Studies in citrus nutrition. 2. Phosphorus deficiency and fruit quality

Abstract

The effects of four cultural treatments and four nitrogen levels on fruit quality, percentage leaf phosphorus, and percentage leaf nitrogen in an experimental citrus orchard are presented. In general, the trees in the tilled treatments, which receive some superphosphate to secure a good growth of the winter cover crop, produce fruit of better quality than those in the notillage treatments. Increasing levels of nitrogen supply in the latter cause a marked decrease in fruit quality. This effect is associated with a decrease in leaf phosphorus in these treatments. Analyses of soils in the different cultural treatments point also to an unfavourable phosphorus status for the no-tillage treatments. A comparison with earlier results in this experiment indicates that fruit quality, particularly in the no-tillage treatments, is deteriorating. This progressive decline is shown to be related to a deterioration in the phosphorus status of the trees in these treatments. Highly significant correlations are reported between fruit quality indices and leaf phosphorus content. Less significant correlations were established with readily available soil phosphorus. These correlations were established in a survey of selected orchards in the Murrumbidgee Irrigation Areas, and similar correlations were obtained for the experimental orchard.