Nitrogen is deficient in almost all soils. Nitrogen is essential in the formation of plant protein, fiber, enzymes, chlorophyll (green leaf pigment), and many other compounds. When a plant becomes deficient in nitrogen, it breaks down chlorophyll and other compounds in its older leaves to recover nitrogen, which it reuses for new growth. This loss of chlorophyll causes the older leaves to turn yellow. Soils that are low in organic matter, and sandy, readily leached soils are frequently deficient in nitrogen. These kinds of soils, in particular, need to be supplemented with fertilizers. Poor drainage, cold (50°F and below), and acidity or alkalinity can also cause soil nitrogen to become less available for plant use.
Spray the foliage with a fertilizer containing nitrogen for a quick response. Fertilize plants with a fertilizer containing nitrogen. (For more information about fertilizers, see Nitrogen, How Much Water to Apply.)
Plant Care for Citrus