The development of cuttings of the Washington navel orange to the stage of fruit set. IV. The effect of different nitrogen and phosphorus levels on fruiting cuttings

Washington Navel orange cuttings, which had flowered 6 months after striking and had set fruit, were subjected to three nitrogen and three phosphorus levels in factorial combination. Increasing nitrogen and phosphorus supply caused a relatively greater increase in the fresh weight of the peel and rag of the fruit than in that of the juice, and this was reflected in a greater diameter of the fruit, a thicker peel, and a decrease in the percentage juice content. The acidity and sugar content of the juice differed little between nitrogen levels, but a marked decrease in both was apparent with increasing phosphorus supply. The results are compared with those of a field experiment. The adverse effects of increasing nitrogen supply on fruit quality were similar in the two experiments. In the glass-house experiment, some improvement in fruit quality with increasing phosphorus levels was only apparent at the low nitrogen level. The dominant role of fruit development with respect to vegetative growth observed in the previous paper of this series was confirmed. Leaves on fruiting shoots showed considerably lower nitrogen and phosphorus contents than the remainder of the leaves, particularly at the higher levels of nutrition.