Decreased nitrogen rates and irrigation effect on celery yield and internal quality

The effect of decreased nitrogen rates (90, 60 and 30 kg N/ha) with and without irrigation on celery yield quantity and internal quality were studied in field experiments in 1993 and 1994. The decreased nitrogen rates reduced yields in both years. In the dry and warm conditions of 1994 nitrogen x irrigation interaction was clearly observed; irrigation increased yield more at higher nitrogen rates than at lower nitrogen rates. In the rainy conditions of 1993 irrigation did not effect the yield level. On the other hand, in both years, decreased nitrogen rates increased dry matter, vitamin C and dietary fiber contents, and nitrogen had a minor effect on total sugar content. In 1994 alpha-and beta carotene and thiamin were also analyzed but nitrogen had no effect on them. Irrigation increased dry matter and total sugar contents at the two lowest nitrogen rates in 1994, but decreased vitamin C contents in both years. There was also slight evidence that irrigation might decrease a]pha-and beta-carotene and thiamin contents.