For a plant to thrive, it needs three things: light, water and nutrients. Although plants typically absorb nutrients through soil, they can't always get all of the nutrients that they need through soil. Plants that are unable to obtain the nutrients that they need through the soil often show this neglect through stunted growth, yellowing in color or an inability to produce fruit. To counteract this, farmers, gardeners and houseplant owners often apply fertilizer to the soil to give plants the nutrients that they need.
Nitrogen-rich fertilizers are named so because they contain nitrogen, a macronutrient that all plants need to thrive. Nitrogen is the basis for proteins in plants and animals. Nitrogen-rich fertilizer may be made from decaying matter that is already rich in nitrogen. In compost this may include grass clippings, blood meal, bone meal or peat moss. This is why compost is considered to be a good amendment to garden soil or lawns.
Commercially-made nitrogen-rich fertilizer contains synthesized chemicals such as ammonium or nitrate. Nitrates may be leached from the soil quickly, but plants often absorb it before this can occur. Ammonium is slower to leech from the soil, but they are also slower to be absorbed into plants. For this reason, many nitrogen-rich fertilizers combine both nitrates and ammonium.
Organic fertilizers such as the kind made from grass clippings are more beneficial, but take longer to break down. For this reason, many gardeners start the process of breaking them down by forming a compost pile. By contrast, inorganic fertilizers are quickly absorbed into plants. But many organic gardeners are reluctant to use them because they can be leeched from the soil into the water table and cause pollution.
Although nitrogen is beneficial to plants, it is possible to give a plant too much nitrogen. If a plant is over fertilized with nitrogen, it will appear softer and weaker. Additionally, the excess nitrogen may runoff and pollute nearby water tables. Many gardeners change the ratio of nitrogen in their fertilizers to counteract this by mixing them with phosphorous and potassium in smaller quantities.
Phosphorous is essential in helping plants to form roots, while potassium regulates water absorption in plants. Fertilizers such as this are called N-P-K fertilizers. The N stands for nitrogen, while the p is a notation for phosphorous and the k is a symbol for potassium. When you purchase a fertilizer in the store, it will have numbers in this order to notate the ration of nitrogen, phosphorous and potassium that the fertilizer contains.