Nitrogen, Phosphate & Potash for Plants

Nitrogen

• Plants need nitrogen to grow and to perform photosynthesis. Nitrogen is a vital part of the proteins that build cells and tissue. Nitrogen is also a major ingredient in chlorophyll, the pigment that gives plants their green color and the part of the plant responsible for photosynthesis. The air we breathe is 78 percent nitrogen, but only legumes such as beans and alfalfa can fix nitrogen from the atmosphere into the soil. All other plants absorb it from the soil through their roots. Stunted growth from a lack of protein and yellowing leaves from a lack of chlorophyll are signs of nitrogen deficiency.

Phosphorus

• Phosphorus plays an essential part in photosynthesis, seed formation and healthy root growth. The foliage on plants deficient in phosphorus turns dark green, brown, red or purple. Plants appear stunted with thin stems and few flowers or fruit forming. When phosphorus is insufficient, potato plants curl their leaves upward and the potato tubers form with brown specks on the inside. High-acid or high-alkaline soils lack phosphorus. Adjust the pH level of the soil before amending with a phosphorus-rich fertilizer like bone meal.

Potassium

• Although potassium does not play a major role in the formation of any plant structure, it is essential to the functioning of various plant systems such as photosynthesis, water transportation through the plant and disease resistance. Potassium is applied to the soil as potash, a water soluble form of potassium. Potassium-deficient plants appear stunted with yellowed or browned leaf edges. Stems and stalks become weak and the plant is unable to resist diseases. Annual plants lacking in potassium lose their winter hardiness and may not return in spring.

Application

• The three numbers on the labels of commercial fertilizers indicate the amount of these important nutrients in the fertilizers. The first number is the percentage of nitrogen, the second is the percentage of phosphorus, and the third is the percentage of potassium. Take soil samples for testing to your local cooperative extension office and check the nutrient requirements of the plants in your garden before applying fertilizers. Do not over-fertilize. Too much fertilizer can be as harmful as not enough and excess fertilizer washes away during rain storms or irrigation and contaminates water bodies. Read the labels and follow the manufacturer's recommendations.