Nitrogen is viewed to be the most important of all the nutrients in fertilizers. It is also the most difficult nutrient to measure in soil. The microbes in the soil control the day to day supply of nitrogen. In long spells of cold, dry or wet weather, the microbes are slowed down, consequently affecting nitrogen release in the soil. Too much nitrogen is not good since it can cause fertilizer burn. It can even retard the growth of crops or lead to excessive vegetative growth. Different vegetables have different requirements for nitrogen.
Distinguishing Between Fertilizers
One of the easiest ways to figure out nutrient content in fertilizer is to remember that fertilizers are categorized by the amounts of nitrogen, phosphorus and potassium, or the N-P-K ratio. The highest nitrogen fertilizer, ammonium nitrate, contains the ratio of 33-0-0 or 34-0-0, but this is only to be used in special soil and growth conditions. Similarly, the balanced fertilizer, as the name implies, contains a balance of all three nutrients in a ratio of 6-6-6, 8-8-8 or 10-10-10.
High Nitrogen Requirement
Vegetables that require high nitrogen levels include beets, Brussels sprouts, broccoli, cabbage, cauliflower, Asian greens, potato, leek, spinach and Swiss chard. High nitrogen ratio in fertilizers is 16-5-5.
Medium Nitrogen Requirement
Vegetables that have a medium or balanced nitrogen requirement include chicory, asparagus, eggplant, lettuce, garlic, onion, squash, pepper, tomato and sweet corn. A balanced nitrogen ratio in fertilizers is 16-16-16.
Low Nitrogen Requirement
Vegetables that require a low level of nitrogen include cucumber, carrots, fava beans, peas, radish, parsnip, turnip and rutabaga. A low nitrogen ratio in fertilizers is 5-10-10.
Nitrogen for Fruit Bearing Vegetables
The fruit-bearing vegetables such as eggplant, cucumber, pepper, melon and tomato need a good dose of nitrogen in order to start off a healthy plant. But later as the fruit starts to form they need a fertilizer that has high concentrations of potash.
Tips for Fertilizing the Vegetable Garden
For optimal production, fertilizers need to be added every year to the vegetable garden. The best way to determine the levels of phosphorus, nitrogen and potash in the soil is through a soil test. Soil tests determine exactly how much nutrient needs to be added to the soil in view of the vegetables that are being grown. The easiest way to fertilize is to use a good quality commercial fertilizer made specifically for vegetable gardening. Generally, the leafy vegetables and corn need greater quantities of nitrogen, the pod and fruit crops require more phosphorus, and the root vegetables need an extra kick of potash. Unless the soil is markedly deficient in the important nutrients it is often not important to use special fertilizers for the different vegetables in smaller gardens. However, in large commercial vegetable crops, the soil analysis is targeted to match specific crops.