English abstract
A field study was conducted with five citrus cultivars grown in clay soil in Kewesna, Monufia, Egypt for two successive growing seasons. The study aimed at using nutrient concentrations in the leaves as a guide for proper fertilization. The study revealed that most of the nutrients in the soil were at adequate levels. However, there were unfavourable soil conditions that affected negatively nutrient availability. Nutrient concentrations in the leaves of the five cultivars were nearly the same, except for a few cases. Leaf nitrogen concentrations were at adequate levels. To minimize the usage of fertilizers, the quantity of N-fertilizer should not exceed 100 kg N per feddan, added as three doses in September, March and June. Phosphorus fertilızers should be added in September and when another dose is needed, it should be in May. For such a clay soil, nearly double the potassium requirement of the crop should be added as split application. More attention should be given to magnesium fertilization Micronutrients concentrations were at adequate levels. However, under such soil conditions, fertilizers of acidic reactions are recommended and micronutrients should be supplied as foliar sprays in September, March and May. Adequate levels of the nutrients in the 5-7 months spring flush together with the high obtained yields suggest that the obtained levels of the nutrients (except copper) can be used as a basis to correct the fertilizer programmes at any growth stage.
