Growth, yield, and fruit quality in a factorial field experiment with citrus in relation to changes in phosphorus nutrition

Changes in growth, yield, and fruit quality of citrus in a factorial field experiment are presented. Nitrogen fertilization in the sod treatment had only limited effects on yield. After the application of superphosphate, yields at the higher nitrogen levels increased markedly. The initially superior yields from the bare surface treatment decreased gradually, and became at the highest nitrogen level even lower than in the tilled treatments. After application of superphosphate, yields improved in the plots receiving ample nitrogen and became even higher than in the tilled treatments. Yields in the tilled treatments remained good, and were not influenced by nitrogen fertilization. Fruit quality in the no-tillage treatments improved considerably after the application of superphosphate. Increasing nitrogen supply, however, had a depressing effect on fruit quality in all cultural treatment's, but within each nitrogen level the fruit was of similar quality. Nitrogen and phosphorus contents of leaves sampled in 1954 and 1957 are compared, and the changes in yield and quality that occurred during that period are discussed in relation to the modified phosphorus supply in the experiment.