Influence of various phosphorus and potassium rates on juice vitamin C, P-carotene, and lycopene concentrations of Flame grape fruit

摘要

Flame grapefruit trees on Swingle citrumelo rootstock were planted in 1998. Phosphorus fertilizer was applied at 0, 48 (optimal), and 96 (high) kg P/ha in 1999-2000 to establish a range of soil-test P, and none was applied since Spring 2000. Potassiumfertilizer was applied every year since planting at 0, 186 (optimal), and 372 (high) kg K/ha. The P and K treatments were applied in all factorial combinations. Nitrogen and other cultural practices followed the recommendations (www.CREC.IFAS.UFL.EDU) for citrus production. Fruit were harvested in January 2003 and 2004, respectively, equally from all sides of the tree from 5 blocks totaling 25 trees. Harvested fruit were hand-juiced and prepared for vitamin C, and pigments analysis by an HPLC system coupled with analysis-specific columns. The results indicated that vitamin C was higher in year 2004 than 2003 fruits. The highest vitamin C was in the treatment block without P and optimal K (0 x 186) while the lowest was found in the optimal P and non-K(48 x 0) block among the five treatments. In turn, P-carotene and lycopene were the highest in the optimal P and non-K (48 x 0) treatment during year 2003 and 2004, respectively. No significant difference was found among the rest of treatments. The studydemonstrated that high level of P or K does not increase the fruit vitamin C, and pigments concentrations. Increasing P and K fertilization rates does not increase the fruit internal nutritional value of the desired and healthful compounds found in Flame grapefruit.