The role of potassium in determining fruit quality of sweet orange

The causes of poor fruit quality, particularly high acid content, of oranges in the Murrumbidgee Irrigation Areas (M.I.A.) were investigated. In a two year sand culture experiment, using Washington Navel orange cuttings, the fruit quality factor most affected by potassium nutrition was juice acidity, with low K levels resulting in low acidity, and thinner peel, In the second season the no potassium treatment also had some adverse effects on fruit quality. Regression analyses on data obtained from a long term citrus experiment showed that high leaf potassium was associated with high acidity in Washington Navel, and with low juice content, high acidity and thick peel in Late Valencia. High leaf P was associated with high juice content, low acidity, thin peel and, for Late Valencia, low sugar content also. Data obtained from Washington Navel fruit taken from nine farms in the M.I.A. were subjected to regression analyses. Rootstocks were rough lemon (eight farms) and sweet orange (one farm). Mineral contents of leaves and juice were correlated, but juice contents were more strongly correlated with quality. High levels of K in the juice were associated with high acidity, while high P levels were correlated with low acidity. High levels of P were associated with high juice content.