Effect of Foliar Spraying of KH2PO4 on Mineral Nutrients and Sugar-Acid Profile in Pineapple Fruits

【Objective】This study aimed to investigate the effects of foliar application of potassium (K) fertilizer at different concentrations on mineral element absorption and sugar-acid metabolism in 'Golden Pineapple (MD-2)' during fruit development, providing theoretical support for high-quality pineapple cultivation.【Method】Using 'MD-2' as the test material, three KH2PO4 concentrations treatments were applied: 0.3% (K0.3), 0.6% (K0.6), and 0.9% (K0.9), with water as the control (K0, CK). The fresh mass, dry mass, moisture content, mineral element content and sugar-acid component differences of fruits at the harvest period were determined by methods such as Kjeldahl nitrogen determination, spectrophotometer, flame method and HPLC.【Result】Foliar spraying of different concentrations of KH2PO4 significantly increased the fresh and dry weight of pineapple fruits and promoted the effective accumulation of biomass. Compared with K0 (CK), the increases in fresh and dry fruit quality after potassium fertilizer application were 4.0%-36.4% and 29.3%-52.5% respectively, with K0.9 and K0.6 performing better. The increase in the concentration of potassium sprayed reduced the water content of pineapple fruits, from 82.3% to 79.2%. The appropriate potassium concentration for spraying can significantly increase the contents of K, N and P in pineapple fruits by 5.3%-19.4%, 3.3%-12.9% and 17.0%-40% respectively, and the highest was achieved with K0.6 treatment, which were 14.58 g/kg, 3.47 g/kg and 0.66 g/kg respectively. Meanwhile, compared with K0 (CK), moderate application of potassium fertilizer helps to balance the nutrients of pineapple fruits and improve their nutritional quality. Spraying potassium fertilizer has a relatively small effect on the titratable acid content of fruits, but has a significant effect on Vc, total soluble sugar content and sugar-acid ratio. Among them, the Vc content of fruits decreased significantly with the increase of the concentration of sprayed potassium fertilizer. Compared with K0 (CK), the Vc content of fruits treated with K0.9 decreased by 21.18%. The total soluble sugar content of the fruit increased by 1.94%, and the sugar-acid ratio increased by 11.1% to 13.4%. Moreover, it first increased and then decreased with the increase of potassium concentration sprayed. The increase in potassium concentration significantly promoted the contents of sucrose, citric acid and malic acid in pineapple fruits, with increases ranging from 79.5% to 124.6%, 10.1% to 21.2% and 11.9% to 12.2% respectively, but had a relatively small impact on the contents of fructose and glucose.【Conclusion】Taking into account biomass, mineral elements and flavor comprehensively, foliar spraying of 0.6% KH2PO4 during the fruit development period can promote biomass accumulation, optimize the absorption of nitrogen and potassium nutrients, coordinate the content of sugar-acid components, increase the sugar-acid ratio of fruits, and achieve a synergistic improvement in nutrition and flavor quality, providing an important technical reference for the efficient and high-quality cultivation of pineapples.