FERTIL I ZER
A fertilizer is any material applied to the soil that supplies nutrients necessary to plant growth. In addition, some fertilizers are applied directly to plants. These products fall into two general categories: synthetic and organic.
Synthetic fertilizers are generally inorganic (meaning they do not contain carbon) and are derived from mineral salts and other synthetic chemicals. The three most important ingredients they provide, called macronutrients, are nitrogen (N), phosphorus (P) and potassium (K).
All synthetic fertilizers are labeled with three numbers, called the fertilizer grade, which indicate the relative percentage of each macronutrient. For example, a bag labeled as “12-12-12” contains 12 percent of each macronutrient, in the form of nitrogen compounds, phosphate (P O ) and potash (K O). Fertilizers are formulated in different balances for specific usages: Nitrogen promotes leaf growth and is recommended for green lawns; phosphorus promotes the growth of roots, flowers, seeds and fruit; potassium promotes the growth of strong stems as well as flowers and fruits. Synthetic fertilizers may also contain secondary nutrients, such as calcium, magnesium and sulfur, as well as other trace minerals.
The chemical compounds in synthetic fertilizers are water soluble, which means they break down easily into their component elements and can be absorbed into the roots of the plant almost immediately. Yet only a fraction of nitrogen-based fertilizer is used by the plant—the downside of synthetic fertilizer is that the chemicals not drawn immediately into the plant are readily washed away in runoff. High concentrations of nitrogen, phosphorus and potassium in runoff collects in waterways with adverse effects. For example, elevated phosphate levels encourage the growth of cyanobacteria in streams and lakes. These organisms can produce harmful toxins that can enter the food chain, eventually affecting the animals and people who consume them. Nitrogen runoff depletes oxygen in the oceans and creates “dead zones” at the mouths of rivers.
Organic fertilizers (which contain carbon) are derived from plant or animal sources, such as peat, manures and composted wastes. These products contain all the same macro-, micro- and trace nutrients as the synthetic fertilizers, but the elements are bound into more complex organic compounds that do not dissolve as readily. This means that it takes longer for the nutrients to be absorbed into the plant roots, but it also means that more of the nutrition remains in the soil with less runoff into the waterways, and the effects of one application last longer. Organic fertilizers