From apples to zoysia grass, all plants need 13 elements from the soil to grow and produce. Most soils do not contain sufficient levels of the most critical elements to sustain long-term growth of turf grass, fruits, vegetables, grains and forages. Gardeners and farmers can increase the level of these elements in the soil by applying fertilizer.
Nitrogen, phosphorus and potassium are the elements plants consume in the greatest abundance. These are the macronutrients. Calcium, sulfur and magnesium make up the next group, referred to as the secondary nutrients. Boron, iron, manganese, copper, zinc, molybdenum and chlorine are used in very small quantities and are referred to as the micronutrients. Every fertilizer on the market must list its percentage of nitrogen, phosphorus and potassium on the label. For example, fertilizer marked 16-2-2 is 16 percent nitrogen by weight, with 2 percent by weight of phosphorus and potassium.
Traditional synthetic fertilizers refine naturally occurring products to produce water-soluble forms of nitrogen, phosphorus and potassium. They offer few, if any, secondary or micronutrients. Some have been further processed to slow down the dissolution of the elements. These "slow-release" products provide nutrients for the plants over a longer period of time, with less chance of giving the plant too much at once. Synthetic fertilizers are immediately available to the plant, yielding quick results after application.
Organic fertilizers combine naturally occurring sources into products that contain all the plant nutrients, not just the macronutrients. Lower concentrations of the nutrients make it necessary to use considerably more product to achieve the same application rate. Organic fertilizers are slow release by nature. Biological processes that take place in the soil make the nutrients available to plants. These processes take time, meaning that organic fertilizer will not provide the immediately apparent effect that synthetic fertilizers will. Organics are derived from a wide variety of base products, from grain milling byproducts and poultry manure to processed sewage sludge.
Over-applied synthetic nitrogen and phosphorus leach into the water that runs off fertilized areas causing problems in our streams, rivers and lakes. Organics are not a perfect solution for the problem. They cause similar problems, but it takes a much larger application and much longer for the leaching to take place. Gardeners, homeowners and the agricultural industry all have to take responsibility for careful use of fertilizers and apply only what the plants can use.
Continued use of synthetic fertilizers can have a negative impact on soil structure. A balanced approach, combining compost, cover crops, organic fertilizers and carefully timed, carefully measured synthetic applications can deliver the bounty the gardener is looking for, while enriching the soil for future years and protecting the environment.