value and content of organic matter of soil decreased significantly by adding nitrogen fertilizer while the content of available nitrogen and phosphorus of soil increased significantly with the maximum available potassium content under N3 treatment. Nitrogen increased the leaching of nitrate nitrogen in soil within 0-20 cm with the highest level under N2 treatment. Ammonium nitrogen was positively correlated with the nitrogen application rate. There was no significant difference among the content of nitrate nitrogen and ammonium nitrogen under all treatments within 20-40 cm soil layer. The content of nitrate nitrogen in 40-60 cm soil layer increased significantly under high nitrogen treatments, while the ammonium nitrogen content did not change. Nitrogen application first enhanced the thickness of pericarp, the longitudinal diameter, transverse diameter, average weight and yield, and then decreased with the highest level of the longitudinal and transverse diameter under N3 treatment and the highest weight and yield under N2 treatment. Nitrogen application first increased then decreased the total soluble solid (TSS) content without significant difference. Nitrogen input increased titratable acid (TA) content and but decreased TSS/TA ratio. N2 group had the highest vitamin C and anthocyanin content. Fruit coloration was relatively good between N2 and N3 treatments. Correlation analysis showed that the nitrogen content in leaves was positively corrected with the TA content of fruit and the thickness of pericarp, and negatively correlated with the ratio of TSS/TA, and the content of available N in soil was positively correlated with TA content and pericarp thickness, which was significantly negatively correlated with TSS/TA ratio of fruit.【Conclusion】Considering and analyzing, in the citrus orchard of the Three Gorges area of Chongqing, the recommended pure nitrogen application rate was ranged from 0.63 to 0.86 kg/plant which can guarantee a high level of yield and fruit quality, and is beneficial to the nutrient absorption and utilization of blood orange tree, while the risk of orchards’ soil environmental pollution was relatively low.

Key words: Three Gorges area of Chongqing city, Tarocco blood orange, nitrogen application level, nitrogen reduction, nutrition, fruit yield and quality