Tomatoes are only as healthy as the soil in which they are planted. To form a bountiful crop of vitamin-packed, colorful, flavorful tomato fruits, several nutritional elements must be present to feed the plants as they grow. Getting soil tested, with store-bought kits or at the local agricultural extension agency, provides a complete rundown of soil composition. Soil amendments, based on test results, create optimal growing conditions for tomato plants.
Tomato plants need phosphorus for development of proteins, photosynthesis, respiration and metabolic transfer processes. Phosphorus is also an integral component of plant membranes. Bone meal and rock phosphate are readily available sources of phosphorus. Since phosphorus does not move well on its own, it is best to work it into the soil before planting or deliver it to the root system through a liquid fertilizer.
Potassium is required for proper sugar and starch formation and protein synthesis. Tomatoes need potassium to breathe properly. When a deficiency exists, the edges of tomato plant foliage start to yellow and die. An excess of potassium can limit the plant's absorption of other key nutrients, such as calcium. Organic sources of potassium include molasses, seaweed and wood ashes.
Tomato plants need nitrogen to synthesize proteins, chlorophyll, coenzymes, amino acids and nucleic acids. Since tomato plants do not produce their own supply of nitrogen, it must be added to the soil before planting and through subsequent feedings throughout the growing season. A soil test is crucial, however, because too much nitrogen can cause excess foliage growth and diminished fruit production. Compost, fish meal and blood meal are organic sources of nitrogen. Inorganic sources include anhydrous ammonia, sodium nitrate and urea.
Tomatoes need calcium for proper development of cell walls and to encourage cell growth and division. Calcium also aids the plant in assimilating nitrogen. Powdered limestone or gypsum, administered to the site before planting, can provide calcium. This form of calcium, however, will affect the soil's pH level. Calcium nitrate, in spray form, is available to use on growing plants. Bone meal and crushed egg shells are organic sources of calcium that can be applied to the soil around the base of the plant.
Magnesium holds several functions within the tomato plant. It helps to control nutrient uptake, carries phosphorus throughout the plant, activates enzymes and contributes to the process of photosynthesis. Yellowing of leaves between veins is a sign of magnesium deficiency. If the deficiency remains, the entire leaf will yellow and wither and growth will be stunted. Foliar sprays of liquid seaweed, or a diluted solution of epsom salts and water are the quickest methods of raising magnesium levels. Dolomitic limestone, applied before planting, is the most practical method of adjusting magnesium levels.