An investigation into citrus fruit quality problems associated with nutrition in the Murrambidgee Irrigation Areas

Abstract

High juice acidity in Late Valencia oranges (on Poncirus trifoliata rootstock) was found to be a problem in the Murrumbidgee Irrigation Areas (M.I.A.). The problem was investigated by surveying 36 farms in 1971 and 20 farms in 1972. In 1971 about one third of farms produced fruit with citric acid levels above 1.4 per cent; in 1972 fruit from all farms were above this level. High acid levels were associated with excessive use of nitrogen fertilizer. Leaf analyses indicated that nitrogen and potassium levels were above the optimum, phosphorus levels were satisfactory in most cases. Magnesium levels were high-above 0.4 per cent in most instances associated with the high level of exchangeable Mg in the soils, and P. trifoliata rootstock tended to accumulate this element. Juice K and leaf Mg were highly correlated with juice acidity (r = 0.50** and r = 0.38*) and leaf Ca was correlated with the brixlacid ratio (r = 0.46*). Juice nitrogen was correlated with juice acidity.