Vegetables plants need essential elements to grow and develop healthy leaves, stems and crop. Although most of these nutrients are naturally present in the soil, adding organic or commercial fertilizers amend it further and enrich the quality. A soil test determines the existing nutrients in the soil, allowing you to use a fertilizer packed with those elements.
An essential component in chlorophyll, nitrogen encourages the plants to make their own food and maintain the green color. Plants start turning yellow if they fail to receive ample nitrogen. Urea, ammonium nitrate and calcium nitrate are examples of a few commercial nitrogen-containing fertilizers. Some garden soils are enriched with most nutrients except nitrogen, which is why they require a fertilizer that is packed with it. According to the Mississippi State University Extension, amend such soils with 3 lbs. of nitrogen-rich fertilizer for every 1000 square feet of area.
Vegetables such as peas and beans add nitrogen to the soil. Green leafy plants, broccoli and corn require moderate amounts of nitrogen in the soil. It is best to enrich the soil prior to planting by adding and mixing nitrogen fertilizer. Also apply nitrogen-rich fertilizer to these vegetables after they become established. However, make sure not to over fertilize the plants as excessive nitrogen causes foliage to turn yellow and immature crop to split. Nitrogen in organic form is present in well-rotted animal manure. For best results till fresh manure into the soil prior to planting seeds, and spread composted manure around existing plants.
Most vegetable plants benefit from an occasional doze of well-balanced fertilizers (N-P-K), or those with equal amounts of nitrogen, potassium and phosphorus. Nitrogen is essential for building food, phosphorus or phosphate is an essential cell-building block, and potassium or potash ensures healthy and strong stalks. Tomatoes and other root plants and vegetables require a well-balanced 10-10-10 fertilizer for a healthy produce. According to the United States Department of Agriculture, you should test your garden soil every three years, preferably in the fall, and adjust fertilizer mix accordingly.
Organic fertilizers are packed with natural elements that are environmentally friendly and lack chemical additives. Fish emulsion, compost, peat moss, animal manure and perlite are examples of some organic fertilizers. The Florida Cooperative Extension Service suggests working organic fertilizers into the soil at least three weeks before planting vegetables. For every 100 square feet of area, apply 25 lbs. of animal manure and 3 lbs. of rock phosphate or bone meal to provide essential nutrients and improve existing drainage. Apply 5 lbs. of manure to the vegetable plants when they are established.