What exactly is fertilizer? And, why do plants benefit from it?
Fertilizer is simply a material added to soils or directly to plant tissues that contains nutrients essential to the growth and health of the plant. Usually, this means Phosphorous, Nitrogen, and Potassium. These basic elements are usually in the form of chemical compounds that can be converted by the plant to access the needed elements. For instance, plants require Nitrogen, but use it in the form of larger compounds like ammonia (NH4) or nitrate (NO3-). Soils naturally contain these required chemical compounds, but often there is an imbalanced ratio. Fertilizers are inputs that farmers and gardeners can use to increase the amounts and balance the ratios of these essential chemical compounds.
Soil is not dirt. Soil is very much a living, breathing, organic system of nutrients and matter, which plants draw from to build themselves. When you look at a plant, and think of all the matter making up that plant, you realize that all of it came from three places: air, water, and soil. In nature, those plants will die and decompose back into the soil, helping to return much of that matter. In farming and gardening, the plants are removed from their location, to be consumed. This means that all of that matter has now exited the soil permanently. Over years of use, soils become less nutritious. To mend this, we add inputs back into the soil. Often times, this is in the form of a fertilizer.
Replacing and fortifying nutrient levels is key to maintaining healthy soils. See the infographic below for a visual guide to understanding some fertilizer basics!