Nitrogen is a potent nutrient. It is a component of proteins, genetic material (the nucleic acids DNA and RNA), chlorophyll, and many other compounds that are vital in plant metabolism. About 85% or more of the nitrogen in plants is in protein. Application of nitrogen fertilizers will be increase yield potential and recovery growth . however, over-application of nitrogen may have adverse effects on growth and quality. Some of the effects of limited, optimum, and excessive nitrogen fertilization follow.
Applications of nitrogen fertilizers to plants promote vegetative growth (leaves, stems, roots) and reproductive growth (flowers, fruits, seeds). With crops that are grown for their vegetation, such as spinach, lettuce, and celery, the promotion of vegetative growth by nitrogen is a favorable response. However, with root crops, for example, beets and carrots, stimulation of shoot growth may be so strong that yields of roots are diminished by application of nitrogen.
Effects on succulence
Nitrogen fertilization increases the proportion of water in plants and increases the succulence or juiciness of vegetative parts. Succulence is a desirable feature in many vegetables—lettuce, spinach, radish, celery, and others for which the vegetative portion is edible portion. Possibly, the succulence of fruits can be raised by nitrogen fertilization, but the effects will be smaller than those on the vegetation.
Effects on cell walls
Cell walls of plants that are well nourished with nitrogen are thinner than those receiving lesser amounts of nitrogen. Nitrogen in plants promotes protein synthesis at the expense of carbohydrate synthesis and accumulation. Cell walls are made of carbohydrates or of materials derived from carbohydrates. The thin cell walls and high water content give characteristics of succulence and crispness to vegetables. These vegetables are not firous or tough.
Effects on Plant Maturation
The maturation of a crop is slowed by nitrogen fertilization. Nitrogen fertilization be appropriate for the kind of crop that is being grown, that is, whether the crop is grown for its vegetation or fruits or seeds and whether the crop has a short or long season for maturation. Through its effect on growth regulators (hormones), nitrogen fertilization enhances and prolongs the vegetative stage of plant development. Flowering and fruiting may be delayed by nitrogen fertilization.